Download Radio Shack 112 Instruction manual
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T h i s P R O J E C TB O A R D A S C I I K E Y B O A R DE N C O D E Ru t r l i z e sT T L l o g i c T h e A S C I I K E Y B O A R DE N C O D E R m a y b e u s e d t o p r o v i d ei n p u t st o a l l t y p e so f e q u r p m e n d t e s i g n e dt o o p e r a t ew i t h A S C I I ( A m e r i c a nS t a n d a r d Code for Information Interchange)rnputs Examples of such equipment are. T V typewriters, m i n i - c o m p u t e r s , m r c r o - p r o c e s s oorrsa n y d e v r c ew h r c h r e q u i r e sA S C I Ie n c o d e ra l p h a - n u m e r i cc h a r a c t e r s F e a t u r e so f t h e A S C I I K E Y B O A R DE N C O D E Ri n c l u d e . R e p e a tk e y c o n t r o l sa l l c h a r a c t e r sa n d s y m b o l s N e g a t i v e - g o r n go r p o s i t i v e - g o i n gd a t a v a l i d s t r o b e Latch outputs (storeslast key code) Shift and shift lockcapabrlrty T r u e o r f a l s e A S C I Io u t o u t s Six extra control kevs la :{ P h o t o g r a p hi s t h e c o m p l e t e dp r o l e c tw h e n b u r l tw r t h t h e r e c o m m e n d e dR a d i oS h a c k p a r t s T h i s p a c k a g e c o n t a i n so n l y t h e P r i n t e dC i r c u i t B o a r d ,a n I n t e g r a t e dC i r c u i t a n d i n s t r u c t t o n s iii rt: ASCII ENCGIDEFI TABLE OF CONTENTS 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. fntroduction S p e c i f i c a t i o n. .s. Description Partslist AssemblyofthePrintedCircuitBoard P a r t s M o u n t i n .g. Testing T r o u b l e s h o o t i n. g T h e o r y oOf p e r a t i o n WaveForms S c h e m a t iDc i a g r a m ....2 . .... 3 . .... 4 .......5 ......6 .....6 ... .. ... 11 ....19 ........22 ...26 . .. .. . .. 27 ASCII KEYBOARD ENCODER PROJECTBOARD INTRODUCTION T h i s p a c k a g ec o n t a i n s a P r o j e c tB o a r d( P r i n t e dC i r c u i t B o a r d ) ,a n I n t e g r a t e d C i r c u i t a n d l n s t r u c t i o n M a n u a l for constructing an ASCII KeyboardEncoder. The Instruction Manual provides a complete list of parts needed to complete your project. lt also provides theory of operation,assembly instructions and diagrams to aid you in your project. T h e A S C I I K e y b o a r d E n c o d e rc a n b e u s e d t o p r o v i d e i n p u t s t o a l l t y p e s o f e q u i p m e n t d e s i g n e dt o o p e r a t e w i t h A S C I I ( A m e r i c a n S t a n d a r dC o d ef o r I n f o r m a t i o n lnterchange) inputs. Examples include T.V. typewriters, mini-computers, micro-processors, electric typewriters or anv device which requires A S C I I e n c o d e da l p h a - n u m e r i c a lc h a r a c t e r s T h r o u g h o u tt h i s m a n u a l y o u w i l l s e e s y m b o l ss u c h a s 8 , E o r H E X T h e l i n e a b o v et h e c h a r a c t e r sr e p r e s e n t s N O T ( n e g a t i v e )l o g i c w h i c h i s t h e s t a t e o p p o s i t e o f that without the bar HEX means "hexadecimal" which is a number systemthat has a base of 16. Note that this Project Board requires an external p o w e r s o u r c e - 5 v o l t s D C a t a b o u t 5 O Om A S u c h a power supply could be another Radio Shack Project B o a r d , C a t a l o gN u m b e r 2 7 7 - 1 O 2 o r 2 7 7 - 1 1 2 O r i t may be powered by the equipment to which you connect the ASCII Keyboard Encoder. RAD|OSHACK ^ DtVtStONOF TANDYCORPORAflON E U.S.A.:FORTWORTH,TEXAS76102 C A N A D A :B A R R I EO , N T A R I OC. A N A D AL 4 M 4 W 5 T A NDY CORPORATION AUSTRALIA 2 8 03 r 6V T C T 0 R RToA A0 RYDALME NR SE W 2I16 ' 8 7 6 S p - 2 8 4 7- 9 9 0 - 0 I 8 4 ',) BE L GUI M PARCINDUSTRIELt]E NANINNE 5 1 4 0N A N I N N E UK E I L S T ORNO A I ] W S I O7 J N W E O N E S E USRTYA f F S P R I N T E DI N U S A . --.*,-i:*:- - ASCII ENGC'E'EF SPECIFICATIONS l-- lnput Voltage: MrN. 4.7 E 5.O MAX. 5.5 UN|T VoltsDC Input Current: 4OO 450 50O mA Charactersper Minute Output: *Note 1 833 CPM nepeat Key Rate: **Note 2 2oB cPM 10 10 I 10 10 10 TTL Loads TTL Loads TTL Loads TTL Loads TTL Loads TTL Loads t ,l - Output Drives: ASCIlTrueOutput: Ascll ffid Output: ST Output: ST Output: E Output: E Output: Outputs: 7-bitTrueASCII z-uitffi6 Ascrl 1-bit E (6;5-le) External defined controt bit 1-bit E (Enable)Externaldefinedcontrol bit 1-ST Fallingedge clock 1-Si nising edge clock ; I Inputs: +5.OVOLTS DC ! 2% load and line regulation, 50 mV peak-to-peak ripple Ground *Note 1 : Specifiedwith l kHzclock frequencyand with 2 scan cyclesper keypressedand 2 scan cyclesper key released.A scancycleis equalto 18 clockcycles.Thereforeminimum keytime = 18 x 4 x J- = 72 1kHz ms = 13.8 characters per second. **Note 2: Specifiedwith 1 kHz clockfrequency.Repeatrate is 16 scancycleslongwhich is equalto 288 clock cycles= 0.288 seconds= 3.472 charactersper second. I I 3 ASiCII DESCRIPTION 5. Shift Logic R e f e rt o F i g u r e1 , B l o c kD i a g r a m . 6. Output Latches The ASCIIKeyboardEncoderusesthe scanprinciple to reduce the amount of logic necessaryto fully encodea 63 keytypewriterkeyboard.TheKeyboardis w i r e d i n t o a m a t r i xc o n s i s t i n g o f 1 6 c o l u m n sa n d 7 rows of keys.Sincethis typeof matrixcan handlea Keyboard with 112 switches. there are many locations that have no key. The keyboardscan principle, which has been used on all recent calculators,has the advantageof minimizedeffects of key bounce.(Keybounceis that tendencyof a key to chatter,or double-entry, when pressedor when released. ) 7. Repeat Logic The Keyboard Encoder is divided into 7 major subsections: 1. Keyboard 2. KeyboardScanner ENCC'E'EFI The Keyboard together with the Scanner logic supplies the Key PressedDetectorand the Encoder L o g i c w i t h p u l s e s . T h e K e y P r e s s e dL o g i c w a i t s u n t i l the key is released and then providesa strobe that c l o c k s t h e e n c o d e d d a t a o u t o f t h e K e y b o a r dE n c o d e r . The Encoder section generates the three most significant ASCII bits and passes them on to the O u t p u t L a t c h e s .l f a s h i f t i s r e q u e s t e d ,t h e S h i f t L o g i c further modifies the encoded three bits to give a s h i f t e d c h a r a c t e r .T h e f o u r l e a s t s i g n i fi c a n t b i t s o f t h e ASCII encoded word are generated by the four-bit binary counter controlling the scanner. The 7-bit ASCII code is held in the data latchesuntil a new key i s p r e s s e d ,a t w h i c h t i m e t h e p r o c e s ss t a r t s o v e r . T h e r e p e a t l o g i c r e s p o n d st o t h e r e p e a t k e y w h i c h c a u s e s the strobe command to turn off and on at a p p r o x i m a t e l y 4 H z . . . w h i c h r e p e a t e d l yc l o c k s o u t the data held in the latches. 3. Key PressedDetector F o r a d e t a i l e d d e s c r i p t i o no f t h e T h e o r y o f O p e r a t i o n , refer to the back of this manual. 4. Encoder KEYPRESSED OETECTOR F I G U R E1 . 4 B L O C KD I A G R A M ASC|! ENCC'E,EFI PARTSLIST T h i s p a c k a g e c o n t a i n s a c o m p l e t e c i r c u i t c a r d ( P r o j e c tB o a r d 2 7 7 - 1 1 7 1 r e a d y f o r p a r t s t o b e a d d e d . l t a l s o c o n t a i n s I n t e g r a t e dC i r c u i t , R S 7 4 H 1 0 3 ( 2 1 ) T o c o n s t r u c t y o u r A S C I I K e y b o a r dE n c o d e r ,y o u w i l l n e e d t h e f o l l o w i n g p a r t s . A l l p a r t s a r e a v a i l a b l ef r o m y o u r R a d i o S h a c k S t o r e . NOTE: T h e v o l t a g e r a t i n g s h o w n f o r c a p a c i t o r si s t h e m i n i m u m w o r k i n g v o l t a g e C a p a c i t o r so f t h e s a m e c a p a c i t a n c ev a l u e w i t h a g r e a t e rw o r k i n g v o l t a g em a y b e u s e d A l s o n o t e t h a t r e s i s t o r sa r e l i s t e da s 1 / 4 - w a t t . 5 % " .b u t . r e s i s t o r s r a t e d a t 1 / 2 - w a t t , 1 O % w i l l w o r k SYMBOL DESCRIPTION RADIOSHACK CAT.NO. SYMBOL E+\ -l A- .l I 10\ 1\ - 272-131 272-14OO 272-14OO 272-131 272-131 272-131 14\ 15\ RESISTORS i*r \ ./ ./ '// . / 1 # R\ R n 8 8 'R10\ 8K,1/4-wa*,svo 330 ohm, i /4-warr, so/o lK, 1/ -watt,sYo l K , 1 / 4 - w a t t ,5 % 1K, 1/4-watt, 5o/o l K , 1 / 4 - w a t t ,5 % 1 K ,1 / 4 - w a n , 5 % 1K, 1/4-wart, 5o/o 1 K , 1 / - w a t r ,5 % lK, 1/ 4-wan, 5o/o 1K,1/4-watr,sYo 27 1 -1300 271-1300 271-1300 27 1 -1300 27 1 -1300 271-1300 27 1 -1300 27 1 -1300 27 1 -1300 271-13OO.,. 271-1300 RADIOSHACK CAT. NO. 276-1809 R S 7 4 2 OD, u a l ,4 - i n p u t N A N DG a t e 276-1802 R S 7 4 O 4H, E X I n v e r t e r 276-1820 R S 7 4 1 9 3S , ynchronous 4-bit up/down counter 276-1834 RS741 54, 16-line Demultiolexer R57473,Dual,J-K Flip-Flop276-1803 RS74O4,HEX Inverter 276-1802 RS74O2,Ouad,2-input 276-1811 N O RG a t e 276-1801 CAPACITORS O 01 ptF,SOV,disc 3 . 3 1 t F1, O V T , antalum T 3.3uF, 1OV, antal-um o oi prF5OV,disc 0 . 0 1p F 5OV,disc o.otpr SOV,disc DESCRIPTION 17 \ R S 7 4 1 OT, r i p l e ,3 - i n p u t NAND Gate 276-1807 276-1809 KEYBOARD \f\ 63 Key Board 275-1422 O p t i o n afor l HeepTest Module I N T E G R A T ECDI R C U I T S z+\ D z3\ z lZ5r v r\ lA. l8- CONNECTOR Included R S 7 4 H 1 0 3D, u a l ,E d g e T r i g g e r e Jd - K F l i p - F l o p ( R e c e i v ew dith package) R S 7 4 7 3 ,D u a l ,J - K F l i p - F l o p276-1803 276-1820 R S 7 4 19 3 . S v n c h r o n o u s 4-bit uo/down counter RS747 5,14-bitBisrableLatclr2 7 6 -18 0 6 RS7475, 4-bit BistableLatch276-1806 R S 7 4 1 3D , u a l ,4 - i n p u t 2t6-1815 S c h m i t tT r r g g e r R 5 7 4 0 0 ,O u a d ,2 - i n p u t 276-1801 N A N DG a t e R S 7 4 1 0T, n p l e 3 276-1801 , -input N A N DG a t e ,/-\ ,/ EdgeCard,44 contact )(one needed) 276-1551 RESTSTOR / J -/ 180 ohm, i /4-warr, so/o (nine needeo; 276-1300 L I G H TE M I T T I N G DIODE /-, LED (nine needed) 2-/6-O90 ASCII ENCC'ElEFI A S S E M B L Y O F T H E P R I N T E DC I R C U I T B O A R D Assembling of the Printed Board consists of m o u n t i n g c o m p o n e n t s t o t h e B o a r d .T h e P A R T SL I S T notes the parts you'll need The Board contains l e t t e r i n g i d e n t i f y i n g w h e r e t h e c o m p o n e n t sa r e t o b e m o u n t e d . A l s o i f a p p r o p r i a t e ,y o u ' l l s e e t h a t s o m e outlines indicate the position or direction that a component is to be mounted on the Board We recommend that you mount the components in g r o u p s - s u c h a s t h e r e s i s t o r s t, h e n t h e c a p a c i t o r s and then the integrated circuits A step-by-step assembly procedure is provided for each group of components. As you mount each component check off that step Efin the box. Some Notes Before You Start D u e t o t h e s m a l l f o i l a r e a a r o u n c it h e P r i n t e dC i r c u i t Board holes and the small areasbetweenthe foils, you will have to use utmost care to prevent solder bridges between adjacent foil areas. Use only a l o w - w a t t a g e s o l d e r i n gi r o n w i t h a s m a l l t i p . D O N O T USE A SOLDER GUN. An ideal Solderinglron is R a d i o S h a c k ' s R e c h a r g e a b l el r o n 1 6 4 - 2 0 7 5 1i;t h a s a s m a l l t i p a n d w i l l n o t d a m a g e s e m i c o n d u c t o r sw i t h leakage currents (a problem with some delicate d e v i c e s ) .U s e o n l y a m i n i m u m a m o u n t o f s o l d e r ,a n d d o n o t h e a t c o m p o n e n t s e x c e s s i v e l yw i t h s o l d e r i n g i r o n .T r a n s i s t o r sa n d p r i n t e dc i r c u i t sc a n b e d a m a g e d i f s u b j e c t e d t o e x c e s s i v ea m o u n t s o f h e a t T h e P r i n t e d C i r c u i t B o a r d i s a d o u b l e - s i d e do n e , w i t h p l a t e d - t h r o u g hh o l e s .T h i s m e a n s t h a t i n a n u m b e r o f locations,the foil paths on the top of the Board are connectedto the foil paths on the bottom - through holes which have plating on the inside. This p l a t e d - t h r o u g ht e c h n i q u e m e a n s y o u d o n ' t h a v e t o s o l d e rc o m m o n f o i l a r e a so n B O T Hs i d e s- s o l d e r i n g o n t h e b o t t o m s i d e o n l y n o r m a l l yw i l l b e a d e q u a t e U s e a n o h m m e t e r t o c h e c kt h e p l a t e d - t h r o u g hh o l e s f o r c o n t i n u i t y p r i o r t o a s s e m b l i n gt h e K e y b o a r d . One last pointer - if you keep the tip of your iron clean and coated with a f resh laverof melted solder, y o u ' l l f i n d s o l d e r c o n n e c t i o n sm u c h e a s i e rt o m a k e P e r i o d i c a l l yw i p e o f f t h e t i p o f y o u r i r o n o n a d a m p r a g ( o r " s o l d e r s p o n g e " )a n d m e l t a f r e s h l a y e r o f s o l d e r over rt. P a r t sM o u n t i n g M o u n t t h e f o l l o w i n gr e s i s t o r s : ! R 1 , 6 8 K ( b l u e ,g r a y ,r e d ) ! R2, 330 ohm (orange,orange,brown) n R 3 , 1 K ( b r o w n ,b l a c kr e d ) , l a c k ,r e d ) n R4, 1K (brownb tr R5, 1K (brown,black,red) ! R 6 , 1 K ( b r o w n ,b l a c k ,r e d ) t r R 7 , 1 K ( b r o w n ,b l a c k ,r e d ) ! R8, 1K (brown.black,red) ! R 9 , 1 K ( b r o w n ,b l a c k ,r e d ) n R 1 O ,1 K ( b r o w n ,b l a c k ,r e d ) ! R 11 , 1 K ( b r o w n b, l a c k r, e d ) !Turn the board over and solder.Trim off excess l e a dl e n g t h M o u n t t h e f o l l o w i n gc a p a c i i o r s : NOTE: C a p a c i t o r sC 2 a n d C 3 a r e p o l a r i t y c o n s c i o u sW h e n i n s t a l l i n gc a p a c i t o rC s2 and C3, observepolarity.With the dot on t h e c a p a c i t ofra c i n gy o u ,t h e l e a do n y o u r r i g h t i s p o s i t i v e( + ) f l C 1 , O 0 1 1 t F ,S O V ,D i s c ! C 2 , 3 3 g F , 1 O V ,T a n t a l u m (Observe polarity) (Observp eolarity) ! C 3 , 3 3 1 t F , l O V ,T a n t a l u m ! C4, O 01 1tF,5OV,Disc n C5, O.O1prF, SOV,Disc ! C6, 0.01 prF,SOV,Disc !Turn the board over and solder Trim off excess l e a dl e n g t h . -4 ru 0 NK]LHTE D o -Q m { FIGURE2. RESISTORAND CAPACITORMOUNTING z o 0 o [l ! ASCil Mount the followingIntegratedCircuits: 424,R57475, 4-bit BistableLatch NOTE: DZs, R57475, 4-bit BistableLatch Y o um a y w a n t t o u s e s o c k e t s f o r t h e l C ' s if so now is the time to mount them. ENCC'E'EFI f l 2 6 , R S 7 4 1 3 ,D u a l ,4 - i n p u t S c h m i t tT r i g g e r 1. Install the IntegratedCircuits (lC) in their correctpositions. 2. The pins protrudethrough the holes in the PrintedCircuitBoard. 3. NOTE: A dot or indentation at one end i n d i c a t e sp i n 1 . 4. Ensure that the Integrated Circuits are positionedproperly. 5. As you mount each lC, spreadthe end pins slightlyto hold it in placeso you can turn the Board over and solder the pins. aZ7, RS74OO, Ouad,2-input NAND Gate llz8, RS741O,Triple,3-input NAND Gate fl29, RS742O,Dual,4-inputNAND Gate aZ1O, RS74O4.Hex Inverter E Turn the boardover and cleanthe tip of your iron beforesoldering.A cleantip, freshlycoatedwith meltedsolderwill insurea goodconnection.Now carefullysoldereach pin to its adjacentfoil area. 4211, RS74193, Synchronous 4-bit UplDown Counter Dot or a z l 2 , R S 7 4 15 4 , 16 - l i n eD e m u l t i p l e x e r 4213, RS7473,Dual,J-K Flip-Flop ZZ14, RS74O4.Hex Inverter 4215, RS74O2,Ouad, 2-input NOR Gate aZ16, RS74OO, Ouad,2-input NAND Gate nT , RS74H103, DualEdge-triggered J-K Flip-Flop a Z 1 7 , R S 7 4 1 OT, r i p l e ,3 - i n p u tN A N DG a t e NOTE: aZ/ Checkthe positionof this lC carefully.lt is already inserted in the Printed Circuit Boardbut checkfor correctpositionbefore solderingit in place. R57473,Dual,J-K Flip-Flop a23, RS74193, Synchronous 4-bit UplDown Counter 4218, RS742O,Dual,4-input NAND Gate ETurn the boardover and solder. @ D o o lrl z o o m 0 (o F I G U R E3 . I C M O U N T I N G ! AETCII ENCC'EIEFI You are now ready to install the Keyboard to the P r i n t e dC i r c u i t B o a r d .M o u n t a s f o l l o w s : ! Ensure that all of the pins on the Keyboardare STRAIGHT! nThe Keyboardcontainsthree plastic alignment pins on its basewhich mate into alignmentholes in the PrintedCircuitBoard Placethe Kevboard with keys facing a f lat Position the the down on surface. Printed Circuit Board (componentside down) approximatelythree inches above Keyboard. V i s u a l l ya l i g n B o a r da l i g n m e n h t o l e sw i t h p l a s t i c alignmentpins on Keyboardbase.Gently lower the Board onto the Keyboardmaking sure the alignment holes in the Board mate with the alignmentpins on the Keyboardbase.Checkthat ALL Keyboardpins protrudethroughthe holeson the PrintedCircuitBoard. 10 ! Solder one pin at each corner - press the Board f i r m l y d o w n a g a i n s t t h e K e y b o a r da s y o u d o t h i s . T h i s w a y y o u ' l l b e s u r e e a c h p i n e x t e n d sw e l l i n t o the appropriate hole and that the Board and K e y b o a r dm a t e f l a t C o n t i n u e t o s o l d e r a l l p i n s . This completes the component assembly of the Printed Circuit Board. We suggest you check over y o u r w o r k t o e n s u r e t h a t a l l s o l d e rj o i n t s a r e c l e a n a n d s h i n y a n d t h a t n o n e o f t h e f o i l h a s p u l l e du p f r o m the Board due to excessive heat Double check to ensure all component connections are solderedto the foil and that no solder has flowed across (between)foil paths. T o e n s u r e o p t i m u m c i r c u i t p e r f o r m a n c ea n d t o m a k e your work neat,you may want to "deflux" the Board T o r e m o v e a n y r o s i n r e s i d u e ,a p p l y o r d i n a r y r u b b i n g alcohol to the Board and rub off with a clean cloth ASC|| ENCC|E'EFI TESTING LED Cathode ldentification T o t e s t t h e A S C I I K e y b o a r dE n c o d e ry o u ' l l n e e d s o m e f o r m o f d i s p l a y t h a t v e r i fi e s t h e c o d e s .l f y o u h a v e t h i s e q u i p m e n t a v a i l a b l e ,u s e i t t o t e s t y o u r E n c o d e r .S e e Connector Pin ldentification on page 12 for pin c o n fi g u r a t i o n . Due to the reluctance of manufacturers to standardizethe methodof cathodeand anodelead identification,we urge you to test each LED before installing. This can be done in the following manner: With two 1-1/2 volt batteriesconnected in seriesforming a 3-volt power supply,connecta resistor- any valuefrom 1OOohmsto 47Oohmsto the positiveside of the batteries. lf you do not havea systemthat acceptsASCIIcodes for testingwe suggestyou buildyour own. Fabricate the Heep Test Module using Figure 4 and the fabricationprocedures.We show the LED's and resistorsas they should mount on the connector: however,you can mount these componentson an external breadboardaccordingto the schematic shown with the illustration(Figure4). Test the LED'sby connectingone lead of the LEDto the negativesideof the batteriesand the other leadto the resistorwhich is connectedto the positiveside. lf the LED lights,the lead connectedto the negative side is the cathode. lf it does not light, reversethe LED leadsto identifythe cathode. 100oHM TO 470oHM LED TESTDIAGRAM 11 @ ASCII Fabrication Procedures fJ X n n ! Carefullybend the connector'sletteredpins (up)as shown in Figure4. Mount the LED'sbetweenthe followingpairs of pins: (All cathodes of the LED's are connectedto oDD numberedpins.)2-3,4-5, 6 - 7 , 8 - 9 , 1 0 - 1 1 , 1 2 - 1 3 , 1 4 - 1 5 ,1 6 - 1 7 a n d 18 - 19 . M o u n t t h e n i n e , 1 8 0 o h m r e s i s t o r sb y solderingthem to pins as shown. Bend the free lead of the resistorsolderedto pin 18 toward the resistorconnectedto pin 16 and solder. Then continue with the resistor s o l d e r e dt o 1 6 t o 1 4 , 1 4 t o 1 2 ,a n d s o o n a s illustrated.Solder the free lead of the final r e s i s t o tr o p i n 1 . Use any insulatedsmallwire (22to 30 gauge) for followingjumper wires. After measuring distancerequired,cut wires to correctlength, removesmall amountof insulationfrom each end and solderwires as follows: Connect a well-regulated source of S-volts DC b e t w e e n P i n 1 ( + )a n d P i n Z ( - ) .T h e s u p p l ys h o u l d b e c a p a b l e o f s u p p l y i n g a b o u . t5 O Om A . T h e H e e p T e s t M o d u l e c h e c k s t h e K e y b o a r dE n c o d e r o u t p u t s u s i n g L E D ' s ( L i g h t E m i t t i n g D i o d e ' s ) .U s i n g t h e o u t p u t p i n s s p e c i fi ed i n t h e O u t p u t C o d i n g T a b l e , ( p a g e 15 ) a l o g i c a l 1 ( o r t r u e ) i s i n d i c a t e d b y t h e appropriateLED lighting. A logical O (or false) is indicated by the appropriate LED nor lighting P e r f o r m y o u r t e s t s u s i n g t h e t e s t p r o c e d u r e sa l o n g with the Output Coding Table. The output codes s h o u l d m a t c h u p w i t h t h e L E Dd i s p l a y l f y o u d o n ' t g e t correct indicationsrefer to Troubleshooting. Connector Pin ldentification Thefollowingchartcorrelates the ASClloutputcodes to pins on the PrintedCircuitBoard Youcan usethis informationfor connectingthe ASCIIEncoderOutput to externalequipment. ASCII PC BOARD OUTPUT PIN CODE NUMBER 12 From Pin To Pin From Pin To Pin 3 5 7 9 11 21 L P R U 13 15 17 19 B E F K ENCC'DEFT 20 21 22 23 24 25 26 E ST J H D C T S N M X ASCII P CB O A R D OUTPUT PIN CODE NUMBER 20 21 7 T 7 25 T" E ST K F E B U R P L 21 ASCII BLUE J U M P E R S( 4 } ENCG'EIEFI +5.0 VDC l80a 180cl 1 8 0s , 1 8 0s l I t 8 00 I 1 8 0s , 1 8 0s , 1 8 00 IED L^.,^ S C H E X I A I I CD I A G R A A I RED J U M P E R S( 5 ) NOTE: F I G U R E4 . Be sure to coat the tip of your soldering iron with a layer of melted solder before soldering the component leads and wires to the connector terminals. H E E PT E S T M O D U L E 13 @ ASCII TESTPROCEDURE 1. Installthe Heep Test Module on the Printed CircuitBoard. 2. Connect +S-volt DC power to pin 1 of test moduleconnector. 3. Connect ground return to pin Z of test module. 4. Perform test using Output Code Table and observe test module LED indications.The followingis a descriptionand explanationon how to use the tableand how to interpretthe test moduleindications. Lookingat the OutputCodingTable,youseethereare two separategroupsof output codingidentifiedas NORMALand SHIFT.Theseare two separatetests. First,you check the output codesof the Encoderin the NORMAL mode (not in SHIFT LOCK).After completingthe NORMALmode checks,depressthe SHIFTLOCKkey and checkthe outputcodesof the Encoderin the SHIFTmode. F. the next monitors and represents23 output codes, G. the next monitors and represents22, H. the next monitors and represents21, L the next monitors and represents20 F o r a n e x a m p l e , l e t ' s p r e s s t h e f i r s t k e y ( E S C ) .N o t e t h a t a c c o r d i n gt o O u t p u t C o d i n gT a b l et h a t E o u t p u t i s O , 2 6 i s 1 , 2 5 i s 1 , 2 a i s 1 , 2 3i S 1 , 2 2 i s1 , 2 ' i s 1 a n d 2 0i s 0 . W h e n y o u p r e s s t h e k e y E S C ,t h e f i r s t L E D o n t h e H e e p T e s t M o d u l e s h o u l d l i g h t . R e l e a s et h e k e y a n d the first light should go off. 5. 6. A. Thef irst LEDlightswhen a keyis pressedand stayson until you releasethe key at which time the LEDgoes off (not lighted). B. The next LED monitors and representsE output codesand lightswhen E outputcode . is 1 and doesnot lightwhen E outputcodeis 7. o. 14 i I N o w c h e c k t o s e e i f t h e o u t p u t c o d e i s c o r r e c t .D o t h i s by checking the LED's against the Output Coding Table. You should have the next (secondfrom left) LED off (E),the next six LED's on and the last (far right) LED off. The Heep Test module has nine LED's.With the keyboard toward you, let's identify the LED's. Startingon the leftgoingto the right,the LED'sareas follows: C. The next LED monitors and represents 26 output codes, D. the next monitors and represents25 output codes, E. the next monitors and represents2a output codes, ENGC'E'EFI 8. 9. 10. Perform NORMAL mode test. With the keyboard in NORMAL (press and release S H I F Tt o e n s u r e t h a t k e y b o a r di s n o t i n S H I F T L O C K ) d e p r e s st h e k e y so n e a t a t i m e a s c a l l e d out in the Output Coding Table. Verify the output codes from the Heep Test Module by checking against the Output Coding Table Perform SHIFT mode test. Depress the S H I F T L O C K k e y a n d r e l e a s e .Y o u a r e n o w i n S H I F Tm o d e D e p r e s st h e k e y s o n e a t a t i m e a s called out in the Output Coding Table.Check t h e o u t p u t c o d e r e s p o n s ea s c a l l e d o u t i n t h e t a b l e a n d a s i n d r c a t e db y t h e L E D ' so f t h e H e e p Test Module. P r e s s S H I F T k e y a n d r e l e a s e .T h i s t a k e s y o u out of shift mode. Disconnect the +S-volt DC power f rom pin 1 of Heep Test Module. Disconnect the ground return from pin Z of the Heep Test Module. Remove the Heep Test Module from the Printed Circuit Board. l I @ ASCII ENGclElEFI O U T P U TC O D I N G T A B L E T h e O U T P U TC O D I N G T A B L E i s d i v i d e d i n t o t w o m a j o r s e c t i o n s- N O R M A L a n d S H I F T I n N O R M A L , t h e l e f t - h a n d c o l u m n l i s t s t h e l o w e r c a s e s y m b o l so f t h e k e y b o a r d I. n S H I F T t, h e l e f t - h a n dc o l u m n l i s t st h e m a r k e d u p p e r c a s e s y m b o l s o f t h e k e y b o a r d o r u n m a r k e d s y m b o l a b b r e v i a t i o n so f t h e A S C I I C o d e . U n m a r k e d s y m b o l a b b r e v i a t i o n sa r e p r e c e d e db y a n a s t e r i s k( * ) i n t h e S Y M B O Lc o l u m n a n d a r e e x p l a i n e df o l l o w i n gt h i s t a b l e .T h e O U T P U TC O D E c o l u m n s a r e s u b - d i v i d e di n t o 8 s e c t i o n s- t h e s e b e i n g E , 2 6 , 2 5 , 2 4 , 2 3 , 2 2 , 2 1a, n d 2 0 .T h i s d i v i s i o n i s i n d i c a t i v e o f t h e e n c o d e r o u t D U t b i t s . t s e s i d ee a c h s v m b o l i s t h e A S C I I c o d e f o r t h a t s v m b o l . T h e r i g h t - h a n d c o l u m n s l i s t t h e e q u i v a l e n th e x a d e c i m a ln u m b e r . I h NORMAL HEX O U T P U TC O D E SYMBOL E ,l SHIFT 26 2 5 24 23 22 E 2 1 20 HEX O U T P U TC O D E SYMBOL 26 25 24 23 22 2 1 20 o o 1 o 1 1 1 0 2E o 1 o o o o 1 21 o o 1 0 o o 1 o 22 U o 1 o n o 1 1 23 24 ESC q1 1 1 1 1 o 7E 1 Or o 1 1 o o o 1 JI 2 c o 1 I I 0 o 1 o 32 J o o 1 1 o o a I 1 33 4 o o 1 1 o I o o 34 s a o 1 o o 1 o o 5 0 o 1 o I o 35 o/ /o 0 0 1 o o 1 n 1 6 o o 1 1 o 1 1 o 36 & o 1 o o 1 1 o -l o o 1 1 o I 1 I o O 1 o I 1 I 8 o 1 1 o o o 0 o 1 o 1 0 o o o 1 1 1 o o o 1 o o 1 29 o jo o 1 1 o o o o 20 o 1 o I o o o 0 BACKSPACE BREAK TAB 1 I 3l 30 o 1 2D 1 1 0 1 o 3A o 1 I 1 o 5E o o 0 o o o o ,| o o o o 1 39 1 \ ( 38 I q 0 o o 1 1 0 08 * * o o 1 o9 28 1 0 0 o o o o o 1 1 1 1 o 1 3D :1. 0 0 1 0 1 o 1 0 2A SO o 0 0 o 1 1 1 o o o o 0 1 o o 1 1 o o o o o 60 0 o o o *BS o o o o o0 1 o o 27 0 SPACE *HT o I ,l 26 1 1 o o OE 0 08 1 09 15 ASCII NORMAL SYMBOL SHIFT HEX O U T P U TC O D E E 26 2 5 24 23 22 SYMBOL O U T P U TC O D E E 2 1 20 26 HEX 2 s 24 2 3 2 2 2 1 20 o o 1 o 1 o o o 1 51 * SOH o o o o o o o 1 o1 W o 'l o 1 o 1 1 1 57 * BEL o o o o o 1 1 1 07 E o 1 0 o o 1 o 1 45 * ENO o o o o o 1 o 1 o5 R o 1 o 1 o o 1 o 52 * STX 0 o o o 0 o 1 o o2 T o 1 o 1 o 1 0 o 54 * EOT 0 o o 0 1 o 0 o4 o 1 o 1 1 o 0 1 59 o o o o 1 o o 1 o9 o 1 o 1 o 1 o 1 55 o 1 o5 o 1 o o 1 o o 1 49 o9 o o 1 o 0 1 1 1 4F P o 1 o 1 o o o o t o 1 o 1 1 o 1 o 1 o 1 1 1 o o 5C *FF o o o o 1 o 1 o OA *LF DELETE 0 1 1 1 1 1 1 1 7F CTRL 1 0 o o 0 o 0 1 A o 1 o o o o o 1 41 S o 1 o 1 53 D o F 0 1 0 G 0 1 0 H o J K U L I N EF E E D 16 ENCCIEIEFI 1 'l HT * HT *sl 50 5B o1 ENO NUL 'y'T * * * 0 o o o o o 1 0 o o o 1 o o 1 o 0 o 1 1 1 OF o 0 1 o o o o o o oo o o o o 1 o 1 0 o o o I 1 o o OC 0 o o o 1 o 1 o OA 0 o 1 1 1 1 2F soH 1 o o o o o o 1 01 SOH o o o o o o o 1 ETX o 0 0 o 1 1 03 1 o o1 o 0 1 o o o 1 o o 44 EOT 0 o o o o 1 o o o4 0 o 1 1 o 46 * ACK 0 o 0 o 0 I 1 o 0 0 1 1 1 47 BEL 0 0 o 0 o 1 1 1 07 1 o o 1 o o o 0 o o o 1 o o o o 1 0 o 1 o 1 0 4A o o o o 1 o 1 0 OA 0 1 0 o 1 o 1 1 48 o o o o 1 o 1 1 OB 1 48 *BS LF +VT 0 o 1 OB 06 08 ASCII SHIFT NORMAL CODE OUTPUT SYMBOL E 26 24 23 22 2 1 o 1 o 0 1 1 o o o 0 1 1 1 o 1 1 3B @ o 1 o o o o 0 0 40 l 0 1 1 o 1 5D CLEAR 1 o o o o 1 0 o2 H E R EI S 1 o o n 0 o I 1 L BLANK "l o 0 0 0 Z o 1 o 1 X o I o \- o 1 V o B 1 0 1 4C *FF T CR * srx o3 - 1 o o o4 * I o o 5A 1 I o o o 58 0 o 0 o 1 1 43 ETX 1 o "l o 1 1 o 56 n 1 o o o o 1 o 42 N 0 'l 0 o 4E M U 1 o o 0 0 1 o o 0 SPACE R BLANK o 1 1 1 I 1 o o 1 1 o o 1 o 1 1 o 1 0 1 1 0 o 1 o o 1 o 0 o o 1 1 I 2', 23 22 2 1 20 1 1 o o oc o o I o 1 o 1 o 1 o o 0 o o 1 1 28 60 o o o 0 1 1 0 1 OD o o 0 0 1 o o2 n o o 1 1 1 1 EOT 1 0 U o o o o o3 1 o o o4 o o o o 1 U 1 o o o o o I o 0 o o8 o o o 0 n o 1 1 03 ACK o o 0 o 1 1 o 06 STX o o o 0 o 0 1 o UZ *BS *so 4D 25 o o o o ETX LF * HEX O U T P U TC O D E SYMBOL 2( 25 ,l I lo HEX E 26 L ENGc'ElEFI CR 0 o 0 0 o o OA 'l 1 1 0 OE 0 1 1 o 1 OD o o 2C o o 1 1 1 1 o 0 3C 1 0 2E o o 1 1 1 1 1 0 3E 1 1 2F o o I 1 1 1 1 1 3F tJ o 20 o o o o o 0 U U o 1 1 0 1 05 o5 7 * NUL * ENO 1 0 0 0 0 oo 17 ASiCII ENCCIEIEFI OUTPUTCODINGTABLE The following is a definitionof symbolabbreviationsof ASCIIcode in the SHIFTmodeof the OUTPUTCODING TABLE.Physicallythe keysare not identifiedas such.They are the samekeysthat are usedin the NORMAL mode. NORMAL mode key labelsare noted in bold face type. ESC = ESCAPE SO = SHIFTOUT n BACK SPACE BS = BACK SPACE TAB O, CTRL, A W. G R B L A N K ,E , U TAB HT = HORIZONTAL SOH=STARTOFHEADING BEL= RINGSTHE BELL E N O= E N O U I R Y B.R, CLEAR STX = STARTOF TEXT HERE lS, C, S ETX= END OF TEXT L BLANK, T, D EOT= ENDOF TRANSMISSION O S l = S H I F Tl N (SPACEP I NUL=NULL W=VERTICALTAB [,K /, L FF = |ORM FEEDTO TOP OF NEXTPAGE Z, LINE FEED,J LF = LIVEFEED V,F ACK=ACKNOWLEDGE M, ] CR = CARRIAGERETURNTo NOTES: 1. Left and right SHIFT,SHIFTLOCKand REPEATkeys are only used for internal control of logic circuits.No output codesare available. 2. Key n actuallyoutputs I eSCtt coding.. 3. The following six keys do not have an ASCIIcoding: BREAK,CTRL,CLEAR,HERElS and two unmarkedkeys.Thesekeys may be used as control keysfor externalf unctions.Referto How to Use E Output in the Theoryof Operationsection. 18 ASiCII TROUB LESHOOTING Negativeor FalseASCII: lf you checkedyour KeyboardEncoderby connecting it to a TV typewriter and typed RADIOSHACK and obtain the following W display:-)i 60*,7) <4 insteadof RADIOSHACK,troubleexistsbetweenthe Encoder and the equipment it is connectedto. Incorrectdatasuchas this indicatesthatthe Encoder is supplyingtypeddata into a systemthat isdesigned to acceptASCIIin a code oppositeof that which you have connected into it. Notice that the Encoder providesboth true and false ASCIIdata. lf the typed wordsare displayedlikesymbolicnewsprintcursing, then you confusedyour outputs.The ASCIIcodefor (HEX41 ).Thisis in trueform. the letterA is 1O0OOO1 Somesystemsrequirea false statement.A "false" A is in code01 1 1 1 1O,or HEX3E.lf you pressthe keyA and a " >" is printed, then you have reversedthe ASCIIstatement.All ASCIIoutputpins are marked. For example,20 or F, or 25or 2d.The symbolfortrue ASCIIoutputsis a number2 with a powerexponent that does not have a bar over it. In otherwords,20is a true statement.A false statement is shown with a bar. 26 is a false statement.The output codingchart shows true ASCll. lf you want to know what the false 's. 's ASCIIcodeis, changeall 1 to 0's and allO'sto1 lf the system requires false ASCII data, use outputs with a bar over it. lf the system requirestrue ASCII data, use outputswithout a bar. ForfalseASCIIdata, use connectorpins L, P, R, U, B, E, F and K. Fortrue ASCIIdata useconnectorpins M, N, S, T, C, D, H, and J. Construction Problems: lf you haveproblemswith the Encoderand you know it is connectedto the systemproperlyand the proper code source is selected,then you must troubleshoot the Encoder.Firstensurethat all integratedcircuits (lC's) are installedproperly.Pin 1 of all lC's are positionedto the left when viewedwith the keyboard toward you. Second.ensure each lC is in its proper mounting place. lt's easy to install a RS74OOin the RS74O2 position.They look the same and only their part n u m bersare different.In otherwords,makesurethat 27 is in Z7's placeand not somewhereelse.Noteon the Schematicthat Z1 looksexactlylike 213 or 22. They even have the same functional pin outputs. ENGC,EIEFI Lookingat the lC list at the bottomof the schematic, n o t e t h a t z 1 i s l i s t e da s R S 7 4 H 1 0 3a, n d 2 2 a n d 2 1 3 are listedas RS7473.lf you installaRS7473intoZl',s place, the ST (strobe) output will not operate correctly. Do not substitute a Rs7473 for a RS74Hl O3. lt's all rightto put a RS74H103inZ2or 23 position,but don't put a RS7473 in placeot Z1l Third,checkthat C2 and C3 capacitorsare installed correctly. capacitor c3 forms the systems master oscillator, while C2 performs a power-up clear function. Note that the two Tantalumcapacitors(C2 and C3) havea color dot on them. When facingthe dot, the positiveterminal is on the right side of the capacitor.Thesecapacitorsare electrolyticand must be properlyinstalled. Fourth,checkfor solderbridgesor shortsbetweenlC pins (an easy place for a short to form) or shorts between copperruns. Checkfor cold solderjoints.A cold solder joint is the most common soldering problem. Sometimes the joint feels strong, but electricallythey are deador open.A coldsolderjoint is usuallydull gray in colorand grainy.A goodjoint is bright and shiny. A cold solder is due to applying solderto the solderingiron ratherthan the junction. The solder flows off the tip and surroundsthe componentleadon its pad.Sincethe leadandpadare not up to solderingtemperature,the solder cools quickly and gives a bad, ugly joint. The oppositeof a cold solder joint is a burnt or broken printed circuit run. The copperon a PrintedCircuit Boardis applied by heatand heatcan take it rightoff again.TheASCII Encoder Project Board is double-sided, with plated-throughholes.Notethereare copperruns and pads on both sidesof the board.lt is not necessaryto apply solderto componentson the top (component) side of the board.Soldercomponentson one side of the board only. Each hole has copper plating completely through it and makes electrical connectionon both sidesof the board. Excessiveheat can lift a pad, breaking its plating and, therefore. opening partof the circuit not visibleto you. lf you f ind that a hole has opened, repair it. Suck out all the solderin the holeand inserta fine pieceof wire allthe way through the hole. lf an lC or the keyboardis on the otherside,push wire intothe holeas far as it will go. Leavea 1" tail on the wire on the backsideand apply solderto the wire and the lead.Melt the solder on both the wire and the componentlead.Capillary actionwill suckthe solderupthroughthe hole.When the solder has cooledlay the free end of the wire on 19 ASiCII the brokencopperrun or the pad and solderit. Cutoff the excesswire. Once you have confirmedthat you have repairedthe hole,protectthe wire and looserun or the pad with epoxy or some non-conductive cementor glue. Step-by-Step Troubleshooting: Thereare four main stepsin troubleshooting: Step 1. Step 2. Step 3. Step 4. Verifythe problem. lsolatethe problem. lsolatethe component. Repairthe problem. Step 1. Verify the Problem. Step 1 is easy.You have been doing just that. Now that you know the problem exists and is real, move to step 2. Step 2. lsolate the problem. To isolate the problem you must know the system. Read the detailedTheoryOf Operation.After you haveread it, read it again and study it. There are seven main sections to the ASCII Keyboard Encoder. ls the problem a Scanning problem? ls it a Keyboard problem?ls it a Key PressedDetectorproblem?ls it a Latch problem?lsolatethe section.For an example, let's saythe keyboardis puttingout goodcodesuntil a number key is pressed.Pressa letterand everything is fine, then press a number key and nothing happens.What's wrong? lt can't be the Scanner becausethe Scanner controls all keys,not just the letter keys. lt could be that on the keyboardevery number key is bad. Most likelythe problemis along the Keyboardline marked"c" or anythingline "c" feeds.This includesresistorR6,NANDgatesZl8 and 217. You have now isolatedthe problemto a logical area. Now move to step 3. Step 3. lsolate the component. Youmust isolate the componentthat is causingthe problem.Notethat ENGC'E'EFI the colonand semi-colonkeysare alsoon line "c" .lf these keys are pressed and the proper output is provided,the problem is probablya broken printed circuit foil path or an open feed-through.lf the system is still defective,check the Vcc junction of resistorR6. ls 5 volts present?lf it is. checkthe other side of RGfor 5 volts.lf 5 volts is here,pressa number key. Did the voltagedrop?lf it did.pressthe restof the number keys.lf everynumber keyproducesa voltage changeat junction"c" of RGwhen pressed.then the Keyboardis okay and so is R6. A rare problem is a shortedresistorR6 or a soldersplashwhich would not allow the voltageat line "c" to drop.Thebestway to check this problemis to use a logic analyzeror oscilloscopeinsteadof a voltmeter. Since nothing happens on the output connector when a number key is pressed,the problemmust be within the Key Pressed Detector. You have eliminatedthe Keyboardand R6 as the problem. What next?Lookingat the Schematicyou seethat the Key PressedDetector (21) is fed by 218, part of 215 and part oI 214. Keyboardlines "a", "b", "d", "e", "f" and "9" are satisfactorybecause when keys associatedwith these lines are pressed,an output is produced.This leavespin 5 of Zl 8. Lookingat pin 5 of 218 you find that the pin is bent and is not even soldered! You have isolated the component. Now move to step 4. Step 4. Repair the Problem. Step 4 is easy to implement.You straightenthe pin and carefully insert it in the proper hole and solder it. Checkto make sure the encoderworks properlynow. lf it does, your work is finished. lf the problemstill exists,you must replace218 since there is an internalopen withinthis lC. Thefollowingchartwill helpyou isolatethe problems and specificcomponent. TROUBLESHOOTING CHART IC 20 MAJOR SECTION P R O B A B L EC A U S E / I N D I C A T I O N z1 Key pressed detector 1 . Strobe (ST)output never changesstates. 2 . Strobe output cycles(repeats)whenkey pressed. z2 Keyboardscanner 1 . Outputs never change. 2 . Keyboardnot scanned. 3 . Problemwith key presseddetector. ASICII IC MAJOR SECTION ENCC'EIEFI P R O B A B L EC A U S E , / I N D I C A T I O N 23 Keyboardscanner 1 Outputsneverchange. 2 Keyboardnot scanned. 3 Defectiveboard. 24 Output latches 1. The four ASCIIoutput bits 20,21,22,23 neverchange. Z5 Output latches 1. The three ASCII output bits 24, 25,26 never change. ZG Keyboardscannerand encoder 27 Keyboardscanner,key pressed detector,and encoder ZB Encoder Zg Shift logic 1 . Defective board (does not oscillate). 2 . Problems with output bits 25 or f1 1 Problemwith output bits 24 and 26. 2 Problemwith strobeoutput and repeat. 3 No output when key pressed. ' t . Problem with output bits 23 or 24. 2. lncorrect shift coding on bits 2a or 25 1. Problem with output bits 2a or 26. 2. Incorrectshift coding on output bits 24 or 25. Z1O Repeatlogic,encoder,shift logic and key presseddetector 1 No repeatfunction. 2 No ST output. 3 No shift codes. 211 Repeatlogic 1 . Problemwith stobe output. 2 . No repeatfunction. 212 Kevboardscanner 1. Deadboard. 2. One or more columnsdead. 2 1 3 S h i f tl o g i c 1 . Shift problem. 2 . shift lock problem. 214 Key presseddetector,latch and shift logic 1. Problemwith key presseddetector. 2. Problemwith output latches. 3. Problemwith shift logic. 215 Key pressedlogic and shift logic 1. Problemwith key presseddetector. 2. Problemwith shift logic. 2 1 6 S h i f tl o g i c 1. Problemwith shift logic. Z17 Encoderlogic 1. Problemwith encoderlogic. Z18 Key presseddetector 1. Problemwith key presseddetector. 21 ASCII THEORYOF OPERATION The following is a detailedTheoryOf Operationof the ASCII KeyboardEncoderand its associatedcircuitry. Referto the SchematicDiagramandWaveformChart while readingthis Theory. Scanner The Scannercircuitryis made up of 76,23, 22 and 212. Partof ZGis usedas the master oscillatorf or the rest of the system.23, togetherwilhZ,2,forms a base 18 counter. Z3 supplies BCD data to Keyboard Scanner Decoder 212 and generatesthe four least significantdigits of the ASCII code. 22 supplies "housekeeping"pulsetrains(signalsthat contribute to proper operationof the system)for use during Keyboard Disable Time. Operationof the Scanner circuits is rather straight forward.26 oscillatesatapproximately 1 kHzwiththe components(c3 and R2) as shown. Lookingat the WaveformChart, the pulse train at line A is what couldbe expectedat pin 8 of 26. Inverter,214 pins 1 and 2, inverts the clock pulse train and it looks like line B on the WaveformChart.This pulse train is appliedto z.3,a counter.While Z3 counts from O to 15, it appliesdata to 212 and to Ouad Latch24.The output lines of 212 go low for one clockcycle.For example,pin 1 of 212 goeslow during zerotime as shown on line C of the WaveformChart.Duringthe next clock cycle,pin 2 of 212 goes low as shown on line D of the chart. Line E on the WaveformChart shows the output on pin 17 of 212. The pulseson 212's output labeledD-0throughDTE lread "not DO through not D15") and specificallythe clock(CLK) time during these output pulses are called "Keyboard Scan Time". Notice that outputs O through 15 are tied to the Keyboard.During Keyboard Scan Time, one of these outputs is low and the Keyboardis being scanned. As previouslymentioned,there is a time when the Keyboardis not scanned.This housekeepingtime is labeled KEYBOARD DISABLE time on the WaveformChart. Notice,on the WaveformChartthe relationship between lines E, F and G. When DT-S goesbackhigh counterZ3 is in transistionf rom count 15 to count 0. This transitionperiodcausesthe high at pin 12 of 22, as shown on WaveformCharttine F. This pin stayshigh for one clockcycle.22pin l2 now causes22 pin 9 to go high for one clockcyclewhich is 22 ENCC'E'EFI shown on line G of the chart.Thattime when either 22 pin 12 or pin 9 is high is calledKeyboardDisable Time. Noticethat lineH is highwhenevereitherZ2pin12or pin 9 is high. Line H showsthe outputof 27 pin 11. During this high logic level,Z3is commandedto ignore clock pulseson its input, pin 5. 212 is also disabledpreventingany of its outputpinsfrom going low during Keyboard Disable Time. Keyboard and Key Pressed Detector The Keyboard consistsof 63 keys,electricallywired into a matrixof 16 columnsby 7 rows.The columns are connectedto KeyboardScanner,212,while the rows are connectedto the KeyboardDetector and to the Row Encoder.The Detector consistsof 218 and 21.The Row Encoder,which will be discussedlater. consistsof 217. The operationof the Key PressedDetector, as its name implies,detectswhen a key is pressedon the Keyboard,and gives an indicationto the external circuitry that new data has been sent to the data latches. Each Keyboardcircle on the schematic,which is a representationof the Keyboard,consistsof a single pole.singlethrow, normallyopenswitch.Onesideof the switch is connectedto a column, and therefore 212. The other side of this switch is connectedto a row line, and thereforeto one of the inputsof 21B. Whenever a key is pressed.the switch is closed which makes an electicalconnectionfrom one of 212's outputstoone of the inputsof 218.Sinceoneof 212's outputs is low during Keyboard Scan Time, t h a t l o w i s a p p l i e dt o Z 1 8 .A l o w o n p i n s2 , 1 , S o r 4 o t 2 1 8 w i l l c a u s ea h i g h a t p i n 6 . A l o w o n p i n s 1 3 , 1 2 , 1 Oo r 9 o f 2 1 8 w i l l c a u s ea h i g ha t p i n 8 . S i n c ea l l r o w s of the Keyboardare connectedto 218. when any key is pressed.eitherpin 6 or pin 8 of Zl8will go high.pin 6 of 218 is connectedto pin 8 of 215. Pin 8 of Zl8 is connectedto pin 9 of 215.215 and part of 214 are connectedin such a way that a high is outputtedby 214. pin 1O,wheneverZlSoutputsa high.Theaction of a key pressed(switchclosure)placesa low at 218's input as shown on line I of the WaveformChart.The resultinghigh on pin 1Oof 214 is shownon lineJ (the line fabeled"Z1pin 14",which isconnectedtopin1O of 2141.The high shown on line J starts the Key Pressed Detector action. ASCII Noticefine K on the chart.Zl pin 12 will go high on the fallingedgeof the cTRsignal.ThisFlip-Flopstores the Key Pressedcommand until the Keyboard is disabledduring Keyboard Disabled Time. During this time, on the rising edge of 22 pin 9, 21 pin 9 storesthe K line data.Thisstorageis shownon lineL of the Waveform Chart. Duringthe positivepulse shown on line G, the next time the 6iR signalgoeslow, Flip-Flop21 pin 12goes back low. lf the key is still pressedduringthe next KeyboardScan Time, 21 pin 12 will onceagaingo high. As a matterof fact, line K will repeatitselfso longas the keyis helddown.But,noticethat lineL on t h e c h a r ti s s t i l lh i g h .S o l o n ga s t h e k e yi s h e l dd o w n , l i n e L w i l l s t a y h i g h .T h e h i g h o n l i n e L , c a u s e st h e repeatcounterto clear.lt also causesthe "Strobe" l i n et o g o h i g hw h i c h r e m a i n sh i g hs o l o n ga s t h e k e y is held down. When the key is released,during Key Released Time, Z'l pin 9 goes back low during Keyboard DisableTime. When this happens,the Strobeline goes back low, and the Keyboard is readied for anotherkey closure. Encoder The last three bits of the ASCIIcodeare encodedby hardwire logic. 217 forms the encoderfor these bits.Whenevera keyis pressed,a low pulsef rom212 i s r o u t e dt o Z l T . A n y t i m ea l o w i s s e n s e do n t h e i n p u t of 217, one or moreof its outputswill go high.Notice on the schematicthat each Keyboardrow is labeled with a lower case letter. Find row "a" on the schematic.This row hasthe BACKSPACE.TAB,and LINE FEEDkeys connectedto it. Followline "a" up until it ends.Noticeit only goesto the Key Pressed Detector and not to EncoderZ17.fhis meansthat if any key is pressedon the "a" line, the Key Pressed Detector will operateas mentionedbefore,but the outputsof the Encoderwill not change.lf you follow row "b", which has the SpaceBarand negativesign keys on it, you'll find it too goes to the Key Pressed Detector, but it also goesto 217 pin 10. When any k e yo n t h e " b " l i n ei s p r e s s e da, l o w p u l s ef r o m Z l 2 i s r o u t e dt o Z 1 7 p i n 1 0 ,w h i c h m a k e sp i n 8 g o h i g h .T h e followingtable shows the relationshipbetweenthe row inputsto the Encoderand the resultingoutputs. ENCC'EIEFT I N P U TT O D E C O D E RDECODER {217}OUTPUT ROW IABEL a b c d e f g PIN 6 PIN 8 PIN 12 ooo 010 011 100 101 "t11 ooo Shift and Shift Lock Circuitry The Shift and Shift Lock circuitry consists of Flip-Flops713, partof NOR GateZ15,and the Shift Modify networkconsistingof NAND Gates28,29, and Z7 and the otherhalf of 26. BasicallyZ15 stores the Shlft and Shift Lock instructions while the other gates mentionedmodifythe three most significant bits of the ASCII code to give a shifted character. Noticeon the Keyboardthat someof the symbolsand numbershave other symbolsprintedone abovethe other. In the normalor unshiftedmode,the codefor the lower number or symbol is printed.When an upper case symbol is needed,a Shift or Shift Lock operation must be performed. The difference between a Shift and Shift Lock is rather minor. To shift a character,you must hold down the shift key beforeor at the same time as you pressthe desired key. In Shift Lock, the shift modeis acruatedall the time. To unlockthe Shift Lock, you must pressand releaseone of the two shift keys. A Shift operationoccurswhen one of the two shift keys are pusheddown. Noticethat one side of the shift keys are tied to groundwhile the other side is tied to Z'14 pin 5. When the key is pressed,pin 5 of 714 goeslow which causespin 6 to go high. The c-lx p u l s et r a i nc a u s e s Z l 3p i n l 2 t o g o h i g h . P i n12 s t a y s high as long as one of the shift keysis helddown. lf pin 12 will go backlow.Assuming the key is released, the shift key is held down, pin 3 of 215 will be high. Z15 controlsthe lowergates.When its outputis high a normal or unshiftedmode is selected.When its output is low, a shiftedmode is selected.Any highon input of 215 causesits outputpin,pin 1, to go low.A Shift operationthereforecauses215's outputto go low. 23 ASCII In the normal mode,a high out of 215, pin 1, causes Z9 and Z8 to be disabled.This causesdata, listed in the encoder table, to be routed to the two NAND Gates,27 and the other half of 26. The data is then sent to the three data latches in 25. In the shifted mode,215 pin 1 is low, which disables the three NAND Gatesin 216. NANDGatesZ9 and Z8 now become active.Thesethree Gates do two major things. First they decode incoming data. Secondly, they modifythe three higher ASCIIbits, if the proper conditions are met. One Gate will be analyzedto show you the operationof these Gates.In order for pin 8 of Z9 to go low, four conditionsmust be met. First,217 pin 12 mustbe low.Second,217pin 8 must be low. Third, there must be a Shift command. Fourth, one of the keys in the "O" column must be pressed.Lookingat the decoderchart, we find three rows will be encodedto producea low on pin 12 and pin 8 at the sametime. Theencoderrows are "a" , "d" and "9". Lookingatthe KeyboardMatrix,there is only one key in the "O" colu-mn that has a shifted character,that being tfre "d" key.Therefore,when you pressthe @ key and a shift (or shift lock)key,you will meet the four conditionsnecessaryto causeZ9 pin 8 to go low. When this pin goes low, the outputat 27 pin 6 and 26 pin 6 will go high. What happensin terms of code modifyingis the three higherorderbits of the ASCIIcodefor @ (1O0)willbe modifiedto be the three bit codefor the "r" symbol(11O). The following Tableshows row linecodesat the latch inputs during the Normal and Shifted mode. (NORMAL) UNSHTFTED 27, Pin 6 26, Pin 6 27, Pin 3 SHIFTED 27, Pin 6 *Only during 1 10Othrough 1 1 1 1 of the 4 least significantbits **Only during OOOO of the 4 least significantbits 24 ENCC'E EFI 26, Pin 6 27, Pin 3 @ ASCll The shift lock circuit modifies the codes just as the shift function. The method of holding the shift lock instructions is slightly different in Flip-Flop213. W h e n t h e " S h i f t L o c k " k e y i s p r e s s e d .F l i p - F l o p2 1 3 pin 9 goes high. When the Shift Lockkey is released, p i n 9 o f 2 1 3 s t a y s h i g h . T h i s F l i p - F l o ps t a y s i n t h i s state until one of the Shift Keys is pressed At that t i m e , p i n 9 w i l l g o t o O , a n d u n l o c kt h e S h i f t f u n c t i o n . N o t i c et h a t t h e S h i f t L o c k i s t i e d t o Z 1 5 i n t h e s a m e m a n n e r a s S h i f t f u n c t i o n . T h e r e f o r e ,i t o p e r a t e s t h e Shift circuitsin the same wav. Repeat Circuitry The RepeatCircuitrycounts the number of Keyboard scans and pulsesthe Strobe output Z11 is a counter which provides a square wave output to Strobe NAND Gale 27. The counter counts 16 Keyboard scans for a cycleof the strobeoutput. lf the CLK is set a t 1 k H z ,t h e n t h e f r e q u e n c ya t p i n 5 o f 7 1 1 i s 5 5 . 5 H z . T h e f r e q u e n c yo I 2 1 1 p i n 7 i s 3 4 7 H z , w h i c h i s t h e specified Repeat rate. l f y o u w i s h t o i n c r e a s et h e s c a n r a t e , y o u c a n r e p l a c e capacitorC3 with a 1 pF cafacitor. You may further experiment with other capacitor values to satisfy y o u r i n d i v i d u a lr e q u i r e m e n t s . ENCC'EIEFI turn sends a store command to the output latches Whatever data is present at the "D" inputs of the o u t p u t l a t c h e s ,w h e n i t s c L K i n p u t g o e s h i g h , w i l l b e stored and outputted at the O and O pins How to Use E Output The E output is used for keys that have no ASCII c o d i n g . T h e r e a r e s i x o f t h e s e k e y s ; B R E A K ,C T R L , C L E A R ,H E R El S a n d t w o u n m a r k e d k e y s .T h e s e k e y s may be used as control keys for externalfunctions A code is assigned to these keys to allow them to be o u t p u t t e d o n t h e s a m e b u s s a s t h e A S C I I c o d e s .T h e E output allows external decoding of these keys T w o a p p r o a c h e sc a n b e u s e d t o a c c o m p l i s ht h i s O n e m e t h o d i s s h o w n i n F i g u r e5 . f h e 7 4 4 2 r e c e i v e s t h e l e a s t t h r e e s i g n i fi c a n t b i t s o f t h e o u t p u t l a t c h e s f r o m t h e k e y b o a r d .W h e n E g o e s l o w , t h e 7 4 4 2 g i v e sa l o w o n o n e o f i t s o u t p u t s .T h i s i s inverted by one of the 74O4's and applied to one of the J inputs of the 7473 flip-flops. When the key is r e l e a s e d ,t h e S T l i n e g o e s l o w a n d s e t s t h e O o u t p u t of one of the flip-flops which in turn powers some external logic.lf we want to clear all of the f lip-flops, t h e C L E A Rk e y m a y b e p r e s s e dw h i c h r e s e t sa l l o f t h e 7473's when that kev is released. Output Latches The Output Latches, 24 and 25, store the 4 bit c o l um n c o d e f r o m 2 3 , a n d t h e 3 b i t r o w c o d ef r o m t h e E n c o d e r , t o f o r m t h e A S C I I C o d e .W h e n e v e r a k e v i s pressed, the Key Pressed Detector sends a pulse to 2 1 6 p i n 1 . T h i sp u l s e i s N A N D e dw i t h t h e C L Ka n d i t i n RS740/t Another method to allow the E output to provide external decoding of the keys is shown in Figure 6. T h i s m e t h o d u s e s t h e e c o n o m i c a l 7 4 O OO u a d g a t e s a s l a t c h e sa n d a 7 4 O 4 i n v e r t e ri s n o t u s e d .l t r e s p o n d s t o a k e y i m m e d i a t e l y s i n c e t h e S T k e y b o a r do u t p u t i s not used. RS7400 157173 I O E X I E R N A If.U N C T I O N S I O E X I E R N A I I. U N C I I O N S F I G U R E5 . E X T E R N A LD E C O D I N G ( M E T H O D1 ) F I G U R E6 . E X T E R N A LD E C O D I N G ( M E T H O D2 ) 25 r I I I I N o @ prlru^L^-' I KEYBOARDI DTSABLE I KEY PRESSED BOt2 ol23t5A 15A lrllll I A rlll crK -,rl-fL,rL,r\Wpt-t-,rLrt-,r\FfL_J-LJ-t-f\ c B crK --r-lfi-t--rtffi m c 66', J D DI o ! D!s € m 'n F z2prNr2 o v 3 o G z2PrNe I H z?PrNrr I zrgPrN. ---{ T { J zrPlN 14 H rl I BO15ABO r1 8ot5AB ltrlr tr-rr-rrnrth-,r-rnnn \-n-,nJl.d h-l--].r-t-J h-r-lF-l-t-t Ft-r--r h-r- r-til Fl-,(-t hf f-\ Tl 1.(-l----fFl-l--f K zrprNr2 F---|-|_1ts-+t+ L zrprNe l M z16PtN 3 tsA rtlltl \fuLrt l+F-J--1-{I--J--_1-ft-tf+'r-l-t lt ll +t--l-t{F--J-\t--5lf\--f - KEYRETEASED 1-1 -I#F-L+ID o g m z o 0 o Il ! ( EOGT C0illtCTOB- ?1,,,-n, .lE 26 -lI OF ^ l/- c , 4 Ir '{' 25 25 ,l'./ ge llow' 0 vcc A S C irl ( E Y 8 0 A Rt C 0 ',S USr t { 0 T t s u t { r t s so r H t n w r sst P r c rrft 0 I A [ [ N E S I S T O RASB E I / 4 W A T T txP8tssrD tr{ oHMs lx = 10001 2 ARE II{ MICROTARAOS CAPACIIONS {9f = PIC0fARADS) Rtf DTS zr 22, zr3 2 3 ,z f l 2 4 .z 5 26 z?,216 28,zD 2 9 .z l 8 z l 0 ,z r 4 212 zts Vcc I C I Y P T Ptil lr0 4 Rs74Ht0t 4 Rs7473 t6 nst4rg3 ns1475 5 t4 RS74t3 t4 RS7400 t4 RS74l0 Rst420 t4 Rsl404 t4 BSt4l54 24 l4 Rs7402 SPANEGATE . F I G U R E8 . A S C I I K E Y B O A R DE N G O D E RS C H E M A T I CD I A G R A M i+J\ '402 Gl{0 P|l{ ilo ll ll 8 12 I I I 1 7 12 1 --fi>'sov lrA, f t 0l --Doov )\' i )