of Microprocessors

310 MUSICAL ApPLICATIONS OF MICROPROCESSORS
0164 FCDO DOCE BNE SCNREN RE-ENTER SCAN LOOP
0165 FCDF 9B STATIC TVA OUTPUT A KEY PRESS EVENT
0166 FCEO 0980 ORA #$80 FIRST BYTE = KEY 10 NUMBER, DEPRESS
0167 FCE2 78 SEI DISABLE TIMER INTERRUPT WHILE OUEUEING
0168 FCE3 A63D LOX QUIP GET QUEUE INPUT POINTER
0169 FCE5 953F STA EVQU,X STORE FIRST BYTE
0170 FCE7 B90000 LOA MKYBST,Y GET KEY STATE
0171 FCEA 4A LSR A ISOLATE AND RIGHT JUSTIFY VELOCITY COUNT
0172 FCEB 4A LSR A
0173 FCEC 9540 STA EVQU+1,X ; OUTPUT AS SECOND BYTE OF EVENT
0174 FCEE A55F LOA TIME ; GET LOW BYTE OF TIME
0175 FCFO 9541 STA EVQU+2,X ; OUTPUT AS THIRD BYTE
0176 FCF2 A560 LOA TIME+l ; GET HIGH BYTE OF TIME
0177 FCF4 9542 STA EVQU+3,X ; OUTPUT AS FOURTH BYTE
0178 FCF6 8A TXA ; MOVE QUEUE INPUT POINTER UP 1 NOTCH
0179 FCF7 18 CLC
0180 FCF8 6904 ADC #4
0181 FCFA 291F AND #$IF WITH WRAPAROUND
0182 FCFC 8530 STA QUIP
0183 FCFE 58 CLI RE-ENA8LE INTERRUPTS
0184 FCFF A902 LOA #2 SET KEY STATE TO 2
0185 FOOl 990000 STA MKY8ST,Y
0186 FD04 DOA7 BNE SCNREN RESUME SCANNING
0187 FD06
0188 FD06
0189 FD06 B94004 STAT2 I.~A MKY8L,Y TEST KEY CONTACT WITH LOWER BUS
0190 FD09 10A2 8PL SCNREN RESUME SCANNING IF IN CONTACT
0191 FDOB A903 LOA #3 SET THE STATE TO 3 AND ZERO VELOCITY
0192 FOOD 990000 STA MKYBST, Y COUNT IF NO CONTACT
0193 FDI0 D09B BNE SCNREN AND RESUME SCANNING
0194 F012
0195 FD12
0196 F012 B94004 STAT3 LOA MKYBL,Y ; TEST KEY CONTACT WITH LOWER BUS
0197 FD15 3007 BMI STAnA ; JUMP IF NOT CONTACTING IT
0198 F017 A902 LOA #2 ; SET STATE TO 2 AND CLEAR VELOCITY COUNT
0199 F019 990000 STA MKYBST,Y ; IF CONTACTING LOWER BUS
0200 FDIC DD8F BNE SCNREN ; RE-ENTER SCAN LOOP
0201 FDIE B90004 STAT3A LOA MKYBU,Y ; TEST KEY CONTACT WITH UPPER BUS
0202 FD21 1010 BPL STAnc ; JUMP IF CONTACTING IT
0203 FD23 B90000 LOA MKYBST,Y ; IF NOT, GET KEY STATE AND INCREMENT THE
0204 F026 18 CLC ; VELOCITY COUNT
0205 FD27 6904 ADC #4
0206 F029 9002 BCC STAT3B SKIP IF NO OVERFLOW
0207 F02B E904 SBC #4 RESTORE MAX VELOCITY COUNT IF OVERFLOW
0208 FD20 990000 STAT3B STA MKYBST,Y
0209 FD30 4CADFC JMP SCNREN RE-ENTER SCAN LOOP
0210 FD33 78 STAnc SEI DISABLE TIMER INPURRUPT WHILE OUEUEING
0211 FD34 A630 LOX QUIP OUTPUT AN EVENT, GET QUEUE INPUT POINTER
0212 F036 943F STY EVQU,X STORE FIRST BYTE = KEY 10 NUMBER, RELEASE
0213 F038 B9OO00 LOA MKYBST,Y GET KEY STATE
0214 FD3B 4A LSR A ISOLATE AND RIGHT JUSTIFY VELOCITY COUNT
0215 FD3C 4A LSR A
0216 F030 9540 STA EVQU+! ,X OUTPUT AS SECOND BYTE OF EVENT
0217 F03F A55F LOA TIME GET LOW 8YTE OF TIME
0218 FD41 9541 STA EVQU+2,X OUTPUT AS THIRD BYTE
0219 FD43 A560 LOA TIME+! ; GET HIGH BYTE OF TIME
0220 FD45 9542 STA EVQU+3,X ; OUTPUT AS FOURTH BYTE
0221 F047 8A TXA ; MOVE QUEUE INPUT POINTER UP 1 NOTCH
0222 F048 18 CLC
0223 FD49 6904 AOC #4
0224 F04B 291F AND #$IF ; WITH WRAPAROUND
0225 F040 8530 STA QUIP
0226 FD4F 58 CLI ; RE-ENABLE INTERRUPTS
0227 FD50 A900 LOA #0 ; SET KEY STATE TO 0 (INACTIVE)
Fig. ~9. Listing of keyboard control program (cont.)