of Microprocessors

ORGAN KEYBOARD INTERFACE 317
SERCTL $0800 6850 SERIAL I/O CHIP CONTROL REGISTER
SERSTS $0800 6850 STATUS REGISTER
SEROTA $0801 6850 TRANSMIT AND RECEIVE DATA REGISTER
------ - --- --- ------------ -----
INIT LOA #$17 INITIALIZE 6850 SERIAL I/O CHIP
STA SERCTL
LOA #$15
STA SERCTL
----. - ----- - - - ------------ ----
STATIC SEI DISABLE INTERRUPTS WHILE STORING EVENT
LOX QUIP OUTPUT AN EVENT, GET QUEUE INPUT POINTER
LOA #$90 KEY DOWN EVENT ON MIDI CHANNEL MIOICH
ORA MIOICH
STA EVQU ,X STORE I N QUEUE
INX INCREMENT QUEUE POINTER
CPX #$20 WRAPAROUND THE POINTER IF NECESSARY
BNE STATIO
LOX #0
STATIO TYA GET KEY NUMBER
CLC ADJUST TO MIDI STANDARD OF 60=MIOOLE C
AOC #60-24 THIS GIVES 2 OCTAVES BELOW AND 3 ABOVE
STA EVQU ,X ; STORE RESULT I N QUEUE
INX ; INCREMENT AND WRAPAROUND QUEUE POINTER
CPX #$20
BNE STATIE
LOX #0
STATIE STX QUIP SAVE QUEUE POINTER TEMPORARILY
LOA MKYBST, Y GET VELOCITY COUNT, RANGE 0-63
LSR A
LSR A
TAX LOOKUP APPROPRIATE MIDI VELOCITY
LOA VELTAB,X IN A TABLE
LOX QUIP RESTORE QUEUE POINTER
STA EVQU ,X STORE THE VELOCITY IN THE QUEUE
INX INCREMENT AND WRAPAROUND QUEUE POINTER
CPX #$20
BNE STATlF
LOX #0
STATIF STA QUIP STORE THE UPDATED QUEUE POINTER
eLI RE-ENABLE INTERRUPTS
LOA #2 SET KEY STATE TO 2
STA MKYBST. Y
JMp· SCNREN RESUME SCANNING
------ --- ---- - - ------ ----- - ---
STAnc SEI ; DISABLE INTERRUPTS WHILE STORING EVENT
LOX QUIP ; OUTPUT AN EVENT, GET QUEUE INPUT POINTER
LOA #$80 KEY UP EVENT ON MIDI CHANNEL MIOICH
ORA MIDICH
STA EVQU,X STORE IN QUEUE
INX
INCREMENT QUEUE POINTER
CPX #$20 WRAPAROUND THE POINTER IF NECESSARY
BNE STAnD
LOX #0
STAno TVA GET KEY NUMBER
CLC ADJUST TO MIDI STANDARD
AOC #60-24
STA EVQU ,X ; STORE RESULT IN OUEUE
INX ; INCREMENT AND WRAPAROUND QUEUE POINTER
CPX #$20
BNE STAT3E
LOX #0
STAnE STX QUIP SAVE QUEUE POINTER TEMPORARILY
LOA MKYBST, Y GET VELOCITY COUNT, RANGE 0-63
LSR A
LSR A
TAX LOOKUP APPROPRIATE MIDI VELOCITY
LOA VELTAB,X IN A TABLE
LOX QUIP RESTORE OUEUE POINTER
STA EVQU ,X ; STORE THE VELQCITY IN THE QUEUE
INX ; INCREMENT AND WRAPAROUND OUEUE POINTER
CPX #$20
8NE sTAnF
LOX #0
STAnF STA QUIP STORE THE UPDATED DUEUE POINTfR
CLl RE -ENABLE INTERRUPTS
LOA #0 SET KEY STATE TO 0 (INACTIVE)
STA MKYBST. Y
JMP SCNREN RESUME SCANNING
Fig. 9-12. Modified code segments for MIDI