apple2_mockingboard/docs/mockingboard_table_access_routine.assy.txt

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2017-04-15 18:09:24 +00:00
;TABLE ACCESS ROUTINE
;FOR SLOT 4
*
ORG $8000
;ADDRESSES FOR FIRST 6522
PTR EQU $08 ;DATA POINTER
ORA EQU $C401 ;PORT A
LATCH EQU $900B ;LATCH SUB-ROUTINE
WRITE EQU $9016 ;WRITE SUB-ROUTINE
RESET EQU $9021 ;RESET SUB-ROUTINE
;ADDRESSES FOR SECOND 6522
PRT2 EQU $0A ;DATA POINTER
ORA2 EQU $C481 ;PORT A
LATCH2 EQU $9037 ;LATCH SUB-ROUTINE
WRITE2 EQU $9042 ;RESET SUB-ROUTINE
RESET2 EQU $904D ;RESET SUB-ROUTINE
*
*ROUTINES FOR FIRST 6255
*
START JSR RESET ;RESET SOUND CHIP
LDY #$00 ;USED TO IDENTIFY REGISTER
LOOP STY ORA ;# OF SOUND CHIP
JSR LATCH
LDA (PTR),Y ;GET DATA FROM TABLE
STA ORA
JSR WRITE ;STORE IN REGISTER
CPY #$0F ;END OF DATA?
BEQ DONE ;YES, EXIT
INY
JMP LOOP ;NO, GET NEXT SET
DONE RTS ;RETURN
*
*ROUTINES FOR SECOND 6522
*
START2 JSR RESET2 ;SAME INSTRUCTIONS AS
LDY #$00 ;ABOVE
LOOP2 STY ORA2
JSR LATCH2
LDA (PTR2),Y
STA ORA2
JSR WRITE2
CPY #$0F
BEQ DONE2
INY
JMP LOOP2
DONE2 RTS