MULTIPLEXER
;*****************************************************************************
;* MODULE-MUX-V00.ASM
;*****************************************************************************
;* NAME ...................: MUX
;* VERSION ................: V00
;* PURPOSE ................: CONTROL ANALOG MULTIPLEXOR SELECT LINES
;* PROCEDURE ..............: SET/RESET 2 BITS IN PIA0
;* NOTES ..................:
;* COLOR COMPUTER 3 SERVICE MANUAL PP 9,
;* FF01:3 SEL 1 LSB OF THE TWO ANALOG MUX SELECT LINES
;* FF03:3 SEL 2 MSB OF THE TWO ANALOG MUX SELECT LINES
;* SNDEN SEL2 SEL1 SELECTS
;* 0 X X 1-BIT AUDIO
;* 1 0 0 6-BIT DAC JOYSTICK 0
;* 1 0 1 CASSETTE JOYSTICK 1
;* 1 1 0 CARTRIDGE JOYSTICK 2
;* 1 1 1 NO SOUND JOYSTICK 3
;*****************************************************************************
PIA0AD: equ $FF00 ; PIA 0 PORT A DATA
PIA0AC: equ $FF01 ; PIA 0 PORT A CONTROL
PIA0BD: equ $FF02 ; PIA 0 PORT B DATA
PIA0BC: equ $FF03 ; PIA 0 PORT B CONTROL
MUXSEL: rmb 1 ; MUX SELECT INPUT
MUX: pshs A,B,X,CC ; SAVE REGISTERS BEFORE WE MESS WITH THEM
lda PIA0AC ; GET CURRENT STATE OF PIA0 PORT A CONTROL
ldb PIA0BC ; GET CURRENT STATE OF PIA0 PORT B CONTROL
ldx MUXSEL ; ENTER WITH X FOR MUX CHOICE
cmpx #0 ; MUXSEL equal 0?
beq SELDAC ; 6-BIT DAC SOUND / JOYSTICK AXIS 0
cmpx #1 ; MUXSEL equal 1?
beq SELCASS ; CASSETTE SOUND / JOYSTICK AXIS 1
cmpx #2 ; MUXSEL equal 2?
beq SELCART ; CART SOUND / JOYSTICK AXIS 2
cmpx #3 ; MUXSEL equal 3?
beq SELNONE ; NO SOUND / JOYSTICK AXIS 3
puls A,B,X,CC ; MUXSEL EQUAL SOMETHING ELSE? JUST RETURN
SELDAC: anda #%11111011 ; SEL LSB = 0
andb #%11111011 ; SEL MSB = 0
bra ENDMUX ; GO SET THEM
SELCASS: ora #%00000100 ; SEL LSB = 1
andb #%11111011 ; SEL MSB = 0
bra ENDMUX ; GO SET THEM
SELCART: anda #%11111011 ; SEL LSB = 0
orb #%00000100 ; SEL MSB = 1
bra ENDMUX ; GO SET THEM
SELNONE: ora #%00000100 ; SEL LSB = 1
orb #%00000100 ; SEL MSB = 1
; FALL THROUGH TO
ENDMUX: sta PIA0AC ; SAVE OUT MODIFIED SEL LSB
stb PIA0BC ; SAVE OUT MODIFIED SEL MSB
puls A,B,X,CC,PC ; AND DONE
;*****************************************************************************
;* END OF MODULE-MUX-V00.ASM
;*****************************************************************************
RTS
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