SteveFosdick
commented
3 weeks ago Problem is possibly related to interrupts. The ISR for the M2 module is:
195C: 08 PHP
195D: 8A TXA
195E: 48 PHA
195F: A2 00 LDX #00 ; Point to first ACIA
1961: AD 08 FC LDA FC08 ; Did this raise the interrupt?
1964: 30 0E BMI 1974 ; Yes, handle it.
1966: E8 INX ; Point to second ACIA
1967: E8 INX
1968: AD 0A FC LDA FC0A ; Did this raise the interrupt?
196B: 30 07 BMI 1974 ; Yes, handle it.
196D: E8 INX ; Point to third ACIA
196E: E8 INX
196F: AD 0C FC LDA FC0C ; Did this raise the interrupt?
1972: 10 38 BPL 19AC ; No, end of this part of ISR.
; All three ACIAs end up here is one of them has caused
; the interrupt. X points to which one.
1974: BD 08 FC LDA FC08,X ; Get the status register.
1977: 29 02 AND #02 ; Check for Tx Data Reg Empty.
1979: F0 31 BEQ 19AC ; Branch if not empty.
197B: 98 TYA
197C: 48 PHA
197D: BD 3A 19 LDA 193A,X ; Anything to send?
1980: DD 39 19 CMP 1939,X
1983: F0 15 BEQ 199A ; Branch if nothing to send
1985: 18 CLC
1986: 69 01 ADC #01 ; Advance the buffer pointer?
1988: 29 1F AND #1F
198A: 1D 45 19 ORA 1945,X
198D: 9D 3A 19 STA 193A,X
1990: A8 TAY
1991: B9 D9 18 LDA 18D9,Y ; Get the byte to transmit.
1994: 9D 09 FC STA FC09,X ; Write to TX data register.
1997: 4C A4 19 JMP 19A4
199A: A9 15 LDA #15 ; Turn off the TXDR empty IRQ.
199C: 9D 08 FC STA FC08,X ; Write to control register.
199F: A9 00 LDA #00
19A1: 9D 3F 19 STA 193F,X
19A4: 68 PLA
19A5: A8 TAY
19A6: 68 PLA
19A7: AA TAX
19A8: A5 FC LDA FC ; End of ISR having done something.
19AA: 28 PLP
19AB: 40 RTI
19AC: 68 PLA ; End of ISR when daisy chaining.
19AD: AA TAX
19AE: A5 FC LDA FC
19B0: 28 PLP
19B1: 6C 0C 18 JMP (180C)
As per the Music 2000 user guide, setting a tune playing and then running:
Cause the voice concerned to no longer sound on the Music 5000 but does not cause any MIDI activity.