C64 ROM: Routine at FE72

FE72: RS232 NMI routine

Used by the routine at FE47.
FE72	98	TYA
FE73	2D A1 02	AND $02A1	AND with the RS-232 interrupt enable byte
FE76	AA	TAX
FE77	29 01	AND #$01
FE79	F0 28	BEQ $FEA3
FE7B	AD 00 DD	LDA $DD00	read VIA 2 DRA, serial port and video address
FE7E	29 FB	AND #%11111011	mask xxxx x0xx, clear RS232 Tx DATA
FE80	05 B5	ORA $B5	OR in the RS232 transmit data bit
FE82	8D 00 DD	STA $DD00	save VIA 2 DRA, serial port and video address
FE85	AD A1 02	LDA $02A1	get the RS-232 interrupt enable byte
FE88	8D 0D DD	STA $DD0D	save VIA 2 ICR
FE8B	8A	TXA
FE8C	29 12	AND #$12
FE8E	F0 0D	BEQ $FE9D
FE90	29 02	AND #$02
FE92	F0 06	BEQ $FE9A
FE94	20 D6 FE	JSR $FED6
FE97	4C 9D FE	JMP $FE9D
FE9A	20 07 FF	JSR $FF07
FE9D	20 BB EE	JSR $EEBB
FEA0	4C B6 FE	JMP $FEB6
FEA3	8A	TXA	get active interrupts back
FEA4	29 02	AND #%00000010	mask ?? interrupt
FEA6	F0 06	BEQ $FEAE	branch if not ?? interrupt
was ?? interrupt
FEA8	20 D6 FE	JSR $FED6
FEAB	4C B6 FE	JMP $FEB6
FEAE	8A	TXA	get active interrupts back
FEAF	29 10	AND #%00010000	mask CB1 interrupt, Rx data bit transition
FEB1	F0 03	BEQ $FEB6	if no bit restore registers and exit interrupt
FEB3	20 07 FF	JSR $FF07
FEB6	AD A1 02	LDA $02A1	get the RS-232 interrupt enable byte
FEB9	8D 0D DD	STA $DD0D	save VIA 2 ICR
This entry point is used by the routines at F92C, FA60 and FBCD.
FEBC	68	PLA	pull Y
FEBD	A8	TAY	restore Y
FEBE	68	PLA	pull X
FEBF	AA	TAX	restore X
FEC0	68	PLA	restore A
FEC1	40	RTI