Routines
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F483: initialise RS232 output
Used by the routines at F291 and F409.
F483 A9 7F LDA #$7F disable all interrupts
F485 8D 0D DD STA $DD0D save VIA 2 ICR
F488 A9 06 LDA #$06 set RS232 DTR output, RS232 RTS output
F48A 8D 03 DD STA $DD03 save VIA 2 DDRB, RS232 port
F48D 8D 01 DD STA $DD01 save VIA 2 DRB, RS232 port
F490 A9 04 LDA #%00000100 mask xxxx x1xx, set RS232 Tx DATA high
F492 0D 00 DD ORA $DD00 OR it with VIA 2 DRA, serial port and video address
F495 8D 00 DD STA $DD00 save VIA 2 DRA, serial port and video address
F498 A0 00 LDY #$00 clear Y
F49A 8C A1 02 STY $02A1 clear the RS-232 interrupt enable byte
F49D 60 RTS
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