Routines
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ED21: defer a command
ED21 85 95 STA $95 save as serial defered character
ED23 78 SEI disable the interrupts
ED24 20 97 EE JSR $EE97 set the serial data out high
ED27 C9 3F CMP #$3F compare read byte with $3F
ED29 D0 03 BNE $ED2E branch if not $3F, this branch will always be taken as after VIA 2's PCR is read it is ANDed with $DF, so the result can never be $3F ??
ED2B 20 85 EE JSR $EE85 set the serial clock out high
ED2E AD 00 DD LDA $DD00 read VIA 2 DRA, serial port and video address
ED31 09 08 ORA #%00001000 mask xxxx 1xxx, set serial ATN low
ED33 8D 00 DD STA $DD00 save VIA 2 DRA, serial port and video address
This entry point is used by the routines at EDB9 and EDC7.
if the code drops through to here the serial clock is low and the serial data has been released so the following code will have no effect apart from delaying the first byte by 1ms
set the serial clk/data, wait and Tx byte on the serial bus
ED36 78 SEI disable the interrupts
ED37 20 8E EE JSR $EE8E set the serial clock out low
ED3A 20 97 EE JSR $EE97 set the serial data out high
ED3D 20 B3 EE JSR $EEB3 1ms delay
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