Hello All, It looks like the following snippet is the key part of the JD routine, which reads in data as bit-pairs every 10us. The trick of course is if this is to be replicated for a VIC20 or C16/Plus4 then the data needs to be processed in this relatively short time as there is no hand-shaking to hold off the 1541 once the Ok for the byte send has been initiated. Also, data is sent as 254byte packets... between pauses. Not knowing enough about either the VIC20 or the Plus4: 1) are the port locations of DATA and CLOCK signals as convenient as they are on the C64/C128? 2) the Plus4 runs at two speeds (?), is this controllable (since you wouldn't want to be switching speeds during such critical open-loop timing) beq $fb44 .fb4f lda $b2 ; lower three bits of $dd00 stx $dd00 ; store %00100xxx in $dd00 bit $dd00 ; bit test bvc $faf0 ; branch is input clk=0 nop ; timing sta $dd00 ; store %00000xxx in $dd00 ora $dd00 ; read two first bits lsr a ; move right two times lsr a nop ; timing ora $dd00 ; read next two bits lsr a ; move right two times lsr a eor $b2 ; "trixx" to handle the lower three bits of $dd00 eor $dd00 lsr a ; move right two times lsr a eor $b2 ; "trixx" to handle the lower three bits of $dd00 eor $dd00 cpy $93 ; load/verify flag bne $fb83 ; branch if verify sta ($ae),y ; store loaded byte in memory PLEASE TAKE NOTE: The contents of this email (including any attachments) may be privileged and confidential. Any unauthorised use of the contents is expressly prohibited. If you have received this email in error, please advise us immediately (you can contact us by telephone on +61 8 9441 2311 by reverse charge) and then permanently delete this email together with any attachments. We appreciate your co-operation. Whilst Orbital endeavours to take reasonable care to ensure that this email and any attachments are free from viruses or other defects, Orbital does not represent or warrant that such is explicitly the case (C) 2000: Orbital Engine Company (Australia) PTY LTD and its affiliates - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail email@example.com.
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