From: Baltissen, GJPAA (Ruud) (ruud.baltissen_at_abp.nl)
Date: 2005-05-03 13:35:01
Hallo allemaal, Andre wrote: > Second: Indeed in the write block routine ($f575) the last > "BVC *" at $F5CA waits for the last data byte (from ($30),y) > to be _loaded_ into the shift register. (After studying the schematics) Yep, you're absolutely right. So it is not the end of the writing proces, but the beginning. > Immediately after that the PCR is set to input again, so there > is no time to shift the last data byte out to the RW-head > completely. Illogical, but that seems to be the case. Regarding the two BVC's were the discussion started with: the first one starts the proces of writing the last $55 and the second one makes sure it is written and not dumped like the databyte during the proces mentioned by Andre. I'm just wondering why the programmer cared so much for this $55 byte and neglected this databyte. Only one thing comes to my mind: two different programmers. One that likes to see things neatly closed and a sloppy one who knew that the 1541 didn't do anything with the last byte and so didn't care about it. It even can be a programming error but as it had no visible result, nobody noticed it. For Patryk: > LDA #$55 > LDX $45 > L784: > BVC L784 > CLV > STA $1C01 > DEX > BNE L784 Where do you initialise $45? Anyway, your routine also proofs the statement I made above. I also question the use of 'STA $1C01' here; it doesn't add anything. IMHO it could have been placed immediatly after 'LDA #$55'. BTW, the 1541 does the same. Why? -- ___ / __|__ / / |_/ Groetjes, Ruud \ \__|_\ \___| URL: Ruud.C64.org =====DISCLAIMER================================================================= De informatie in dit e-mailbericht is vertrouwelijk en uitsluitend bestemd voor de geadresseerde. Wanneer u dit bericht per abuis ontvangt, verzoeken wij u contact op te nemen met de afzender per kerende e-mail. Verder verzoeken wij u in dat geval dit e-mailbericht te vernietigen en de inhoud ervan aan niemand openbaar te maken. Wij aanvaarden geen aansprakelijkheid voor onjuiste, onvolledige dan wel ontijdige overbrenging van de inhoud van een verzonden e-mailbericht, noch voor daarbij overgebrachte virussen. The information contained in this e-mail is confidential and may be privileged. It may be read, copied and used only by the intended recipient. If you have received it in error, please contact the sender immediately by return e-mail; please delete in this case the e-mail and do not disclose its contents to any person. We don't accept liability for any errors, omissions, delays of receipt or viruses in the contents of this message which arise as a result of e-mail transmission. Message was sent through the cbm-hackers mailing list
Archive generated by hypermail pre-2.1.8.