From: Baltissen, GJPAA (Ruud) (ruud.baltissen_at_abp.nl)
Date: 2005-04-22 09:43:01
Hallo Spiro, > Now, the format routine handles the same (writing a block to disk) a > little bit differently: > > .8:fd1e 50 FE BVC $FD1E ; make sure the last byte is written > .8:fd20 B8 CLV > .8:fd21 50 FE BVC $FD21 ; write another (!) byte to disk > .8:fd23 B8 CLV > .8:fd24 20 00 FE JSR $FE00 ; set read mode and data > port as input The actual formating of the track starts at $FCAE with writing 10240 times $55. This is more then enough to write the complete track. Then a loop starts at $FCB1. This loop handles writing a sector including its header. The loop itself goes as far as $FD1C. The last part of the loop is writing a number of $55's to the disk. This number depends on the number of tracks and is calculated at $FC17. Only after ALL sectors have been written, your part shows up by writing two extra $55's after the last $55's written by the loop. This bit of code isn't used anywhere else, certainly it is not used for writing a block to disk as you say. The only reason these $55 bytes are there is to give the drive time to switch from read- to write-mode (or vica versa) if needed, nothing else. So why these extra two bytes are written, I don't know; I don't see any advantage in doing so. I hope this helped :) -- ___ / __|__ / / |_/ 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
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