From: fachat (afachat_at_gmx.de)
Date: 2005-04-08 13:19:30
On Thu, Apr 07, 2005 at 08:09:29PM +0200, Patrycjusz R. Ćogiewa wrote: > Does anyone know what function has the PCR (mapped at $1C0C) of VIA2 > inside 1541? The PCR is the "Peripheral Control Register" of the VIA6521. It controls the behaviour of the hardware pins CA1, CA2, CB1 and CB2. Pleas see http://www.funet.fi/pub/cbm/documents/chipdata/ To see what the pins do, look at the schematics of the VC1541, at http://www.funet.fi/pub/cbm/schematics/drives/new/1541/tech for example in the file 1541-33b-right.gif. IIRC VIA2 is the drive controller VIA, so, the PCR controls the lines CB1 - not connected CB2 = MODE -> Output Enable (OE) of Gate Array CA1 = BYTE -> Gate Array Pin BYTE, also connected to S.O. of the 6502 CA2 = SOE -> Gate Array Pin SOE IIRC MODE determines whether data is written to or read from the drive head, BYTE is an input that determines whether the read or write of a byte is finished. And SOE I cannot remember. If you really want to know the exact meaning, you could analyze the drive schematics of the early (long board) VC1541 (e.g. in file 1541-35.gif under the abovementioned URL) where there was no Gate Array, but the logic was done in discrete logic (standard TTL chips). I did this once, but this is is something like editing sendmail.cf directly - you do it once and never again :-) AndrĂ© Message was sent through the cbm-hackers mailing list
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