From: B. Degnan (billdeg_at_degnanco.com)
Date: 2006-10-19 14:57:28
I wonder if there is a way to hack/wire the top board to perform a pulse
"slap back" using an oscilloscope to locate the pulse and use that as a
trigger, kind of like a keyboard strobe? Excuse my limited grasp of your
project, I may be way off :-)
Bill D
At 09:40 AM 10/19/2006 +0200, you wrote:
>Hallo allemaal,
>
>
>I am busy with disassembling the controller part of the CBM 90x0. There is
>a piece of software, actually one line, of which I0m not sure if I
>understand it completely. But first some information:
>
>The 90x0 contains two boards and a MFM hard disk. The controller board
>drives the hard disk. The main board contains two 6502's, one for the IEEE
>communication and others things (as we are used to with the other IEEE
>drives) and the other 6502 for controlling on its turn the controller
>board. This is done using the SASI bus, the predesessor of SCSI.
>The 6522 involved is used controling the SASI bus.
>
>.eq PortB = $80 ; some control lines
>.eq PortA = $81 ; data
>.eq DDRB = $82
>.eq DDRA = $83
>.eq PCR = $8C ; CA1 = REQ (request, in)
> ; CA2 = ACK (acknowledge, out)
>All used signal are active (H).
>
>For transferring data from or to the controller board, the next four lines
>are the start of the used routines:
> lda PCR
> ora #$0A ; <====================
> and #$FB
> sta PCR ; reset ACK
>
>
>If I understand correctly, "ora #$0a" puts the 6522 in pulse mode. CA2 is
>(H) allt he time. But the moment Port A is written to or read from, a (L)
>pulse is sent towards the controller board. Is this correct?
>
>If this is the case indeed, I cannot use my 'off-the-shelf' solution, my
>self-built IEEE interface, as it lacks the means to detect that pulse. But
>replacing this board + HD with a PC wasn't meant as a permanent solution
>anyway, just as a starter to figure out how things exactly work.
>
>I looked at Andre's site and found out that the only difference between
>SASI and SCSI is that SCSI has an extra ATN line. So my first question for
>the SCSI experts amongst you: could it be so simple by replacing the board
>+ HD by a SCSI hard disk ??? But be aware, the condition is that there is
>no hardware change needed on the 6502 board. Later I want the drive to be
>able to handle bigger hard disks but I want to realize that by altering
>the ROMs and only as less as possible (I don't mind to be stuck to 16 MB).
>
>Another idea: replacing things with a micro controller + IDE-HD (or Flash
>card). Problems: what uC to use, how to program it? I myself am thinking
>of using an old 1541-II board as base. The advantage: I know 6502 ML and
>the onboard 6522 can handle the pulse problem for sure.
>
>Any input is welcome!
>
>
>--
> ___
> / __|__
> / / |_/ Groetjes, Ruud
> \ \__|_\
> \___| URL: Ruud.C64.org
>
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