Re: 1551 Repair - 28 pin 6523 Wanted

From: Gerrit Heitsch <*gerrit_at_laosinh.s.bawue.de*> Date: Sat, 08 Mar 2014 18:42:00 +0100 Message-ID: <531B5668.7020401@laosinh.s.bawue.de> · gerrit_at_laosinh.s.bawue.de

On 03/07/2014 09:55 AM, John McKenna wrote:
> Excellent, thank you.  That makes a lot more sense. I'll see if I can
> make it fit a 64/32.

Here's something else I remembered today.

All the 1551 I have seen use a 6525A as the TIA, but I remember seeing 
an Image of a 1551 PCB that used a 6523A. Looking at the schematics of 
the drive (*) confirms that the drive does not use the IRQ capability of 
the 6525, the only IRQ source in a 1551 is a 555 rigged as an oscillator 
and hooked up to _IRQ of the 6510T. The code seems to be doing 
everything else by polling (in or out of the IRQ routine).

(*) http://zimmers.net/anonftp/pub/cbm/schematics/drives/new/1551/251860.gif

So, to me it looks like what needs to be implemented to keep our 1551 
running is an CPLD implementation of the 6523 which is a bit simpler 
than the 6525.

Also, the Gate array used in the 1551 should be the same as was used in 
the 1541-II and 1570/1571.

I can't read it, but it looks interesting:

  http://hup.hu/node/130935

  Gerrit

       Message was sent through the cbm-hackers mailing list