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 listReceived on 2014-03-08 18:00:07
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