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Re: Saturn 128k Problems

On Tue, 5 Jun 2012, Steven Hirsch wrote:


On 06/05/2012 07:57 AM, Michael Black wrote:

On Tue, 5 Jun 2012, Steven Hirsch wrote:


On 06/04/2012 10:49 AM, Hugh Hood wrote:

Steve:

I booted up RoboCAD on my IIe this morning and tested:
A. Ctrl-Reset -> RoboCAD 'traps' the reset key and presents a message about 
'Press Return to Continue'

This keeps you from losing your drawing and keeps (most) folks out of the
monitor for disassembly

B. OA-Ctrl-Reset -> the machine reboots
This is in a machine with a Transwarp (with the Saturn card selection), so 
throw that variable into my test results.
I cannot reproduce that, leading me to believe that I do have a problem with 
the Saturn board.  I'm going to try swapping out some of the LS TTL logic
for newer parts and see if I can get it to behave.

Would still be great if someone had the schematic.



I recall that it used that pair of Motorola ICs designed for controlling
dynamic ram, one is a multiplexer the other is a controller. Large multipin ICs, and they should jump out when you look at the board. There should be a 
datasheet or application note devoted to those ICs, and I suspect the board
can't be much different from that "typical design". That would make a good
start to a schematic, the interface to the bus can't be too complicated.
Actually, only a single large-package part: MC3242AP. But, that's a good suggestion. I'll see if I can chase up any data sheets.
That's definitely one of the two numbers I'd have expected there. It's been too long to remember which of the two it is, the multiplexer or the controller.
Wait, a websearch says it's the multiplexer so it will provide less information than if it was the controller or both. It just does the work of 74LS157s or whatever the Apple II uses to multiplex to the address lines of the dynamic ram. Since the card has to do a lot of work without the controller, this is less of a start than I'd hoped.
I remember tracing the power supply in the original Macintosh, sort of a complete schematic but very messy. And then suddenly I realize it looks a lot like the Apple II power supply, so I dig out the Apple II manual and yes, the schematic is more ore less the same. With the Apple II power supply schematic, I then went and recopied what I'd traced in the same layout, and that worked out the bits I hadn't got.
Which made me realize that sometimes you can make a guess, and then test the circuitry to see if it matches the guess. 

  Michael