I've posted below the 512K expansion connector (E3) from the original 128K logic board as drawn in the Bowmarc schematics.
H3NRY, I'm just curious why your MacDraw schematics don't also show this insertion point. Aren't the original 128K & 512K boards virtually identical except for the incorporation of the additional multiplexing circuitry?
The Bomarc schematics are inclusive of all three logic board models, the 820-0086-C, 820-0068-F and the 820-0141-A. However, they do not really show how the multiplexing circuitry is incorporated into the E3 access. In trying to map these to your schematics, I was able to map the CPU access (A18 & A17) from holes 3 & 6 respectively, pin 1 of the RAM array to hole 2, and hole 5 & 4 to pins 2 & 14 on your 512K circuitry. The one pin I can't reconcile is 3 & 4 on your schematic, as I am out of holes on the E3. It's also interesting to note that hole 1 at E3 must be severed from 2, just like the connection at W1.
Also, before I go any further with this little project, is this unfilled triangular symbol (△) supposed to be a ground or a pullup? Both yours and the Bowmarc seem to have both this and a traditional ground symbol used interchangeably. More confusing is that you show resistors and capacitors in the 512K expansion circuitry yet, you show very few resistors and capacitors elsewhere in the schematic, while the Bowmarc is a bit more thorough. Love to learn more about how they came about.
H3NRY, I'm just curious why your MacDraw schematics don't also show this insertion point. Aren't the original 128K & 512K boards virtually identical except for the incorporation of the additional multiplexing circuitry?
The Bomarc schematics are inclusive of all three logic board models, the 820-0086-C, 820-0068-F and the 820-0141-A. However, they do not really show how the multiplexing circuitry is incorporated into the E3 access. In trying to map these to your schematics, I was able to map the CPU access (A18 & A17) from holes 3 & 6 respectively, pin 1 of the RAM array to hole 2, and hole 5 & 4 to pins 2 & 14 on your 512K circuitry. The one pin I can't reconcile is 3 & 4 on your schematic, as I am out of holes on the E3. It's also interesting to note that hole 1 at E3 must be severed from 2, just like the connection at W1.
Also, before I go any further with this little project, is this unfilled triangular symbol (△) supposed to be a ground or a pullup? Both yours and the Bowmarc seem to have both this and a traditional ground symbol used interchangeably. More confusing is that you show resistors and capacitors in the 512K expansion circuitry yet, you show very few resistors and capacitors elsewhere in the schematic, while the Bowmarc is a bit more thorough. Love to learn more about how they came about.