Monday, November 7, 2016

RetroChallenge Epilogue and Apparent Success

After Review of my plan and schematics, I noticed a small error in the Eagle schematic I posted earlier.
  1. Pin 11 of the socket must be connected high (or to pin 12, or to a soft switch to enable video scanning on row E of RAM).
  2. Pin 11 of IC F2 must be disconnected and that line (not the IC pin) must be connected to ground instead (See my hand-drawn schematic).
I figured out problem 1 first. But when I booted I received half of a startup beep repeatedly, like it was stuck. It took a while until I realized I forgot Problem 2 since it was only on my older schematic. I used an IC socket and connected pin 11 and 12 and raised the IC leg. This is important as it decodes whether the Apple II is in RAM or I/O mode. The computer was stuck with no access to I/O or ROM (or simultaneous access to RAM and I/O or ROM).
F2 IC with pin 11 sticking out in a socket with pin 11, 12 connected It boots!

It seems to have worked! The computer shows the APPLE ][ greeting just as expected. I need to connect a keyboard and a disk controller card to test it all out and verify that all 48K is being accessed.

So, I now have an Apple II with 48K of 4164 DRAM in just one bank of RAM. Now for 64K. Or 128K...

2 banks of RAM installed for future 128K modifications

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