Reply 20 of 23, by Susanin79
Here is the some positive update for this project 😀
Finally I was able to run it with the 4 SIMM modules, both Toshiba and Siemens works well. But... It can not run both DIP and SIMM at the same time, it is a pity, I'm afraid that it unable to support more than 4 meg at once. So sad, this MB shows optimal performance for 386-33 cpu, see results attached.
I have played a bit with SW 2 and found:
Switch 5 from SW2 do the selection of memory type
So here is the SW2 config for SIMM
1 1 1 1 1 1 0 0 boot as 640K
1 1 1 0 1 1 0 0 boot as 1664K
1 1 0 1 1 1 0 0 boot as 2688K
1 1 0 0 1 1 0 0 boot as 3712K
I have tried to trace the SIMM pins, and found that most address lines except A10 and A11 goes to U95 and U94 IC chips marked as "74F244PC" (A0-U95_18, A1-U95_16, A2-U95_14, A3-U95_12, A4-U95_09, A5-U95_07, A6-U95_05, A7-U95_03, A8-U94_14, A9-U94_12). Address lines from DIP connected to U93 and U94, was able to trace 10 lines. Not finished with the expansion memory slot, just found that Data lines from SIMM may be found within the slot pins.
As for the jumpers, did not dig deep, but it looks like jumper W6 has connected to 16MHz oscillator, W5 connected to IC U68 marked as "DM74LS175N"
Will continue with tracing and post updates.