Casio PB-100 / Tandy PC-4 versions and documentation

[Jeff_Birt]

I was able to change the thread title on all of my postings. The broken PB-100 from eBay arrived and it is broken indeed. The little 2K nibble RAM chip is drawing 5ma and returning garbage to the processor.

The interesting part is that while it did not boot to the 'READY P0' screen the 'DEG' annunciator was on and the cursor was blinking. If I pulled the Phase 2 clock line (output of processor and only goes to RAM) the cursor no longer blinks! It seems that the routine that periodically blinks the cursor is the same one that periodically reads from the RAM. So, if the RAM does not return anything the cursor does not blink.

At least this unit can be used to test a 4-bit SRAM simulator