Is pin 19 of U23A going low, If not wrong switch settings.
Are you getting correct address signals to u19 pins 13,14
John
From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Thomas Owen
Sent: Monday, September 22, 2014 11:06 AM
To: n8vem...@googlegroups.com
Subject: [N8VEM-S100:5254] ZFDC Initial test questions - failing with possible timing issue?
All,
I have just completed assembly of the ZFDC and have begun the most basic tests outlined by in the build instructions:
"Go to your monitor and at 0H in RAM enter:
DB, 10, C3, 00, 00
Jump to 0H in RAM. This will have your Z80 continuously input from port 10H.
Check with a logic probe pin 12 of U19 pulses low". This was successful
"Then check that pin 1 of empty socket U16 pulses low". This was not successful.
So, I connected my logic analyzer to the chips in question and here I have what appears to be a timing issue:
What I see is that SINP goes HIGH, followed by PDBIN, which gives me the first low I need on the input of u20. The next signal, however, is from u19 pin 12 and is occurring at the wrong time altogether (needs to coincide with u21 out).
The result is that I do not ever see a low at pin 1 of u16 (u20 out in the above image).
System is a IMSAI chassis with standard front panel, Cromemco ZPU at 2 mhz, Interfacer 3, and Ram 17.
Any tips will be greatly appreciated!
Thomas
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