First post, by Predator99
I open a new thread as I think I need some assistance with my Lo-Tech ISA Rom-board...
ISA card with ROM at F000:0 ?
Unfortunately I didnt see I got an Rev.3
while ordering parts for the older one.
This is my board after assembling:
Problem: Regardless of the DIP setting, the ROM appears in a 32 kb window at E800:0 or also C800:0.... 🙁
I have the following differences to the Rev. 3 bill of materials that can potentially cause this issue:
1) SN74F521N instead 74HCT688N: are exactly the same, e.g. according to
"′ALS688 Are Identical to ′ALS521"
Therefore it should work?
2) 74LS33N missing:
Only needed for XT-slot-8
3) 7-pin instead of 8-pin resistor network:
The "empty" Pin 8 is connected to DIP-1 which switches the XT-slot-8 on and off. When the DIP is "off", there is no connection to anything else. Therefore this shoulnt be an issue?
4) Resistor network itself:
A "10k Bussed Resistor Network - Bournes 4608X-101-103LF" is required:
I checked with a spare of my 7-Pin:
- There is 10k between Pin1 and each of the other 6 Pins
- There is 20k between the other Pins, e.g. Pin 5 vs. Pin 6
--> this should be the correct one
5) I use the board with a SST-PH29EE010 instead of SST39SF010A. Both have same capacity and pinout. I am programming it in my TL866 and it can be read as SST39SF010A in the TL866. It is also read in the Lo-Tech board, but at the wrong adress as mentioned above. Theerfore this is also no problem?
Also re-checked all solder-points, seem to be OK.
I also assumed the SN74F521N is damaged. Unfortunately the 521/688 are not supported by the TL866 for Logic-IC test. I have in total 5 of the SN74F521N and also tested another one, but its the same...
Anybody have an idea where to start..?