#Schematic Review

1 messages · Page 1 of 1 (latest)

clever wren
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Hello everyone. I've been working on a project that combines a homebrew x86 PC project called the WeeCee with another called TinyLlama. it uses an ICOP SOM304RD-VI module for the processor and the rest of the board is essentially a carrier that has some components connected to the ISA bus, serial, USB, etc of the SOM.
I've put an ISA based device on-board called the PicoGus which is a sound card emulated with an RP2040 chip. I have been able to successfully use the PicoGus on the ISA bus of this SOM module on my dev board that I made but for some reason, it never gets detected by the SOM as it is on the carrier board. I'm wondering if someone who has some experience with similar projects can take a look at my schematic and see if I'm missing something. It's weird that it works fine connected over a traditional ISA slot but not directly connect through the carrier so I must have messed something up. Please see my schematic and let me know!

Screenshot_2025-01-15_at_8.48.47_AM.png
rotund seal
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C65 looks a bit weird.. It has no discharge resistor, so reset will probably only work once

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Also C54 loads U6C without a series resistor.. Smells not right.

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Lot of complex stuff there.. Will take too much time to go into details

clever wren
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interesting! let me take a look at that

clever wren
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ok I see. you're referring to the reset circuit for C65. the big question mark I've always had with stuff like that and this SOM is I'm not entirely sure what the SOM itself has onboard. it's possible it already has a cap and discharge resistor before the header but the reset has always worked properly. on other SOMs I've had to use discharge resistors but on this one, I'm not even sure if the debounce cap is required. I suppose I should experiment with that a bit.

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I have logic probes I could use but I'm kind of a noob still when it comes to ISA so I'm not entirely sure what I'm looking for either

rotund seal
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Reset pins are often made to pull hard to gnd.

clever wren
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if I were to put logic probes or even an osciloscope on the ISA bus for this device, what would I generally be looking for?

sly bolt