HP41CX "PRA" Misbehaving on TULIP

[ThomasF]

(10-30-2024 01:16 PM)rocket.scientist Wrote:  I did find U5 behaved oddly when I put a scope on it. It wasn't "not" working, but still odd. For now I have JP2 pulled and U5 pin 3 lifted. Per the schematic this takes the U5 logic out of the picture. I have ordered replacements.

I can't see where monitoring FI is critical to the TULIP HPIL function, but I'll ask to be sure. Is FI monitoring important here?

No, the U5 is "only" used to let the Pico read back the FI line (used for tracing), it is not used to drive or interfere with the 41 bus in any way, only to read the state if another device - apart from Tulip - should drive the line.
If (and only if) the U5 is broken and somehow interfere with the bus then the behavior is unpredictable.

I.e. you should be able to use the Tulip board without the U5 even mounted and only loose the ability to trace the FI line - but no other feature or functionality should be affected.

With that said, the HPIL uses the FI line to flag it's state to the 41, so if FI fails somehow, then the HPIL will most probably fail as well.

At least AFAIK ...

Cheers,
Thomas