Way, way, way back when I did use the 6551 (the original, not the current broken one), I decided I was going to use IRQs in both directions and plugged away at it until I had a “foolproof” driver.
I posted my first attempt at a driver along with my current schematic on the previous page, though I ...

The transmitter and receiver would gradually drift apart in timing and things would fall apart.
I'm not sure which transmitter/receiver pair you're referring to, but I assume you mean the Tx in U1 which is set to 8-N-2 and the Rx in the external PC that's set to 8-N-1? Doesn't that Rx simply see ...

I would still link RX and TX on one ACIA used for transmitting
Ah, right. I understand now. Thanks, George.

The attachments show where I am at the moment. None of this is tested yet and the code isn't complete so it isn't ready to assemble, but it should show where I'm aiming. I'm going to have ...

Thanks George. That's a much more comprehensive data sheet than the one currently available from WDC's site (dated August 21, 2021). I'll implement your suggestion, which means I'll have to revert to using the Rx part of U2 as the dummy and, no doubt, confuse myself in the process!

Thanks, Ed!

Some notes:
Thank you for taking the time to look and offer such helpful feedback. I'll tie DCDB and DSRB permanently low. CTSB too, for the time being. It would be nice to be able to use CTS/RTS eventually but that's some way away. I've noted your points about IRQB , removing the diodes and ...

I know your views on the subject, BDD, and respect them. I even posted my diagram in monochrome in your honour, having spent a long time reading before posting. To answer your question, I want to do it this way because I think it might work; because I haven't seen anyone else suggest it; because I ...

That's what I decided to do for my testing and it's shown that way in the diagram. It's much less confusing to think of one chip being dedicated to Tx and the other one to Rx.

- John

That's an interesting idea and I might just try it as I have a bunch in a tube otherwise unused...


Thanks Gordon. I should think a lot of members have a few of them lying around. This is the circuit I came up with and initial testing on a breadboard based on checking the status registers looks ...

Just a thought that occurred while reading about this hardware bug. I haven't seen it suggested by anyone else so apologies if it's there somewhere but I've missed it.

Since the Rx side of the W65C51 works as expected and can be used with interrupts, why not flog a dead horse back to life with ...