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Homebrew TVT I picked up

Can anyone sort of explain to me how a typical serial i/o works with a UART like the AY-1013 ? I'm trying to track down the problem with this machine. It seems to receive - although it is getting the incorrect characters (like it gets a weird character instead of the $ prompt for SWTBUG). So I have two working theories - one is that the transmit part of the circuit just isn't working, the other is that there's some kind of memory fault and when I type it's trying to transmit the wrong characters and the computer just is ignoring it.

What I can see when I type are the bits being set up on DB1-DB8, and they stay that way until the next keypress. I am not seeing a strobe. I've got an MC1488 and an MC1489.. I assume the MC1488 is on the transmit side so that'll be the next thing I check out tonight.
 
Question: what purpose would there be to put an EPROM in a machine where there's no processor?

I just dumped all three EPROMs in this thing. One has absolutely nothing in it.. it's all 00s, the others have code like below. I'm wondering if the code just happened to be there, and these 1702As are just being used for some other purpose.

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Question: what purpose would there be to put an EPROM in a machine where there's no processor?

Tons of reasons. An EPROM can be used generically to translate any arbitrary input into any arbitrary output, so you can use them as address decoders, data translators, keyboard encoders, or as “microcode” for more complex state machines, the sky’s the limit.
 
Thank you!

And as I say that, I happened to turn over one of the EPROMs in question, and it has a little label that says 'TVT Functions'. So I'm guessing this EPROM could be the controller for functions like clearing the screen. I really wish I understood how that would work.. ie how hitting a CTRL sequence would trigger something in the EPROM and then cause something to happen.
 
Yeah I didn't post the whole thing.

Here is a complete dump of FE00-FEFF. Would love to figure out how it works.

I'm trying to document the connections between boards. The board I think that is giving me trouble is a perfboard with an edge connector. It has 3 74193s and some other support chips. If I press down on the back side of it, I start getting correct feedback from the computer, but if I give SWTBUG the Clear screen command.. it goes crazy until I release. Then if I release I get a cursor.. and I can type stuff and the cursor moves.. but nothing appears onscreen.
 

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