Building a VersaTerm - A Retro Computing Serial Terminal

[PE1KEL]

I've also made this Versatherm. But I have a strange issue. If I connect RX and TX with a jumper, the Versatherm echoos my keys on the screen, so I suppose it works good.
If I connect a board, e.g. my Z80-retro-computer which works great on the ASCII VT100 video terminal of Geoff Graham, I don't see anything on my screen with the Versaterm-PCB.
I had the idea to invert the TTL-output and connect it to the RX of the Versaterm, and then I got some rubbish on the screen. Tried different baudrates, but no readable text when I pressed the reset button on the Z80-board.
No shortcircuits, no wrong resistors, diodes are okay, USB input works because I can go into the menu of the Versatherm.
Does anybody have an idea? I'm out of it at the moment.

[Editor]

Hi. It's hard to say without a closer look. I'm assuming you're just using the TTL serial connections, and have the voltage level switched to 5V (to match your likely Z80 ouput logic levels)?

Your external loopback was a good initial test. Do you have any other test equipment you can utilise? A scope would be very helpful here.

You shouldn't need to invert the output. You could test the non-transmission level easily with just a multimeter, to check you have the right signal polarity (but I'd say this is unlikely to be the problem).

The most common cause of serial issues, is either transposed Rx / Tx connection, baud-rate mismatch, or hardware handshake issues (but your external Rx <-> Tx link loopback test would seem to rule that one out).

[djrm]

Some terminals are fussy about the number of stop bits in use, this has caught me out once or twice. I always find it best to get comms working with a PC where it is easy to change setting and to then switch to a target system when you know things are working as expected. i.e. use a USB FTDI device to talk to the versaterm from a pc for starters. hth David.

[PE1KEL]

Thanks all for the reply.
I think there is something wrong with the level of the Z80 board, despite working on the other ascii terminal.
I connected the output from the Z80 board directly onto the 9pins serial port and Versaterm shows something more, so I have to look for something else with a TTL-output and I will see what happens then.
This will take some time but I will continue with the terminal till it works

[PE1KEL]

By the way: I have the Versaterm V1.2 PCB, while I noticed version 1.0 on github.
Does anybody know the difference between them? I've googled on the internet but I can't find anything about this.
Which PCB-version do you use?

[Editor]

By the way: I have the Versaterm V1.2 PCB, while I noticed version 1.0 on github.
Does anybody know the difference between them? I've googled on the internet but I can't find anything about this.
Which PCB-version do you use?

My VersaTerm PCB is also v1.2, as can be seen in my assembled PCB photo here (last photo): Building a VersaTerm – A Retro Computing Serial Terminal

I ordered my PCBs from the github published gerbers, so it must be all good.

[Editor]

I connected the output from the Z80 board directly onto the 9pins serial port and Versaterm shows something more, so I have to look for something else with a TTL-output and I will see what happens then.
This will take some time but I will continue with the terminal till it works

This suggests that your Z80 board has RS232 serial drivers.

If it's old-school, look for a MAX232 chip, or MC1488/MC1489 or SN75188/SN75189 RSR232 driver chips.

You definately don't want to connect RS232 levels to the TTL terminals. But you can use the 9-pin D connector instead, which carries the RS232 level serial interface.