TTL-input doesn't show anything on screen with my Z80-retrocomputer

[Perdita-Olio]

Like I wrote in the title, nothing shows on screen when I connect my Z80-retrocomputer to the Versaterm.
Tried different settings, nothing helps.
The Z80-retro-PC works well on the ASCII VT100 video terminal Ver. 1.3 of Geoff Graham.
When I connect the RX and TX of the Versaterm the screen shows what I type in, so far so good.

I made an inverter between the TX from the Z80 and the RX of the Versaterm.
At that moment I get some rubbish on the screen, every time when I press the reset-button of the Z80-board the screen shows almost every time the same string of different figures.
Changing the settings will not help to make it readable. I know the baud-rate, the number of bits etc, the same settings as in the ASCII video terminal, but still no readable text.

I tried the latest firmware, I even took another RPico, looked for short-circuits, all the components on the right position and in the right way, especially the semi-conductors like the diodes.

I'm out of ideas. Can somebody give me a suggestion on what to look at?

[KyleCardoza]

I had this same issue until just now. I solved it by using a TTL-to-RS232 adapter, and plugging into the DE-9 port instead of TTL serial. Make sure to get one that has RTS/CTS inputs, if you're using ROMWBW.

[Cam-analogue]

I had the same issue with my SC131 Z80 CP/M machine. The SC131 can only sink about 0.6mA on Tx and can only pull down the RXIA interface to about 2.0V, not low enough to meet the Pico PI threshold for low of 1.8V. The solution is to replace the 1K R29 with 10K. The resistor change drops sink current needed from 2.6mA to 0.26mA, a value the SC131 can easily sink. I also changed R30 to reduce the sink requirement on the CTS.

[Perdita-Olio]

@ Cam-analogue.

Thanks for your reply. And I can say that was the solution to the problem, changing R29 and R30 into 10kOhm.
Some weeks ago, I had made a converter with a 74HC14, a Schmitt trigger with a wide voltage range and at least that worked, although it was not really stable.
Sometimes characters turned into just anything on the screen.
This week I have holiday and so wanted to try the modification with the resistors this weekend, because it just has to be possible.
And indeed: the best solution without extra parts, ánd stable.
Thank you very much for sharing your solution.

Best regards

[dhansel]

Thank you for your comments! I have updated the build instructions to mention that a 10k resistor for R29/R30 may be better in some cases.