On December 12, 2020 at 16:07, Lyndel McGee said...
It could be a voltage level issue as RS232 specification was originally 12V and the Philips RFX is only 5 V.
The fact that the Arduino is having issues as well points me in this direction.
You might try a voltage level shifter. (search amazon) between the 2 ports and use +12V as a reference. You could also try using a MAX232 (again search amazon) and use +12V as input to that board.
I found this. Maybe it will help?
[Link: forum.allaboutcircuits.com]Thanks.
It kind of sounds like a voltage issue, but the other way around, since the TMA-1 can understand the RFX all right, but the other direction fails, and I'm reasonably certain that the VT420 is using providing proper +-13V signals. Looks like I have to re-assemble that Windows XP PC to get my parallel port oscilloscope running again.
The arduino RS-232 interface boards I'm using are based on the MAX232, and they should also output +-12V (or so), and if I read the datasheet correctly, they should accept 5V inputs, so I'd assume that the TMA-1 outputs something even more wonky.
