RevPi Core S - Problems reading USB port Serial data

[Victor.Olofsson]

Hi,

I have been trying to connect a RevPI Core S to a machine that data over rs232 to catch this data i want to connect the machine using a rs232 to usb and then by using Python & pyserial read and process the data. I have verified that /dev/ttyUSB0 exists and i have configured pyserial with the same settings as the machine (baud rate, parity etc.)

However this is where im having problems im not getting any data in /dev/ttyUSB0 and im having trouble figuring out what to do or if i have missed anything.

Hardware:
RevPI Core s
1P3FFCB-USB-SERIAL (Serial to usb converter)
Mystery machine that sends data over serial

Thanks in advance for any help,
// Victor

[dirk]

Hey Victor, I have created a test setup and hope it shows how easy you can transfer serial data:

1. Start miniterm

Code: Select all

python3 -m serial.tools.miniterm /dev/ttyUSB0

2. Set local echo on

Code: Select all

[STRG] + T, [STRG] + E

3. Monitor Pin 2 of D-SUB-9 plug - Pin 5 is GND

USB-RS232 RS Sniff Pins

4. Type something into miniterm

Here is the result:

I have also used a USB-FTDI converter so it is the same driver as you use, I think.

FTDI USB-RS232 driver

I must admit that I used a beta RevPi Bookworm OS image on my device:

Code: Select all

pi@RevPi39627:~$ uname -a
Linux RevPi39627 6.6.0-revpi2-rpi-v8 #1+deb12+1 SMP PREEMPT_RT Thu Aug 29 07:50:23 UTC 2024 aarch64 GNU/Linux

Some ideas for your troubleshooting:

• Use an oscilloscope or a logic analyzer to monitor the data lines
• How about the edges of the rectangle signals?
• How about echoes?
• Maybe you need to use terminating resistors - yes I did not use them, but this was just a quick test with short cables

Typical signal without terminating resistors

[Victor.Olofsson]

Hi,

Thank you very much for the detailed reply, we where able to perform a loopback test and identify that the serial convert cable works. The problem in the end was that the hardware we communicated with did not seem to have the standarized rs232 pin order. The problem is now solved and we can read data without any problems

// Victor