What's the problem of the RS485 communication?
I've designed a board with microcontroller (NXP, K64) to control i/o's. The uart port of the uC is connected to Maxim 3362 which converts the signal to #-Link-Snipped-# half duplex communication. Using modbus protocol in the uController, the communication flows towards the connector on the right in the scheme, from there to an outside rs-485 to USB dongle (which connects to a master PC).
![[IMG]](proxy.php?image=https%3A%2F%2Fi.stack.imgur.com%2FGY7OH.png&hash=489ee008a517edfcab40f0631e49e09f)
I'm experiencing communication problems and using a differential probe and oscilloscope to sample the Rx and Tx lines of the differential rs485 communication (at the board output connector, pins 4 and 5 in the drawing) I've seen the following picture:
![[IMG]](proxy.php?image=https%3A%2F%2Fi.stack.imgur.com%2FtGjKG.jpg&hash=9d46dcd89c279a7cca88edd881887d20)
![[IMG]](proxy.php?image=https%3A%2F%2Fi.stack.imgur.com%2FCrrG1.jpg&hash=51fbb1c8c6e285e9fb6b7cddd5c2c6e7)
The picture shows a message sent from the PC to the uController, before the uCOntroller answered - and answered wrongly (with RTS high, as expected).
As you can see inside the message sent there are one's and zero's. The zero logic has a lot of oscillating noise on it and the one logic seems quiet.
Furthermore, before the message starts the zero seems okay. This seems a bit strange because if the ground had noise on it I would have suspected that zero logic inside the message and the zero logic before the message starts would have noise (also '1' would have noise, I guess) and not the zero logic inside the message alone...
Furthermore, I had one time during all my experiments which it did worked as expected (it was working ok for few days until now), see the following:
![[IMG]](proxy.php?image=https%3A%2F%2Fi.stack.imgur.com%2FUz2h9.jpg&hash=4fff37498a2cd3c602d0cf7b1b209143)
As you can see in the second picture the '0' and the '1' seems okay and these pictures are from the same board.
is this a board problem, component problem?
I'm guessing it does not concern with the firmware... Any ideas?
I'm experiencing communication problems and using a differential probe and oscilloscope to sample the Rx and Tx lines of the differential rs485 communication (at the board output connector, pins 4 and 5 in the drawing) I've seen the following picture:
The picture shows a message sent from the PC to the uController, before the uCOntroller answered - and answered wrongly (with RTS high, as expected).
As you can see inside the message sent there are one's and zero's. The zero logic has a lot of oscillating noise on it and the one logic seems quiet.
Furthermore, before the message starts the zero seems okay. This seems a bit strange because if the ground had noise on it I would have suspected that zero logic inside the message and the zero logic before the message starts would have noise (also '1' would have noise, I guess) and not the zero logic inside the message alone...
Furthermore, I had one time during all my experiments which it did worked as expected (it was working ok for few days until now), see the following:
As you can see in the second picture the '0' and the '1' seems okay and these pictures are from the same board.
is this a board problem, component problem?
I'm guessing it does not concern with the firmware... Any ideas?
0
