I’ve been using the reComputer R1000 for a while and I do see some use cases for it, but unfortunately my application requires modbus RUT over RS485 and I can’t make it work with software DE/nRE pin driving. The tcdrain() function takes a lot of time and when the driver switches to receiving mode the response was gone already (B19200 is not even that fast).
I think it is a bit shame having the designs not using the proper RTS pins for the UARTs of the CM4 module. The rs485 ICs are there but they are simple not usable… Unless, it is just to work in one direction or to connect to a custom made application where a delay can be added on the response.
Is it possible to have/see the design files so that I can try to cut some lines on the PCB and wire them directly to the rs485 DE/nRE pin?
From the CM4 datasheet I have:
GPIO17 - RTS1
GPIO3 - RTS2
GPIO7 - RTS3
GPIO11 - RTS4
GPIO15 - RTS5
UART 5,2 and 3 are the ones connected to the RS485 ICs, so I guess that I need GPIO15, GPIO3 and GPIO7. Is it possible to get access to that GPIOs in any location of the PCB?
Thank you,
Fernando Fontes
I have even considered to connect two of the drivers in parallel and use one just for transmission and the other just for reception. However, I need to connect to two devices, so, I would need 4 rs485 ICs…
Hi there,
So RS-485 has many configurations. Sounds to me like it is meant to be a HDX (half-Duplex)connection.
Master ? Slave or multidrop?
RTS/CTS for direction sending or receiving and does the driver require an ACK’ to turn the line around?
Lots to consider.
HTH
GL 
PJ 
you mean device tree or schematic?
Hi,
Thank you for replying.
Yes, I need it to be half-duplex. I need to send the command to read input registers and switch back to receiver mode to quickly receive the answer.
I agree that there are many RS-485 configurations, but I guess half-duplex is the most typical one.
Actually I just need RTS since the R1000 will be the master, so RTS is enough to drive the DE/nRE pin.
I meant the schematic, to see if there is a way to wire the RTS to the DE/nRE pin.
Thank you
Fernando
This is the schematic and PCB file of R1000: https://files.seeedstudio.com/wiki/reComputer-R1000/reComputer_R1000_schematic_design_files.zip. As you said, the current wiring of the DE pin of the 485 transceiver is unreasonable, which has caused us to spend a lot of energy on fixing this problem in software. There are still some problems though. We are already preparing for a hardware revision. We are deeply sorry for the inconvenience caused to you.
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Thank you for the reply @shuisheng_peng. We did our first pilot with two external USB-TO-RS485 converters. This solution is not ideal since only two USB ports are available on the R1000 and also because I’m adding extra hardware and not fully using the one that is on the R1000.
For now it was enough to validate the concept and we are now on a phase of designing the next steps and choosing a SBC to scale up. It would help our decision knowing if there is indeed the intention on doing an hardware revision and if so the estimated time for it to be ready. I would like to be able to order the main PCB to test it and take conclusion.
Best regards,
Fernando
