Communication (RS232, RS485, I2C, SPI, UDP, TCP, ...)

Problems Sequential reading channels ADC MCP3424 via I2C

Jan Reitinger — Sat, 10 Jan 2026 14:49:00 GMT

Hi everyone,

@AlexanderH solved his MCP3424 multi-channel reading issue! Here's the key takeaway:

The Problem

When reading multiple channels sequentially from MCP3424, conversion time must be respected. Each configuration byte starts a new conversion:

12-bit: ~5ms (1/240 s) 18-bit: ~267ms (1/3.75 s)

Table 4.3 from MCP3424 datasheet lists all data rates by resolution.

The Solution

One-shot mode + proper timing between configure/read operations:

For 12-bit (2 channels):

// Channel 1 - configure + convert + read i2c_bufTx[0] = 0x80; // CH1, one-shot, 12-bit, gain x1 i2c_write_count = 1; i2c_read_count = 0; i2c_ret_fun = I2C(i2c_bus_handle, i2c_chip_address, i2c_bufTx, i2c_write_count, i2c_bufRx, i2c_read_count); Sleep(0.01); // wait for 10 ms before reading the first channel // Data rate: 12bit = 240 SPS, 14bit = 60 SPS, 16bit = 15 SPS, 18bit = 3.75 SPS i2c_write_count = 0; i2c_read_count = 3; i2c_ret_fun = I2C(i2c_bus_handle, i2c_chip_address, i2c_bufTx, i2c_write_count, i2c_bufRx, i2c_read_count); // i2c_bufRx[2] contains configuration byte channel1 = ((i2c_bufRx[0]<<8) + i2c_bufRx[1])/2; i2c_bufTx[0] = 0xA0; // channel 2, one-shot, 12bit, gain 1 (see MCP3424 datasheet) i2c_write_count = 1; i2c_read_count = 0; i2c_ret_fun = I2C(i2c_bus_handle, i2c_chip_address, i2c_bufTx, i2c_write_count, i2c_bufRx, i2c_read_count); Sleep(0.01); // wait for 10 ms before reading the second channel // Data rate: 12bit = 240 SPS, 14bit = 60 SPS, 16bit = 15 SPS, 18bit = 3.75 SPS i2c_write_count = 0; i2c_read_count = 3; i2c_ret_fun = I2C(i2c_bus_handle, i2c_chip_address, i2c_bufTx, i2c_write_count, i2c_bufRx, i2c_read_count); channel2 = ((i2c_bufRx[0]<<8) + i2c_bufRx[1])/2; Important Notes

Sleep time scales with resolution - 10ms works for 12-bit, 270ms needed for 18-bit

Original MCP3422 example worked because it read only 1 channel (no channel switching). The message from the previous tick was probably returned as a response.

Example Update

REXYGEN example library will be extended with:

read_mcp3424_12bit.c - 2 channels, 12-bit read_mcp3424_18bit.c - 2 channels, 18-bit

Big thanks to Alexander for the thorough debugging, testing different timing scenarios, and sharing his working scripts!

Cheers,
Jan

Problems reading from PCF8574A

Jan Reitinger — Mon, 18 Aug 2025 08:35:40 GMT

@AlexanderH Hi,
I'm sorry. For some reason I didn't get an email notifying me that you had replied. I'm glad you finally resolved the issue.

Cheers,
Jan

Bluetooth sensor with rexygen

cechurat — Tue, 08 Jul 2025 20:24:20 GMT

@har Hi Har,

I'm sorry, but we are not able to debug third-party Python code for you.

If you made it work under plain Python, then you can send the data to REXYGEN using the REST API. Have a look at "0302-03 REST API Python Bash etc", which sends data to REXYGEN using Python.

Kind regards,
Tomas

SPI comms for MCP41X

MikeyH — Sat, 28 Jun 2025 00:06:48 GMT

Hello All,

Is there, or does anyone have an example of using an MCP41X digital 257 position potentiometer with SPI?

Cheers,
Mike

Connection Problem

Jan Reitinger — Tue, 10 Jun 2025 15:17:53 GMT

Hi har,
Check if RexCore is running. I see that you are solving the Python code in another thread. It is possible that your code is not only causing the error, but also causing the entire RexCore to crash. Try connecting to the Raspberry via SSH and enter the command:

systemctl status rexcore

Cheers,
Jan

Modbus Tcp/IP communication Rpi(Rexygen)<->PC(Matlab)

Jan Reitinger — Wed, 26 Jun 2024 09:40:03 GMT

@stepan-ozana Thanks for sharing your solution! Unfortunately, I don't have the required toolboxes to run the script on my computer. However, the code is well-documented and well-organized, which should make it easy for anyone with the necessary Matlab toolboxes to use it without any issues.

'modbus' requires one of the following: Industrial Communication Toolbox MATLAB Coder Support Package for NVIDIA Jetson and NVIDIA DRIVE Platforms Error in example_ModbusTcpIP_Comm_RpiToPC (line 9) m = modbus('tcpip', IP_ADDR,MODBUS_PORT) %establish communication with the server (client)

Cheers,
Jan

REST API communication example

Jan Reitinger — Wed, 26 Jun 2024 06:34:25 GMT

@stepan-ozana
Thank you for confirmation. I will update the example. Unfortunately, quite large changes occur across Matlab versions, and there are situations where a script from older versions stops working in newer ones.

Cheers,
Jan

Raspbiian Bookworm

Jan Reitinger — Mon, 20 May 2024 16:33:35 GMT

@BailP Hello,
yes, there are REXYGEN packages (version 3) for Bookworm. Details are described here.

Cheers,
Jan

HW PWM on RPi?

Jan Reitinger — Thu, 23 Nov 2023 10:33:01 GMT

@stepan-ozana Hello, yes PWM flags should work as HW PWM on GPIO12, GPIO13, GPIO18, GPIO19 pins. The functionality should be the same as described here: https://www.raspberrypi.com/documentation/computers/raspberry-pi.html
https://www.electronicwings.com/raspberry-pi/raspberry-pi-pwm-generation-using-python-and-c

Best regards,
Jan

ASCII Commands Over RS485

Jan Reitinger — Tue, 01 Aug 2023 14:29:46 GMT

@georgedumitru I think the best documentation is this thread here on the forum. Byte array reading from communication is also discussed there.

Another helpful tool is definitely the example located at C:\Program Files\REX Controls\REXYGEN 2.50.12.14711\Examples\0203_Function_Blocks_REXLANG.

Communication with USBRLY82

cechurat — Thu, 13 Jul 2023 13:02:44 GMT

Hi George,

Thanks for your question. You need to create a kind of state machine which basically does the following (one line = one task period):

Write() - send a read request to the device Read() - save received data and length into a global buffer/variable and distinguish if the received message is complete Retry and repeat Read() if the previously received message was not complete

You will need to introduce a timeout - it can happen that you lost some data so there should be some timeout when you say "Message incomplete, resend the read request".

Cheers,
Tomas

REXduino and TSC2007

cechurat — Mon, 20 Feb 2023 19:13:33 GMT

@hrabalo Hi,

Thanks for getting back to us. I'm glad it works for you now.

Good luck with your project.

Cheers, Tomas

VSD single wire Modbus

MikeyH — Thu, 07 Jul 2022 01:39:45 GMT

Hi All,

I have a VSD I'd like to connect to the Monarco to control motor speed and read faults. Only it's a single wire half duplex. is there a way of connecting this to the Monarco?

VCC is 5-12vdc, so that's ok. I'm just not 100% of how I can connect it to the HAT. As it says, it's not RS485 compatible.

Cheers

Mike

eBUS

Jan Reitinger — Thu, 17 Mar 2022 14:38:10 GMT

@pancirm
Hello Michal,
as far as we know, no one implemented the eBUS in REXYGEN. However, implementation should be possible, for example, via eBUS <-> USB converter and REXLANG or Python programming block.

Cheers,
Jan

Can driver

reitinge — Wed, 16 Dec 2020 15:50:29 GMT

Hi Toni,
FilterIdMask can be used for filtering messages from more devices. In your case, there is only one device, so you can set FilterIdMask as 0xfff. For message decomposing, use the INTSM blocks (www.rexygen.com/doc/ENGLISH/MANUALS/BRef/INTSM.html). The basic example of using INTSM block can be found in this thread: https://forum.rexygen.com/topic/174/reading-and-writing-4-byte-floating-point-from-modbus?_=1609251284153
For decomposing a byte value into bits can be used block BDOCT(www.rexygen.com/doc/ENGLISH/MANUALS/BRef/BDOCT.html).

Cheers,
Jan

I2C EZO component

reitinge — Mon, 07 Dec 2020 14:08:59 GMT

@belgacom You are welcome 🙂

I2C with REXDuino

stepan.ozana — Fri, 16 Oct 2020 06:29:31 GMT

Me and my colleague finally implemented some functional solution. We make it public if anyone is interested. Many thanks to Ing. Tomáš Dočekal!
MCP4725_REXDuino_2_50_10.zip

SPI Communication / Rexlang / RelayPlate / DAQCPlate

cechurat — Thu, 06 Aug 2020 07:52:24 GMT

Hi Paul,

thanks for reaching out. You can now integrate Python scripts within REXYGEN 2.50.10 - for upgrade see post https://forum.rexygen.com/topic/120/installation-of-rexygen-2-50-10-testing

Python block documentaton: https://www.rexygen.com/doc/ENGLISH/MANUALS/BRef/PYTHON.html#x272-27100016

Let us know if it helped.

Regards,
Tomas

Best way to send commands over Ethernet to a 2Dcode (QRcode) reader

cechurat — Fri, 20 Mar 2020 15:38:43 GMT

Hi Ivan,

thank you for your question.
Using REXLANG function block you can manage Ethernet communication - see REXLANG documentation - part Communication functions: https://www.rexygen.com/doc/PDF/ENGLISH/BRef_ENG.pdf#page=447

Have a look also at "0504-01 Generic UDP Sender Receiver" example which can help you to start with the implementation.

Regards, Tomas

Connecting Racing Wheel to REXYGEN

jaroslav_sobota — Wed, 18 Sep 2019 08:33:02 GMT

Thanks for the explanation, now I understand. Nice solution.

Jaroslav

Telegraf (influxDB) integration

hubert — Thu, 29 Aug 2019 10:46:15 GMT

Hi @Scoobsalamander, thanks for info, I will look into it.

Hubert

Ethercat compatible?

Scoobsalamander — Mon, 05 Aug 2019 18:08:16 GMT

No problem, it is only for some hobby-related stuff so no rush.

Grtz,

Kris