Thanks, Chris. stty does indeed seem to help out with the serial settings.

Now, I've found out that my MAX485 chip is actually half duplex, and I didn't know that, but I guess I should have. The MAX488 chip is apparently full duplex, and I should have gotten that instead. So, I have to set a pair of pins to HIGH right before transmitting the command over RS-485, and then setting it to LOW immediately after, so that I can receive a response. HIGH is TX-mode and LOW is RX-mode

I ran out of time to get it working today, but I plan to make some more time during the next few days.

@Ken-Conrad Thanks!

I have now connected it up with 5V and put it on the RS485 line with minimalmodbus (python).

However, I can't get anything from the serial /dev/ttyS1. I read that the Omega 2 has set a default baud rate of 115200, but I can't figure out how to change it.

According to:

root@Omega-AAAA:/# dmesg|grep -i baud
[ 0.307914] 10000c00.uartlite: ttyS0 at MMIO 0x10000c00 (irq = 28, base_baud = 2500000) is a 16550A
[ 0.332361] 10000d00.uart1: ttyS1 at MMIO 0x10000d00 (irq = 29, base_baud = 2500000) is a 16550A
[ 0.341872] 10000e00.uart2: ttyS2 at MMIO 0x10000e00 (irq = 30, base_baud = 2500000) is a 16550A

it looks like the baud rate is 2500000? It seems to be 9600, after what stty tells me.

I need to use 19200 baud, no parity, for my modbus slave (Systemair HVAC). Will I have to change this in the boot parameters to the Linux kernel or can I change it after boot? How can I do it?

Update: I tried to set it using stty, and from what I can tell from stty it is now set correctly. But still no reply from modbus.

I could try to connect the 3.3V to the RS-485 board and see if it runs on it.

@Ken-Conrad It says on the MAX485 that operating power to the chip is 5V. The RS-485 voltages are higher, but it is designed to work with the Raspberry Pi UART, so I guess it should be compatible with the Omega 2.

I have this TTL UART to RS-485 board: https://www.aliexpress.com/item/5PCS-MAX485-RS-485-Module-TTL-to-RS-485-module-Raspberry-pi/32579369267.html

I have an Expansion Dock as well , but I can't find RX1 and TX1 there. (yes I can).

What do you mean by signal levels? I'm sorry, but I'm a bit new to this.

I can't figure out how to connect a MAX RS-485 chip to Omega 2 using the UART tx1 and rx1 pins when the Omega 2 is placed on the Mini Dock.

Is it pin 45 and 46? Will I get ac /dev/tty-something device in Linux?

Thanks for any pointing in the right directions!