On Windows I use com0com, for Linux there is tty0tty that I haven't used yet. Instead of the sniffer, maybe you can use a null modem emulator, so that what you send from a (virtual) serial port will be received on another (virtual) serial port on your Mac, so that you can inspect the data sent/received. On Mac/Linux you should be able to use Wireshark to sniff USB communications, but I haven't done that yet personally. On Windows I use the one from HHD Software, it has serial, USB and TCP/IP sniffers. If pyModSlave works correctly on Mac, maybe try a software serial sniffer with your slave. I have no experience on Mac, but another option would be trying a Modbus Slave not written by you, for example pyModSlave and see if it works correctly on your Mac, it also shows you the packets sent/received. I work with ICP DAS tech support, and have used VirtualBox with tM-7561 and I-7561 USBtoRS485 converters, with both Linux and Windows hosts. Without more details, I would suggests another approach, if your final goal is to use the system in Linux: use a a virtual machine on Windows, with a Linux guest.

The Win PC variant is working so, hardware should be fine.

I'm already have no ideas what to check and how to make it work. Target PC (for slave) will be on Linux, so Mac is nearly closer than Win. Doesn't matter - correct request, but no response. When I'm trying this variant: Win PC (software slave) - USBtoRS485 - ICPCON tGW-715 (TCPtoRTU gateway) - Win PC (software master) everything works. Hardware: Mac (slave written by me) - USBtoRS485 - ICPCON tGW-715 (TCPtoRTU gateway) - Win PC (software master) Modbus RTU slave RS-485 failed to response - node.js I'm trying to write modbus slave and have one problem: I'm correctly receive requests from master, but when I try to response it's look like something is incorrectly sended to serialport, because when I plug RS485 sniffer - I see both req and res (in HEX).

Node js modbus rtu