Just released version 0.2.3 of mbusd - open-source implementation of the Modbus TCP to Modbus RTU (RS-232/485) gateway.

Features:

• Small footprint - suitable to run on embedded devices and SBCs like Raspberry Pi
• Multi-master - multiple TCP masters can access slave devices in RTU network using same gateway
• Robustness - can retry requests with mismatched response CRC
• Flexible RTU modes - speed/parity/stop-bits/timeouts can be configured for RTU network
• Support for both of automatic and manual (using RTS bit) direction control types for RS-485 transceivers

Supported function codes:

• 01: Read coil status
• 02: Read input status
• 03: Read holding registers
• 04: Read input registers
• 05: Force single coil
• 06: Preset single register
• 07: Read exception status
• 15: Force multiple coils
• 16: Preset multiple registers

Project is distributed under the BSD license. Anyone interested in improving and extending mbusd code could fork project on GitHub. Pull requests are welcome. :)