The F4 temperature controller communicates using RS-232 and is compatible with Modbus. It operates at a baud rate of 19200.

https://www.watlow.com/products/controllers/temperature-and-process-controllers/series-f4-process-controller

https://www.automationdirect.com/adc/overview/catalog/field_i-z-o/protos_x_i-z-o

https://www.cszindustrial.com/portals/1/pdf/WatlowF4_UserManual.pdf

![testrig](https://git.sdf.org/mharb/csharp-modbus-automation/raw/branch/dev/watlow-f4sd/ModbusWatlowRamp/F4TestRig.png)