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Goals and Symptoms
Xxmit Error code 120 - could not set PLC UART
Causes and Fixes
The most common cause of XMIT / XXMIT error 120 "XXMIT Could Not Set PLC UART" is trying to access a Modbus port that doesn't exist. Since you have a TSX Momentum 171CCC78010 which has 2 Modbus ports, the second most common cause of error 120 "XXMIT Could Not Set PLC UART", it trying to set 2 Stop Bits in a TSX Momentum. The UART that's used for the TSX Momentum Modbus port is not capable of 2 Stop Bits (only 1).