Allen-Bradley, Siemens, Omron, Delta, Mitsubishi ladder logic, ST, structured text, Modbus/PN.
We are commissioning a S7-1200 (CPU 1214C DC/DC/DC) with a CB 1241 RS485 communication board connecting to 4 energy meters over Modbus RTU. Randomly, `MB_MASTER` throws error code `8281` (Module negative acknowledgement / Timeout). Baud rate is 9600, 8-E-1. 120 ohm termination resistors are installed on both ends. What could cause intermittent 8281 timeouts on CB 1241?