I have an application where one Vision V130 PLC (Modbus master) reads over RS485 network 14 Jazz PLC –s (Modbus salves). Recently I add another 6 Jazz PLC-s to this RS485 network. The type of 14 old and four new PLC is JZ10-11T40 and other two new PLC –s are JZ20-R16. All Jazz PLC-s used MJ20-RS adapter. All termination resistors set up correctly (both ends ON, all others OFF). After all the installation and programming work was done, there are strange behavior with some new PLC –s.
Master PLC V130 can read all JZ10-11T40 type PLC-s but if it start reading JZ20-R16 type PLC –s then port settings of that PLC –s goes to default values and master can’t connect with them. Sometimes it happen immediately after restart (initializing correct port settings) and sometimes master can read slave during minute or two before
port settings changes their default values. Port settings I use: baud rate 9600, data bits 8, stop bits 2, parity no, HW flow control none, timeout 1s.
What can cause that kind of malfunction?