12. Communication Design Examples M2 M3 Set the heating/cooling cycle time: 20s M1127 Set temperature control mode: cooling mode C0 counts once when data receiving is completed. Reset M1127 M1129 C0 counts once when communication timeout occurs Reset M1129 M1140 C0 counts once when data receiving error occurs Reset M1140 M1141 C0 counts once when parameter error occurs Reset M1141 Program Description: z Initialize PLC RS-485 communication port and set the communication format as MODBUS ASCII, 9600, 7, E, 1. The RS-485 communication format of TC should be the same with PLC.
z Since DTA series TC does not support the function code 10H (Write multiple words), the program needs 3 MODWR instructions to write 3 address data. z There are only 4 situations for MODBUS communication: flag M1127 for normal communication and M1129, M1140, M1141 for communication errors. Counter C0 counts once when any of the 4 flags is ON. Therefore, the program assures the communication reliability by monitoring the On/Off status of the 4 flags and performs 4 MODBUS z Once PLC starts running, the read/write actions for TC will be performed repeatedly instructions in order by the value in counter C0 according to [LD=] instructions.
DVP-PLC Application Examples 12-24 MODWR K1 H4712 K20 MODWR K1 H4718 K1 CNT C0 K10 RST M1127 CNT C0 K10 RST M1129 CNT C0 K10 RST M1140 CNT C0 K10 RST M1141