12. Communication Design Examples M1129 C0 counts once when communication timeout occurs. Reset the flag M1129 M1140 C0 counts once when data receiving error occurs. Reset the flag M1140 M1141 C0 counts once when parameter error occurs. Reset the flag M1141 Program Description: z Initialize PLC RS-485 communication port and set the communication format as MODBUS RTU, 19200, 8, N, 2. The RS-485 communication format of AC motor drive should be the same with PLC. 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 3 MODBUS instructions in order by the value in counter C0. z When M0 = ON, [MODRD K1 H2102 K2] instruction will be executed. PLC will read the master frequency and output frequency of AC motor drive, store them in D1073~1076 in ASCII format, and automatically convert the content in D1073~1076 into hexadecimal values to D1050 and D1051. z When M1 = ON, [MODWR K1 H2000 D10] instruction will be executed. D10 = H22 and the drive will run in reverse. If D10 = H1, the drive will be stopped. z When M2 = ON, [MODWR K1 H2001 D2] instruction will be executed.
The frequency can be changed by the content in D2. z Once PLC starts running, the read/write actions for AC motor drive will be performed repeatedly according to [LD=] instructions. DVP-PLC Application Examples 12-10 CNT C0 K10 RST M1129 CNT C0 K10 RST M1140 CNT C0 K10 RST M1141