Panasonic AFP7CPS4E, Руководство пользователя

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MODBUS RTU
Master/Slave Communication
8-4
8.3 MODBUS RTU Master Communication (RECV)
8.3.1 Read Data from an External Device

Instructions
In master communication, PLC has the sending right, and executes communication by
sending commands to devices that support MODBUS-RTU, and receiving responses.
Messages in accordance with the protocol are automatically generated by PLC. In the user
program, reading and writing can be done simply by specifying the station no. and memory
address and executing SEND/RECV instructions.
External device
supporting Modbus-RTU
(Hex) 01 03 00 00 00 02 (CRC)
(Hex) 01 03 04 00 64 00 00 (CRC)
Command message
Response message
DT100 100
DT101 0
・・・・・・ ・・・・・・・・
・・・・・・ ・・・・・・・・
40001 100
40002 0
・・・・・・ ・・・・・・・・
・・・・・・ ・・・・・・・・
PLC
Specify and read station no. and address based on RECV instruction

Sample program

Send commands from the COM1 port of the CPU unit, read data from the data area of an external
device (station no. 1) 40001 - 40002, and write the content into PLC's data register DT100 - DT101.

Confirm that the unit is in the master mode (XC), and that the sending process is not in
progress for the same port (YC), and start up the SEND instruction.

In the UNITSEL instruction, specify the slot No. (U0) and the COM. port No. (U1).

In the RECV instruction, specify and execute the partner device station no. (U1), MODBUS
command and partner device station no. to be used (H0301), initial address (40001), No. of
data (U2), and initial address on the PLC side to save data (DT100). For the address of the
partner device, please check operating instructions, etc. of the relevant device.
R0
Master
communication
Clear to send flag
R100
UNITSEL U0 U1
RECV.US DT0 U2 DT100 H0301 H0
XC YC
Master
communication
Sending active flag
R100
Execute
RECV
Settings for communication port
S1: Slot 0 (U0)
S2: COM1 (U1)
Starting conditions for RECV
execution
Clear to send flag: ON
Sending active flag: OFF
RECV processing
S1: MODBUS code (H03) and
partner device station no. (H01)
S2: Partner device address (H0)
(corresponds to H0: 40001)
n: No. of data (U2)
D1: Data saving area (DT100)
D2: Execution result code (DT0)
（ ）
DF
S1 S2
S1 S2 n D1 D2
(Note 1) Operand [S1] of RECV instruction is specified by combining two hexadecimal digits of MODBUS function
code with two hexadecimal digits of partner device station no.
(Note 2) When the partner device is FP series PLC, Operand [S2] of RECV instruction can be specified using the
Device No.
(Note 3) The unit number and COM port number in the above program is applied when the COM.1 port of the CPU
unit is used.
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