Chapter 8. Communication Function
8-73
z It’s supposed that GM7U main unit is the master and it reads output coil data of the station no. 17, a
Modicon product.
z The master reads status of the input registers 30009 of the slave station no. 17. The input coil of the slave
station is supposed to be as follows and the data that are read is saved in any array variable RD_DW1 of the
2-sized WORD type.
Input Register 30009
Register status 16#000A
z Data is sent starting from the low bit by byte unit. An example of sending the above data is as follows.
Ex1) 00 0A
Function block input Input value
REQ Enter the input condition to operate
CH 16#1 or 1 Set channel (0, 1)
SLV_STNO 16#11 or 17 Slave station
FUNC 16#04 or 4 Enter ‘4’ when the output register is being read
SLV_ADDR 16#08 or 8
The start address to read from slave station
- Read the no. 8 to read starting from the output register 30009 in
accordance with the previous no. 8) “Modbus addressing rules.” And
the highest data of the data address doesn’t need to be input.
Because it’s automatically processed by the input value of the input
FUNC of the function block.
NUM 16#01 or 1
The total data size to read
- Example is to be read 30009, of which the total data size is 1. 1 is
16#0001 in hex, so input 16#01.
z Results
Variable Value to save
RD_DW1 [0] 16#000A or 10
RD_DW1 [1] X
z The variable to which saves the previously read data must be array type. The size of array type must be the
same or bigger than the size of the data of read. If it’s smaller, the error code is marked in STATUS.
z The previously read data is saved from the array variable, RD_DW1[0].
z The remnant part of an array variable is redundancy, after the variable is filled with the previously read data.
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