ProSoft Technology MVI71-MCM - Manual (Page 61)

Reference MVI71-MCM ♦ PLC Platform
Modbus Communication Module
ProSoft Technology, Inc. Page 61 of 111
December 28, 2007
The configuration first creates four possible blocks for each Read and Write area
since every block contains 60 registers. Therefore, the Read and Write Block ID
generated would be:
Read Block ID Write Block ID
0 3
1 4
2 1
3 2
4 3
-1 4
0 1
1 2
2 3
If the ladder logic takes too much time to send a BTW instruction, the module
sends a new BTR instruction requesting the same Write Block ID.
The Read Block ID 0 is a null block to guarantee ladder logic consistency if the
user sets an empty Read Data area. The Read Block ID -1 transfers the
configuration data.
Read Data Area Application Examples
Ex. 1 : The following example shows a Read Data Area application; A Modbus
Master device sends a Modbus Write Command to an MVI71-MCM slave port.
The command destination address must be located inside the Read Data Region
(between 0 and 239).