Prosoft-technology MVI69-MCM User Manual download pdf (Page 73)

MVI69-MCM ♦ CompactLogix or MicroLogix Platform Ladder Logic

Modbus Communication Module User Manual

ProSoft Technology, Inc. Page 73 of 167

March 22, 2011

3.2.2 User Data Objects

These objects hold data to be transferred between the processor and the MVI69-

MCM module. The user data is the read and write data transferred between the

processor and the module as "pages" of data up to 240 words long.

Name Data Type Description

ReadData INT[480] Data read from module

WriteData INT[480] Data written to module

The read data (R

EAD

ATA

)

is an array set to match the value entered in the

EAD

parameter of the MCM1M

ODULE

object. For ease of use, this

array should be dimensioned as an even increment of n words, where n = 60,

120 or 240 words. This data is paged up to n words at a time from the module to

the processor. The ReadData task places the data received into the proper

position in the read data array. Use this data for status and control in the ladder

logic of the processor.

The write data (W

RITE

ATA

)

is an array set to match the value entered in the

RITE

parameter of the MCM1M

ODULE

object. For ease of use, this

array should be dimensioned as even increments of n words. This data is paged

up to n words at a time from the processor to the module. The WriteData task

places the write data into the output image for transfer to the module. This data is

passed from the processor to the module for status and control information for

use in other nodes on the network. If this array is > 480 registers, change the

high LIM value in ReadData rung 1 and WriteData rung 21 of the ladder file.

3.2.3 Slave Polling Control and Status

Two arrays are allocated in the module’s primary object to hold the polling status

of each slave on the Master ports. This status data can be used to determine

which slaves are currently active on the port, are in communication error or have

their polling suspended and disabled. Ladder logic in the processor can be

written to monitor and control the status of each slave on a Master port. The

following table describes the structure of this object.

Name Data Type Description

SlaveStatus Decimal Slaves Status

Using special blocks, the processor can request the current data for the slaves.

Through the use of other blocks, the processor can enable or disable the polling

of selected slaves.

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