ProSoft Technology MVI69-MCM - Manual (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 D ATA )
is an array set to match the value entered in the
R EAD R EG C NT
parameter of the MCM1M
ODULE D EF
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 D ATA ) is an array set to match the value entered in the
W RITE R EG C NT
parameter of the MCM1M
ODULE D EF
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.