ProSoft Technology MVI71-MCM - Manual (Page 25)

Installing and Configuring the Module MVI71-MCM ♦ PLC Platform
Modbus Communication Module
ProSoft Technology, Inc. Page 25 of 111
December 28, 2007
Data Transfer Parameter
The first five parameters of the configuration relate to the data transfer between
the module and the processor as follows:
ƒ
Write start register - Offset in the module's database where write data is
placed
ƒ Write register count - Number of registers to transfer from processor to
module
ƒ Read start register - Offset in the module's database where read data is
sourced
ƒ Read register count - Number of registers to transfer from the module to the
processor
ƒ Backplane fail - Number of successive transfer failures that cause
communication shutdown
ƒ Error Status Pointer - Offset in the module's database where the error
status is stored.
These parameters apply to both the side-connect and block transfer interfaces.
For the block transfer interface, the number of blocks to transfer between the
module and the processor is determined by the count values set in these
parameters. Each block can transfer a maximum of 60 words. For example, if the
Write Register Count parameter is set to 240, four write blocks will be transferred
(1 to 4) between the processor and the module. When the side-connect interface
is used, each block can transfer up to 1000 words of data. The user data files
must be set to match the values entered in this parameter set. For example, if the
Read Register Count parameter is set to 2100, three user data files must be
defined. The first two must contain 1000 elements and the last one must contain
at least 100 elements.
The Backplane Fail parameter determines if the module should continue
communicating on the Modbus network when the backplane transfer operation
fails. A value of zero indicates that the module should continue communicating
when the backplane is not operational. If the value is greater than 0, the
backplane will be retried the entered number of times before a failure will be
reported and communication will cease on the ports. When backplane
communication is restored, the module will resume communication on the
network. For example, if you enter a value of 10 for the parameter, the module
will stop all Modbus communications if 10 successive backplane errors are
recognized. When a successful transfer is recognized, the module resumes
communications.
The Error Status Pointer parameter defines the location in the module's database
where the error/status data will be stored. If the value is set to -1, the data will not
be stored in the user data area. A value between 0 and 4939 will cause the
module's program to store the data at the specified location.