ProSoft Technology MVI94-MCM-MHI - Manual (Page 78)

Reference MVI94-MCM ♦ Flex I/O Platform
User Manual Serial Communications Modbus Communication Module
Page 78 of 109 ProSoft Technology, Inc.
March 29, 2011
Data is transferred between the processor and the module using the block
identification codes of 1 to 666 and 9956 to 9958 and 9960. The other block
codes control the module from the processors ladder logic. They are
implemented when the ladder logic needs to control the module. In order to use
one of the blocks, the ladder logic inserts the data and code in the output image
of the module. The data should be set before the code is placed in the block.
This operation should be performed after the receipt of a new write block from
the module. A discussion of each set of codes is given in the following topics.
Event Blocks (1000 to 1255)
These control blocks are sent from the processor to the module to execute a
Modbus command out the Modbus master port. It should be used for commands
that are not found in the command list. Use blocks 1000 to 1255 to execute
commands in the list under processor control. The format for this block is shown
in the following table.
Block Request from Processor to Module
Word Offset Description
0 This word contains the slave device address on the Modbus network to be
considered with the command. This value is added (0 to 255) to the value of 1000.
This generates a block identification code of 1000 to 1255.
1 This word contains the internal Modbus address in the module for the command.
2 This word contains the count parameter that determines the number of digital
points or registers to associate with the command.
3 The parameter specifies the swap type for the data. This function is only valid for
function code 3, 6, and 16.
4 This word contains the Modbus function code for the command.
5 This word contains the Modbus address in the slave device to be associated with
the command.
6 Reserved
The data contained in the block is used by the module to construct a valid
Modbus command and defines what data in the virtual Modbus database to use
with the command. These parameters are the same as defined for the command
list. Refer to the Commands section of the documentation for more information.
When the module receives a block 1000 to 1255, it will check the command
queue for an available position. If there is space in the command queue, the
module will construct a command and place it in the queue. The module will
respond with the following block in the input image after processing request.