MVI56E-MCM ♦ ControlLogix Platform Reference
Modbus Communication Module User Manual
ProSoft Technology, Inc. Page 127 of 209
Port 1 Current Error/Index
Port 2 Current Error/Index
The Read Block ID is an index value used to determine the location of where the
data will be placed in the ControlLogix processor controller tag array of module
read data. Each transfer can move up to 200 words (block offsets 2 to 201) of
data. In addition to moving user data, the block also contains status data for the
module. This last set of data is transferred with each new block of data and is
used for high-speed data movement.
The Write Block ID associated with the block requests data from the ControlLogix
processor. Under normal program operation, the module sequentially sends read
blocks and requests write blocks. For example, if the application uses three read
and two write blocks, the sequence will be as follows:
R1W1R2W2R3W1R1W2R2W1R3W2R1W1
This sequence will continue until interrupted by other write block numbers sent by
the controller or by a command request from a node on the Modbus network or
operator control through the module’s Configuration/Debug port.
Write Block
These blocks of data transfer information from the ControlLogix processor to the
module. The following table describes the structure of the output image.
Write Block from Processor to Module
The Write Block ID is an index value used to determine the location in the
module’s database where the data will be placed. Each transfer can move up to
200 words (block offsets 1 to 200) of data.
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