ProSoft Technology MVI56E-MCM/MCMXT - Manual (Page 121)

MVI56E-MCM ♦ ControlLogix Platform Reference
Modbus Communication Module User Manual
ProSoft Technology, Inc. Page 121 of 199
June 18, 2014
Word Offset Description Length
209 to 210 Run Number 2
211 to 217 Port 1 Error Status 7
218 to 224 Port 2 Error Status 7
225 to 230 Data Transfer Status 6
231 Port 1 Current Error/Index 1
232 Port 1 Last Error/Index 1
233 Port 2 Current Error/Index 1
234 Port 2 Last Error/Index 1
235 to 248 Spare 14
249 Read Block ID 1
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:
R1W1  R2W2  R3W1  R1W2  R2W1  R3W2  R1W1 
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
Word Offset Description Length
0 Write Block ID: -1 to 50 1
1 to 200 Write Data 200
201 to 247 Spare 47
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.