Read Block - ProSoft Technology MVI69-DFCM User Manual

Functional Overview

2.2.1 Read Block

These blocks of data are used to transfer information from the module to the
CompactLogix processor. The structure of the input image used to transfer this data is
shown below:
Offset
2 to (n+1) Read Data
where
n = 60, 120, or 240 depending on the Block Transfer Size parameter (refer to the
configuration file).
The Read Block ID is an index value used to determine the location of where the data will
be placed in the CompactLogix processor controller tag array of module read data. The
number of data words per transfer depends on the configured Block Transfer Size
parameter in the configuration file (possible values are 60, 120, or 240).
The Write Block ID associated with the block is used to request data from the
CompactLogix processor. Under normal, program operation, the module sequentially
sends read blocks and requests write blocks. For example, if three read and two write
blocks are used with the application, 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 DF1 network or operator control
through the module's Configuration/Debug port.
The following example shows a typical backplane communication application.
Assume that the backplane parameters are configured as follows:
Read Register Start:
Read Register Count:
Write Register Start:
Write Register Count:
The backplane communication would be configured as follows:
6
Description
0 Read Block ID
1 Write Block ID
0
480
480
480
Length
1
1
n
ProSoft Technology, Inc.
MVI69-DFCM User Manual
June 24, 2004