ProSoft Technology MVI69-ADM - Manual (Page 39)

MVI-ADM ♦ 'C' Programmable Understanding the MVI-ADM API
'C' Programmable Application Development Module Developer's Guide
ProSoft Technology, Inc. Page 39 of 342
February 20, 2013
Block Request from the Processor to the Module
These blocks of data transfer information from the processor to the module. The
structure of the output image used to transfer this data is shown below:
Offset Description Length
0 Write Block ID 1
1 to n Write Data n
n=60, 120, or 240 depending on the Block Transfer Size parameter (refer to the configuration file).
The Write Block ID is an index value used to determine the location in the
module’s database where the data will be placed.
Block Response from the Module to the Processor
These blocks of data transfer information from the module to the CompactLogix
processor. The structure of the input image used to transfer this data is shown
below:
Offset Description Length
0 Read Block ID 1
1 Write Block ID 1
2 to (n+1) Read Data n
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 requests data from the
CompactLogix 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 network or operator
control through the module’s Configuration/Debug port.
The following example shows a typical backplane communication application.
If the backplane parameters are configured as follows:
Read Register Start: 0
Read Register Count: 480
Write Register Start: 480
Write Register Count: 480