ProSoft Technology ControlLogix MVI56E-SMGC User Manual page 72

MVI56E-SMGC ♦ ControlLogix™ Platform
Enhanced FMC722 TPU General Communication Module
5.2.1.4 Normal Data Transfer
Normal data transfer includes the transferring of data received by or to be transmitted
from the module and the status data. These data are transferred through read (input
image) and write (output image) blocks. Refer to Module Configuration for a description
of the data objects used with the blocks and the ladder logic required. The following
topics discuss the structure and function of each block.
Read Block
These blocks of data transfer information from the module to the ControlLogix processor.
The structure of the input image used to transfer this data is shown in the following table:
Word
Offset
0
Received 1
Data
2 to 52
Module 53 to 79
Status
80
81
The Block Sequence Number (word 81) is an index value used to signal to the
ControlLogix processor that a new block is ready for processing. The ladder logic must
recognize a change in this value and process the data encapsulated in the input image.
If data is available, a block containing the data received and the complete status data
area is passed to the processor. The value at word 0 in the block determines if data from
the client is present in the block. If word 0 is set to a value of –1, no data has been
received on the connected client that must be transferred to the processor. If word 0
contains a value of 0, the read block contains a single data block received by the client.
The following table lists the relationship between the values in word zero and their
meaning:
Value
-1
0
Word 1 of the input image determines the number of bytes in the data area of the block.
This word only has significance if word 0 of the block is set to zero. This word will have a
value less than or equal to 102, the maximum number of bytes that can be contained in
a single data block. The data set is located in the block starting at word offset 2. The
ladder logic must handle data received by the module. The structure of each block
received by the client is well defined in the SMGC protocol specification. If the client
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Description
Client Number for data received. If the word contains a value of -1, no
receive data is present. This version of the software supports a single
client. The module will only return of value of 0 when data is ready for
this client.
Number of characters (0 to 102) in the data block being passed to the
processor contained in the data area (2 to 52). In order to keep the
ladder logic processing simple, the module will only pass a single data
block to the processor in each transaction.
102 bytes of data area to hold the received data block.
This data area contains the status data block. Each block transferred
to the processor contains this set of information.
Number of characters processed from last write block or error code.
Block Sequence Number (Bumped each scan by module)
Description
No receive data in block
Client 0 data in block
Reference
User Manual
Page 72 of 98