ProSoft Technology MVI71-GSC - Manual (Page 51)

Reference MVI71-GSC ♦ PLC Platform
Generic Serial Communication Module
ProSoft Technology, Inc. Page 51 of 82
January 31, 2008
Word Offset Description
28 Number of characters (0 to 50) in Port 2 receive block (30 to 54). If the
receive data in the module is larger than 50 bytes, multiple blocks will
be transferred.
Any block with a value of -1 in this field represents the first or
continuation block and the block contains 50 bytes of data. The last
block of data will contain a positive number in this field that represents
the number of characters in the last block.
29 Number of characters transmitted (0 to 50) from last block write Port 2
Port 2
30 to 54 Port 2 data received (50-byte data area)
55 to 63 Reserved
The structure of the read data file when the side-connect interface is utilized is
shown below:
Word Offset Description
0 Block Sequence Number (Bumped each scan by module) (0 to 127)
1 Number of characters (0 to 400) in Port 1 receive block (3 to 202). If the
receive data in the module is larger than 400 bytes, multiple blocks will
be transferred. Any block with a value of -1 in this field represents the
first or continuation block and the block contains 400 bytes of data. The
last block of data will contain a positive number in this field that
represents the number of characters in the last block.
2 Number of characters transmitted (0 to 400) from last block write Port 1
Port 1
3 to 202 Port 1 data received(400-byte data area)
203 Number of characters (0 to 400) in Port 1 receive block (205 to 404). If
the receive data in the module is larger than 400 bytes, multiple blocks
will be transferred. Any block with a value of -1 in this field represents
the first or continuation block and the block contains 400 bytes of data.
The last block of data will contain a positive number in this field that
represents the number of characters in the last block.
204 Number of characters transmitted (0 to 400) from last block write Port 2
Port 2
205 to 404 Port 2 data received (400-byte data area)
405 to 499 Reserved
The Block Sequence Number (word 0) is an index value used to signal to the
PLC 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. The block contains the data received on each port and status data. The
length of data received on each port is contained in two words in each block
transferred from the module. The ladder logic handles all read data transferred
from the communication ports to the processor. The simple ladder logic
examples assume the received data block is less than or equal to maximum
number of words for the interface.
The receive buffer in the module is set to 4096 bytes. This large size permits the
buffering of a large amount of data before a transfer of the data to the controller
is required. The ladder logic to use a buffer larger than that provided by the
interface is more complex. The module buffers the data in this buffer until one of
the specified termination condition is recognized. The module will then transfer
the received block of data to the controller. If the block of data received is larger
than that for the interface, multiple blocks will be used to transfer the data to the
controller. The first block will contain a value of -1 in the Number of Characters