ProSoft Technology MVI71-GEC - Manual (Page 58)

Reference MVI71-GEC ♦ PLC 5 Platform
User Manual Generic ASCII Ethernet Communication Module
Page 58 of 86 ProSoft Technology, Inc.
May 11, 2011
Write Block
These blocks of data transfer information from the PLC processor to the module.
The structure of the BTW blocks used to transfer this data is shown in the
following table.
Word
Offset Description
0 Block Sequence Number (Read block number as set by module)
Transmit
Data
1 Server Number for data to transmit. If the word contains a value of -1, no
transmit data is present. If the word contains a value from 0 to maximum
number of servers -1, the block contains data to send to the specified
server in the module..
2 Number of characters to transmit to server. Each block can transmit up to
118 bytes of data. If this word contains a value of -1, the block contains 118
bytes of data and more blocks of data are to follow. When the module
received the last block containing a positive value representing the number
of bytes in the
block, the server will transmit the data to the client.
3 to 61 118 bytes of data to transmit on specified server.
62 Server Control Word
63 Module Control Word
In Word Offset 0 the Block Sequence Number is the value set by the module
received on the last read block transfer through the BTR on the module. The
ladder logic should copy this value from word 0 of the BTR image to word 0 of
BTW image in the ladder logic. This is the last operation performed when
constructing the write block. The module’s program will trigger the process write
block function when a new value is recognized in word 0 of the BTW image.
Word 1 of the block defines the server index that should receive the message. If
the word is set to a value of -1, there is no data in the message. A value of 0 to 4
will cause the enclosed message to be sent to the server if the message length is
set to a value other than zero and the server has an open connection. Word 2 of
the block defines the length of data in the block. Up to 118 bytes of data can be
sent in each block starting at word offset 3 in the block. If the message to be sent
to a server is longer than 118 bytes, multiple blocks are required. As long as
more than 118 bytes are required to send, the message length field should be set
to a value of -1 and 118 bytes of data should be placed in the block. When 118 or
fewer bytes remain to be sent, the message length field should be set to that
value and the remaining data placed in the block. The server will accept
messages up to a length of 8192 bytes. If a message longer than 8192 bytes is
sent to a server, a transmit overflow error will be recorded and the message will
be sent when 8192 bytes are received. The remaining part of the message will
be sent as it is received.