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TCP/IP Ethernet Communications User’s Manual - August 1997 GFK-1084B
Establish Write Channel (2004)
The Establish Write Channel command requests that a channel be connected to a remote
PLC and that data from the local PLC be transferred (periodically) to the remote PLC.
The Command Block specifies the period, the number of writes to the server to perform,
and the timeout allowed in waiting for each transfer to complete. The first write is
performed immediately, regardless of the period specified.
Example 1 Command Block–Basic Example
Establish a write channel (channel 6) to a remote PLC at IP address 3.0.0.1. Return the
COMMREQ Status word to %R10. Write local PLC registers %R50-%R57 to remote PLC
registers %R100-%R107. Repeat the write indefinitely once every 7 seconds with a
timeout of 500 ms for each write.
Dec (Hex)
Word 1 00017 (0011) Length of Channel Command Data Block (17 - 25 words)
Word 2 00000 (0000) Always 0 (no-wait mode request)
Word 3 00008 (0008) Memory type of CRS word (%R)
Word 4 00009 (0009) CRS word address minus 1 (%R10) *
Word 5 00000 (0000) Reserved
Word 6 00000 (0000) Reserved
Word 7 02004 (07d4) Establish Write Channel Command number
Word 8 00006 (0006) Channel number (6)
Word 9 00000 (0000) Number of write repetitions (write indefinitely)
Word 10 00003 (0003) Time unit for write period (3=seconds)
Word 11 00007 (0007) Number of time units for write period (every 7 seconds)
Word 12 00050 (0032) Timeout for each write (500 ms)
Word 13 00008 (0008) Local PLC - Memory type from which to write data (%R)
Word 14 00050 (0032) Local PLC - Starting address from which to write data (%R50)
Word 15 00008 (0008) Remote PLC - Memory type at which to store data (%R)
Word 16 00100 (0064) Remote PLC - Starting address at which to store data (%R50)
Word 17 00008 (0008) Remote PLC - Number of memory units (8 registers)
Word 18 00001 (0001) Remote PLC - Network address type (IP address)
Word 19 00004 (0004) Remote PLC - Network address length in words (4)
Word 20 00003 (0003) Remote PLC - Register 1 of IP address (3)
Word 21 00000 (0000) Remote PLC - Register 2 of IP address (0)
Word 22 00000 (0000) Remote PLC - Register 3 of IP address (0)
Word 23 00001 (0001) Remote PLC - Register 4 of IP address (1)
Word 24 - 27 Remote PLC - Program Name (needed for access to remote %P
or %L) (zero terminated and padded)
Word 28 - 31 Remote PLC - Program Block (needed for access to remote %L)
(zero terminated and padded)
* Word 4 (CRS word address) is the only zero-based address in the Command Block.
Only this address requires subtracting 1 from the intended address.
(Word 7) Channel Command Number: Word 7 requests that a write channel be set up. If
the command is processed successfully, it will result in attempting the specified number
of transfers from the client to the server.
The term local PLC is
used here to identify the
client PLC-the PLC
that initiates the
communications
request.
The term remote PLC
is used here to identify
the server PLC -the
PLC that responds to
the request.