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GFK-1084B Chapter 3 Programming Communications Requests
Establish Read Channel (2003)
The Establish Read Channel Command requests that a channel be associated with a
remote PLC and that data from the remote PLC be transferred (periodically) to the local
PLC. The Command Block specifies the period, the number of reads from the remote to
perform, and the timeout allowed in waiting for each transfer to complete. The first
read is performed immediately, regardless of the period specified.
Example 1 Command Block–Basic Example
Establish a channel (channel 5) to a remote PLC at IP address 3.0.0.1. Return the
COMMREQ Status word to %R10. Read remote PLC registers %R50-%R57 to local PLC
registers %R100-%R107. Repeat the read 10 times once every 7 seconds with a timeout
of 500 ms for each read.
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 02003 (07d3) Establish Read Channel Command number
Word 8 00005 (0005) Channel number (5)
Word 9 00010 (000A) Number of read repetitions (read 10 times)
Word 10 00003 (0003) Time unit for read period (3=seconds)
Word 11 00007 (0007) Number of time units for read period (every 7 seconds)
Word 12 00050 (0032) Timeout for each read (500 ms)
Word 13 00008 (0008) Local PLC - Memory type at which to store data (%R)
Word 14 00100 (0064) Local PLC - Starting address at which to store data (%R100)
Word 15 00008 (0008) Remote PLC - Memory type from which to read data (%R)
Word 16 00050 (0032) Remote PLC - Starting address from which to read 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 read channel be set up. If
the command is processed successfully, it will result in attempting the specified number
of transfers from the server to the client.
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.