Using DeviceNet Explicit Messages 6-5
Each of the data fields in the transaction header are one byte in length:
Data Field Description
TXID Transaction ID — when the processor creates and downloads a request to the scanner, the
processor’s ladder logic program assigns a TXID to the transaction. This is a one-byte integer
in word 31 the range of 1 to 255. The scanner uses this value to track the transaction to
completion, and returns the value with the response that matches the request downloaded by
the processor.
COMMAND For each download, a command code instructs the scanner how to administer the request:
0 = Ignore transaction block (block empty)
1 = Execute this transaction block
2 = Get status of transaction TXID
3 = Reset all client/server transactions
4 = Delete this transaction block
5-255 = Reserved
STATUS For each upload, the status code provides the processor with status on the device and its
response:
0 = Ignore transaction block (block empty)
1 = Transaction completed successfully
2 = Transaction in progress (not ready)
3 = Error — Slave not in scan list
4 = Error — Slave off-line
5 = Error — DeviceNet port disabled or off-line
6 = Error — Transaction TXID unknown
7 = Unused
8 = Error — Invalid command code
9 = Error — Scanner out of buffers
10 = Error — Other client/server transaction in progress
11 = Error — Could not connect to slave device
12 = Error — Response data too large for block
13 = Error — Invalid port
14 = Error — Invalid size specified
15 = Error — Connection busy
16-255 = Reserved
PORT The DeviceNet port used by this message. The port must be zero (Channel A) on a
1747-SDN scanner.
SIZE The size of the transaction body in bytes. The transaction body can be up to 29 words
(58 bytes) in length. If the size exceeds 29 words, an error code will be returned.
SERVICE The service attribute contains the DeviceNet service request and response codes that match
the corresponding request for the TXID.
MAC ID The DeviceNet network address of the slave device where the transaction is sent. This value
can range from 0 to 63. The port and MAC ID uniquely identify the target slave device. The
slave device must be listed in the scanner module’s scan list and be on-line for the Explicit
Message transaction to be completed.
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