Rockwell Automation 1771-SDN DeviceNet Scanner Module Installation Instructions - Manual (Page 30)

Publication 1771-IN014B-EN-P - September 2001
30 DeviceNet Scanner Module Catalog Number 1771-SDN/C
•
TXID (transaction ID) – when you create and download a
request to the scanner, the processor’s ladder logic program
assigns a TXID to the transaction. This is a one-byte integer in
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. The ladder logic program monitors rollover and
usage of TXID values.
•
size – the size of the transaction body in bytes. The transaction
body can be as many as 29 words (58 bytes) in length. If the size
exceeds 29 words, an error code will be returned.
•
port – the DeviceNet port where the transaction is routed. The
port can be zero (Channel 1) or one (Channel 2).
•
MAC ID (node address) – 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 attributes coupled
together identify the target slave device.
•
service – for each Explicit Message Request and Response, the
service attribute contains the service request and response codes
that match the corresponding request for the TXID.
service
port
TXID cmd/status
size
MAC ID
Transaction Body
(29 words)
word 0
word 1
word 2
Transaction
Header
(3 words)
word 31
15 0
One word = two bytes = 16 bits