Rockwell Automation 1771-SDN DeviceNet Scanner Module Installation Instructions - Manual (Page 28)

Publication 1771-IN014B-EN-P - September 2001
28 DeviceNet Scanner Module Catalog Number 1771-SDN/C
2. The scanner module transmits the Explicit Message Request to
the slave device over the DeviceNet network.
3. The slave device transmits the Explicit Message Response back
to the scanner and is queued into a block transfer buffer.
4. The processor uses a Block Transfer Read file to retrieve the
Explicit Message Response from the scanner’s buffer (upload).
5. The Block Transfer Read file is completed. The transaction IDs
are deleted and can be reused.
The scanner module requires a precisely-formatted block transfer read
and write size of 64 words. The Explicit Message Control table in the
scanner module is 64 words. The scanner module uses the block
transfer size as an indicator that the content is a client/server request.
How to Format the Explicit Message Transaction Block
Ten 32-word transaction blocks within the scanner module are
reserved for Explicit Message Program Control. The transaction blocks
accommodate both the download of Explicit Message Requests and
the upload of Explicit Message Responses.
The scanner module can accommodate one request or response for
each transaction block and can transfer two blocks for each upload
and download. You must format each transaction block as shown in
the following figure:
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