Rockwell Automation 1747-SDN SLC 500 DeviceNet Scanner Module User Manual - Manual (Page 149)

Publication 1747-UM655B-EN-P - June 2007
Explicit Message Program Control 149
Message lengths and slave device types impact transaction message
completion times. If the processor has queued multiple Explicit
Message Transactions to the module for multiple slave devices, the
transactions with the slaves may not complete in the order in which
the requests were received. The slave responses are queued to the 32
word M1 file transfer in the order in which they are received.
As response transaction blocks are uploaded, the processor’s program
matches the responses to the requests by using the TXID field.
Explicit Message Program Control Limitations
•
The processor is always the DeviceNet client and the slave is
always the DeviceNet server.
•
A maximum of ten Explicit Message Request Transaction Blocks
with the execute command can be queued to the module at any
time. For example, ten M0 file transfers containing one
transactions each, can be queued at any time. The module
receives and deletes any additional client/server requests with
the execute command over the maximum of ten.
Processor
Request
Transaction
Block
Ladder Scans
M1 File Transfer
Response
Transaction
Block
Slave Device
Process Requests
and Responses
1747-SDN Module DeviceNet Network
DeviceNet
Explicit Message
Requests and
Responses
M0 File Transfer
Response
Transaction
Block
Request
Transaction
Block
Response
Transaction
Block
Scanner
Request
Queue
Scanner
Response
Queue
Done or
Error-detached