Allen-Bradley Compact I/O 1769-ADN DeviceNet, Руководство пользователя

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Publication 1769-UM001B-EN-P - October 2002
C-2 1769-ADN Throughput Characteristics
Note: The following equations represent the 1769-ADN
turn-around time using a discrete input (1769-IQ16) and output
(1769-OV16) pair wired in a loop-back fashion. For this
configuration, the settling/filter time of the two modules is 8.6ms
on average
1
. For other I/O modules, consult the appropriate
product installation instructions to determine the appropriate
filter times to use. Modules that consume/produce more than
one word of data will have a slightly increased timing as well.
Minimum Inter-Scan Delay
(ISD) for Polled
Connections
For mid to large 1769-ADN systems that are going to be scanned with
a polled connection, it is critical that the following polled-response
time (t
pr
) be calculated to make sure that the scanner’s inter-scan
delay (ISD) is set correctly to ensure the proper behavior of the
connection.
If the ISD is set lower than the time it takes the 1769-ADN to return its
response, connections will exhibit undesirable behavior (e.g.
intermittent connection dropout).
Note that the presence of higher priority traffic on the network will
require the ISD to be further increased to maintain a robust
connection.
1 The 1769-IQ16 has a nominal filter time of 8ms, and the 1769-OV16 turn-on/turn-off times average out to
0.6ms.
2 Input/output update messages that contain more than 8 bytes will result in fragmented transmission on the
DeviceNet network.
Baud Rate t
tat
a
in ms; i = Number of Input Bytes Configured
in Node (from I/O Summary Tab)
125K bps t
tat
= 0.18
*
i + 8.6
250K bps t
tat
= 0.10
*
i + 8.6
500K bps t
tat
= 0.07
*
i + 8.6
a
t
tat
= turn-around time
Baud Rate t
pr
a in ms; i = Number of Input Bytes Configured
in Node (from I/O Summary Tab)
125K bps t
pr
= 0.16
*
i + 0.4
250K bps t
pr
= 0.09
*
i + 0.4
500K bps t
pr
= 0.06
*
i + 0.4
a
t
pr
= polled-response time