Rockwell Automation 1747-ASB Remote I/O Adapter - Manual (Page 137)

Publication 1747-UM006B-EN-P - June 2003
Specifications A-9
Discrete I/O Throughput with Block Transfers Present
The information in this section is used to calculate the discrete
throughput of the 1747-ASB module if either of the following
conditions are true:
•
There are block transfer mapped I/O modules in the 1747-ASB
chassis.
•
There are RIO block transfers occurring on the RIO link to any
chassis.
If RIO block transfers not are present on the RIO link or if the
1747-ASB chassis has no block transfer mapped I/O modules, you
must use the Discrete I/O Throughput without Block Transfers Present
section.
To calculate discrete I/O throughput with block transfers present, use
the following formula:
T
dm-bt
= T
dm-nbt
+ 2T
btx
T
dm-bt
= The maximum 1747-ASB module discrete throughput
with block transfers in milliseconds (ms)
T
dm-nbt
= The maximum 1747-ASB module discrete throughput
without block transfers in milliseconds (ms)
T
btx
= Additional time due to sending any RIO block transfer
data on the RIO link
Before determining (T
btx
), you need to establish the maximum block
transfer write or read length that is to be processed by each logical
device on the RIO link including the 1747-ASB module.
RIO scan time is increased each time an RIO block transfer is sent to
any logical device on the RIO network even if it is not sent to the
1747-ASB module. The scan time increase depends on the number of
IMPORTANT
You will need to use the backplane scan times
located in the top table on page A-6. You must
include the time necessary to scan all the words of
all the I/O modules in the 1747-ASB chassis,
including the block transfer mapped I/O modules.
For example, if a 1746-BAS module is used, (T
b
)
must include the time needed to scan 8 input and 8
output words even though the 1746-BAS module
consumes only 2 bytes in the 1747-ASB image.