Determining Tsno-Bt; Determining Tbtx - Allen-Bradley 1747-SN User Manual

Determining T
SNo-bt
Use the following table to find T
configuration.
Important:
The times shown are, to the best of our knowledge, the
maximum delay times of the scanner. However, in
instances that throughput is an important consideration,
test the application thoroughly first to ensure proper
operation. Note that in most situations the average
throughput is much better than the calculated maximum
throughput.
Number of Logical
Normal Mode
Racks Racks
All Baud Rates
Configured
1 Logical Rack 16.0
2 Logical Racks 19.0
3 Logical Racks 22.0
4 Logical Racks 25.0
See page A-12 if you are not sure how to determine the number of logical racks configured.
Determining T
btx
Before determining (T
btx
write or read length that is to be processed by each logical rack on
the RIO link. RIO scan time is increased each time an BT is sent to
any logical device on the RIO network. The scan time increase
depends on the number of words sent in the BT and the selected
baud rate.
RIO link protocol allows for a maximum of one BT to be sent to
each logical rack on the RIO link during any single RIO scan.
Therefore, if multiple BTs are sent to devices within the same logical
rack, only the longest BT to that logical rack needs to be considered
to determine your maximum throughput. The RIO scan time
increase (T ) for each logical rack is:
ri
Baud Rate RIO Scan Time Increase (T
57.6K baud 0.300 x BT length + 5.0 ms
115.2K baud 0.150 x BT length + 3.5 ms
230.4K baud 0.075 x BT length + 2.0 ms
The total increase in the RIO scan time (T
T = sum of T for all logical racks
btx ri
Specifications
for your particular
SNo–bt
Complementary Mode
57.6K baud 115.2K baud
19.0 24.0
23.0 27.0
26.0 30.0
28.0 34.0
), you need to establish the maximum BT
)
ri
) is equal to:
btx
Publication 1747 6.6 - July 1996
A–7
230.4K baud
32.0
36.0
39.0
42.0