Rockwell Automation 1747-SN Remote I/O Scanner - Manual (Page 104)

Publication 1747-UM013B-EN-P - January 2005
A-8 Specifications
Determining Tbtx
Before determining (Tbtx), you need to establish the maximum BT
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 (Tri) for each
logical rack is:
The total increase in the RIO scan time (Tbtx) is equal to:
Tbtx = sum of Tri for all logical racks
Example Discrete I/O Throughput with Block Transfers Present
An SLC 5/03 is using a scanner to control a 115.2K baud RIO link that
has 3 adapters and 4 logical devices.
Number of
Logical Racks
Configured
(1)
(1) See page A-12 if you are not sure how to determine the number of logical racks configured.
Normal Mode Complementary Mode
All Baud
Rates 57.6K baud 115.2K baud 230.4K baud
1 Logical Rack 16.0 19.0 24.0 32.0
2 Logical Racks 19.0 23.0 27.0 36.0
3 Logical Racks 22.0 26.0 30.0 39.0
4 Logical Racks 25.0 28.0 34.0 42.0
Baud Rate RIO Scan Time Increase (T
ri
)
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