ABB S800 I/O Manual page 60

Data Scanning
Minimum I/O scan cycle time = 4 ms
For example, a station with CI840, single or redundant, two AI810, one
AO810/AO810V2, two DI810, two redundant pairs of DO840 and one redundant
pair of AI845 will give the following I/O scan cycle time:
Minimum I/O scan cycle time = 4 ms
60
the AI810s and the AO810/AO810V2 every (4*12 ms) 48 ms and the
AI830/AI830A every (10*12 ms) 120 ms.
2 AI810 => 2*3.00 ms =
1 AO810/AO810V2 => 1*1.20 ms =
2 DI810 => 2*0.50 ms =
2 DO840 => 2*1.00 ms =
1 AI845 =>1*6.00 ms =
1 CI840 => 1*2.10 ms =
------------------------------------------------------
18.30 ms is not a multiple of 2, so increase of the value to the nearest multiple
of 2 gives 20 ms.
That will give an I/O scan cycle time of 20 ms between the FCI and its I/O
modules. This means that the DIs and DOs will be scanned every 20 ms, 
the AI810s and the AO810/AO810V2 every (4*20 ms) 80 ms and the
AI830/AI830A every (10*20 ms) 200 ms.
Section 3 Configuration
6.00 ms
1.20 ms
1.00 ms
2.00 ms
6.00 ms
2.10 ms
18.30 ms
3BSE020926-600