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GFK-0825F Chapter 4 Operation 4-7
4
BIU Backplane Scan Time
The backplane scan time for the Genius BIU depends on: the type and number of modules present
in the Field Control station, the scan time of the Genius bus, and the number and type of Group
Data Move definitions.
Shorter Genius bus scan times typically impose more overhead on the BIU, increasing backplane
times. Longer Genius bus scan times tend to reduce the overall load to the BIU and thus slightly
decrease backplane scan times.
An estimate of backplane scan times can be found using this equation:.
Backplane scan time (mS) = ( I/O X ( 0.8 + ( 2.25 / Genius Bus Scan ) ) ) + Groups + MFP + 1
In the equation:
I/O = 0.150 X number of conventional module discrete (I and Q) bytes
+ 0.500 X number of conventional module analog (AI and AQ) words
+ 0.090 X number of intelligent module discrete (I and Q) bytes
+ 0.150 X number of intelligent module analog (AI and AQ) words
+ 0.500 X number of I/O modules
Groups = .0.015 X number of bytes, internal BIU table moves
+ 0.093 X number of bytes, BIU / module moves
+ 0.175 X number of bytes, module to module moves
MFP = MFP logic sweep time (if MFP synchronized)
Example 1:
Four modules, no Group Data Moves. Genius bus speed is 47mS.
Slot Module Data per Module Time per
word / byte
Total Time
in mS
1 16-Point Grouped Analog Input
Module (IC670ALG240)
16 words AI
11 bytes I
2 bytes Q
.150
.090
.090
2.40
0.99
0.18
2 Conventional discrete output module 2 bytes Q .150 0.30
3 Conventional analog output module 4 words AQ .500 2.00
4 RTD Input module 4 words AI
4 bytes I
1 byte Q
4 words AQ
.150
.090
.090
.150
0.60
0.36
0.09
0.30
+ number of modules ( 4 ) .500 2.00
= Total I/O 9.52
9.52 X ( 0.8 X ( 2.25 / 47 mS ) ) 8.07 mS
+ Groups (none) 0.00
+ Micro Field Processor (none) 0.00
+ 1.00
Estimated backplane scan time 9.07 mS