ABB NIBA-01, Руководство по установке и запуску

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Chapter 5 – Programming
5-4 NIBA-01 Installation and Start-up Guide
Calculating the Optimal
Cycle (Scan) Time
For fast data transfer, the host controller should sent the message
frame (detailed in Chapter 6)
as frequently as possible. However, the
slave stations on the bus may not be able to follow if the cycle time
(scan time) is too short. The cycle time can be calculated using the
following formula:
t
cycle
= ( 13
•
( 6 + n ) + 1.5
•
m )
•
t
Bit
+ t
SW
+ t
PH
where
t
cycle
Transfer time in milliseconds
n Number of user data bytes
m Number of remote bus modules installed
t
Bit
Bit duration (0.002 ms for 500 kbit/s)
t
SW
Software runtime (0.2 ms)
t
PH
Runtime on the transmission medium
(for copper, 0.016 ms
•
l/km,
where l = remote bus cable length in kilometres)
Note: The minimum cycle time with the NIBA-01 is 1 ms.