Refresh Times / Reply Times; Bus Refresh Times; Central Unit Reply Times - ABB AC 31 Technical Manual

3.4. Refresh times / reply times

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Presentation / operation
The central unit interrogates the remote units in order to establish an initial image of the
system configuration during initialization.
The remote units are then interrogated with each bus cycle. This enables the recognition of
newly added or removed remote units and the updating of the diagnosis information.
If the central unit receives a message indicating a CRC8 error it will not be signaled
immediately and the frame will not be taken into account. After nine consecutive transmission
errors a "bus error" is signaled by the central unit. The bus error is also signaled to the remote
units after a 250 ms time-out.
Bus refresh times and central unit reply times depend on the system configuration, the number
and the type of remote units on the CS 31 bus. The bus refresh and the user programs are
executed in series.

3.4.1. Bus refresh times

The bus refresh time corresponds to the transmission time over the bus. The calculation
corresponds to the addition of all the communication times of the remote units on the bus and
the base time of the master central unit which is 2 ms.

3.4.2. Central unit reply times

The central unit reply time corresponds to the time taken to activate an output after the
activation of an input.
The maximum reply time is obtained by adding the filtering time of the input, the bus refresh
time, the delay time for the output and twice the cycle time.
The filtering time for an input on the 40 and 50 series is 5 ms.
The delay time for a transistor output is considered as null in milliseconds and the delay time
for a relay output is 6 ms.
Comment:
The inputs / outputs of central units and their extensions can be accessed, for rapid
processing, independently of the cycle time with the user program functions DI and DO (see
chapter 6).
The cycle time calculation is given in chapter 5 at the cycle time configuration level as well as
the communication times of each unit for the bus transmission times calculation.
ABB Control - AC 31
1SBC 260400 R1001-b 06.99