General setup rules

An ABB AC 31 system always includes an AC 31 central unit. There are three types of central units:

– The 40 series central unit, with a local inputs / outputs extensions interface

– The 50 series central unit, with a local inputs / outputs extensions interface

and a CS 31 bus interface

– The 90 series central unit, with a CS 31 bus interface

Each central unit incorporates a specific number of binary inputs / outputs and occasionally

analog. It is possible, depending on the central unit, to increase the number of inputs / outputs,

to add input / output extensions connected directly to the central units or remote input / output

units via the CS 31 twisted pair.

The interruptions have priority over the main program execution. If all three interruptions are

triggered simultaneously then the interruption triggered by I 62.03 has priority over the I 62.02

input interruption which in turn has priority over the cyclic interruption. Once an interruption has

been launched it cannot be interrupted by another (Figure 1-5).

The execution duration of a cycle (bus cycle + program cycle) is controlled by the central unit.

Any excess of the cycle time defined by the user in AC31GRAF is signaled by the ERR Led, at

the front of the central unit, as of the first program cycle.