Siemens CP 243-2 Operations Instructions download pdf (Page 10)

10

Bus

Star

Tree

Master

Master

Master

Bus, star, or tree

AS-Interface network

configurations are possible

Small volumes of data

AS-Interface has been optimised for vol-

umes of data that correspond precisely

to the requirements of the lowest field

level. The structure and length of the

data frame is fixed. Up to four useable

Input bits and four useable Output bits

are exchanged between a slave and the

master in any one cycle.

Real-time requirements

The maximum cycle time, i.e. the time

that a master takes until a node is polled

again is a maximum of 5 ms for a fully

utilised system with up to 31 standard

slaves. In a fully utilised AS-Interface

system according to the extended spec-

ification 2.1, the maximum cycle time is

10 ms for 62 slaves. In most control sys-

tems this time meets the “tough real-

time requirements”. Polling procedures

are deterministic, i.e. the master

“knows” that it can access the current

data of each node connected to the AS-

Interface network within a certain time.

Data transmission

Simple two-wire cables without shield-

ing or PE conductor are used to carry

both data and the auxiliary power for the

sensors simultaneously. The intelligent

data protocol is structured in such a way

that the entire system is extremely in-

terference resistant. Shielding is there-

fore not necessary.

The yellow profiled AS-Interface cable

has become a characteristic feature of

AS-Interface. Its innovative contacting

system (insulation displacement tech-

nology) makes it simple and efficient to

assemble. An AS-Interface network can,

of course, also be configured with stan-

dard circular conductors. For economic

reasons, however, the ribbon cable is

the preferred option.

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