Siemens S7-200 User Manual download pdf (Page 14)

The PLC Cycle (3)

Revision

What you know already...

- A Few Words of Revision

- Here are the Bits

- Current Flow in the Ladder Diagram

- The PLC Cycle

Outputs

modified only at

the end of the

next cycle

Signal changes at inputs taking place during a cycle

are transferred to the input register in the next cycle.

There, the signal states for this cycle are "frozen". This

is the process-image input table PII (see a).

In the next cycle, the transferred states are combined

in accordance with the ladder diagram (see s) and the

outputs are updated in accordance with the results of

the logic operations.

Process-

image of I0.0

State of input

I0.0

State of output

Q0.0

Latching Revision

Pulse-Oper-

ated Switch

Off-Delay

Timer

Sequencer Appendix

Voltage at input changes

from 0 to 24 V

Time until process image

(PII) has status “1”

Time for ladder logic

operations and modification of

the output status

1 2 ... 9 10 11 12 13 14 15 16 17 18 19 ... 73 74

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Siemens S7-200 User Manual Page 14