Siemens SIMATIC S7-300 Series Reference Manual page 41

1.4.1 CPU 312 IFM
Special Features
S Integrated I/Os (Wiring via 20-pole front connector)
S No backup battery and therefore maintenance-free
S An S7-300 with CPU 312 IFM can be mounted only on one rack
Integrated Functions of the CPU 312 IFM
Integrated Functions
Process interrupt Interrupt input means: inputs configured with this function trigger a process
interrupt at the corresponding signal edge.
Interrupt input options for the digital inputs 124.6 to 125.1 must be programmed
in STEP 7.
Counter The CPU 312 IFM offers these special functions as an alternative at the digital
inputs 124.6 to 125.1.
For a description of the special functions "Counter" and "Frequency meter",
Frequency meter
please refer to the Integrated Functions Manual.
"Interrupt Inputs" of the CPU 312 IFM
If you wish to use the digital inputs 124.6 to 125.1 as interrupt inputs, you must
program these in STEP 7 in the CPU parameters.
Note the following points:
S These digital inputs have a very low signal delay. At this interrupt input, the
module recognizes pulses with a length as of approx. 10 to 50 ms. Always use
shielded cable to connect active interrupt inputs in order to avoid interrupts
triggered by line interference.
Note The minimum pulse width of an interrupt trigger pulse is 50 ms.
S The input status associated with an interrupt in the input process image or with
LPIB always changes with "normal" input delay of approx.3 ms.
PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP
A5E00111190-01
Description
CPUs
1-25