Hardware Manual for the PCD3 Series│Document 26/789; Version E 5│31.01.2005
Saia-Burgess
Controls Ltd.
Interrupt inputs
PCD3.Mxxx0 Classic CPUs and expansion housings
3-30
3
3.17
Interrupt inputs
3.17.1 Basics
Because of the input filters and the effect of the cycle time, the digital input modules
are not suitable for immediate reaction to events or for rapid counting processes.
Some CPUs have interrupt inputs for this purpose.
When a positive edge is detected at the interrupt input, an associated XOB is called
(e.g. XOB 20). The code in this XOB defines how the unit should react to the event,
e.g. by incrementing a counter.
The code in XOBs called from interrupt inputs must be kept as brief as possible to
allow enough time between the interrupts to process the rest of the user program.
i
Many FBoxes are intended for cyclic invocation and so not suitable for use in XOBs,
or only in a limited way.
Exception: the FBoxes in the Graftec family (standard library) are well suited
3.17.2 PCD3.Mxxx0 interrupt inputs
The two interrupt inputs are located on the motherboard and can be connected via
the 8-pole, plug-in terminal block (terminals 1 to 8). Source operation is always used.
Interrupt
input
XOB called in case of a
positive edge
Read input directly
INT0
XOB 20
I 8100
INT1
XOB 21
I 8101
Operation:
When a positive edge is detected at input
INT0
,
XOB 20 is
called. The reaction time
up to the XOB 20 call is a maximum of 1 ms. The code in these XOBs defines how
the unit should react to the event, e.g. by incrementing a counter (input frequency
max. 1 kHz where pulse/pause each 50%, total of the two frequencies max. 1kHz).
If the relevant XOB is not programmed, the ERROR LED is switched on or XOB 0 is
called.
10k
10k
4k7
µC
CF 5272
WD
+24V
WD
1
2
3
4
5
6
7
GND
INT1
INT0
Input signals:
H = 15...30 V
L = -30...+ 5 V or not connected
Source operation
4.7 nF
/D
D
8
