Specifications

Detecting Short-circuited End Devices Appendix A: Troubleshooting
104 VisiLogic: Getting Started
Appendix A: Troubleshooting
Detecting Short-circuited End Devices
The controller can detect short circuits in end devices (loads) that are
connected to transistor outputs located on snap-in or expansion I/O modules.
If a short circuit is detected on either an expansion or snap-in I/O module, SB
5 turns ON.
If the short circuit is located on an:
I/O expansion module, the location is indicated in SDW 5.
Snap-in I/O module, the LSB in SDW 6 turns ON.
SDW 5 provides a bitmap. Each I/O expansion module included in your
controller's hardware configuration is assigned a number, 0-7, according to its
place in that configuration. In the bitmap, bits 0-7 correspond to these place
numbers.
In the bitmap below, short circuits have been detected in devices that are
connected to expansion modules 1 and 3.
SDW 5
Please note that although an SW is 32 bits long, only 16 bits are shown below.
Positive Transition Contact ( Rise )
A Positive Transition Contact gives a single one-shot pulse when the bit
operand it is linked to rises from OFF (logic 0) to ON (logic 1).A Negative
Transition Contact gives a single one-shot pulse when the bit operand it is
linked to falls from ON (logic 1) to OFF (logic 0). You can link them to any of
the following bit operands:
Memory Bit
System Bit
Output
Timer
Counter
A cellular phone keypad key is an example of a Positive Transition Contact.
When you push a key a number is displayed on the screen. It does not matter
if you push the key quickly or hold it down for several seconds. The number
will only appear once on the screen.
The cellular phone registers the transition from key NOT pressed to key
pressed. The length of time the key is pressed is not relevant. You must
release the key and press it again to repeat the number on the cellular phone
screen.
During the system scan, a Positive Transition Contact address is evaluated for
a transition from OFF to ON. A transition allows power to flow through the
Positive Transition Contact for one scan.