FIRST SCAN vs reboot

Does First Scan (FST_SCN) happen only after reboot? OR whenever Stop and Start?
I want to test the code but don't know what I have to do to get it to be set.

Can I warm boot the PLC? Or do I have to power cycle it?
(GE Fanuc PLC Micro).

babahu said:

Does First Scan (FST_SCN) happen only after reboot? OR whenever Stop and Start?
I want to test the code but don't know what I have to do to get it to be set.

Can I warm boot the PLC? Or do I have to power cycle it?
(GE Fanuc PLC Micro).

Click to expand...

I am not very familiar with the Fanuc Micro, but as a general rule PLCs turn on the First Scan when powered up, and when going from Program to Run. The information should be in the manual. If it is a Series 90 Micro the manual is here;

http://www.ge-fanuc.com/infolink/manuals/gfk1065f.pdf

The First Scan is listed at the top of Page 9-7 in Table 9-4.

I am sure someone with more GE PLC experience will set you straight.

Stu.....

%S001 (FST_SCN) is true for one scan whenever the PLC changes from stopped to running. It makes no difference if the transition was caused by the run/stop switch, by the programming software, or by turning the power on.

First scan

I do agree with above reply.

When you put controller from Stop to Run , then Controller starts working. during that instance, First scan marker activates (1) for a very small time (its rising edge)
& deactivates immediately.

if You are looking to Application, you cannot even recongize when it appears but it functions fine.

Hope this helps

You should test it with an Add instruction.

Add %R2000 and a constant of 1 to %R2000. If %R2000 has a value of 0, stop and start the plc. Watch the value increase as you test power cycles and stop to run transitions.

Testing code is fundamental to writing code.

Related thread: http://www.plctalk.net/qanda/showthread.php?t=55702