PushButton control of two LEDs
LisaQ
Posts: 33
Attached is a sample program from What's a microcontroller.·I understand the PAUSES in the IF and ELSEIF- they toggle the LEDs.·I don't understand why there is a pause for 50mS after the ELSE. I commented out the PAUSE and reran it- I didn't see any difference. Could someone explain it for me?
Comments
They might be there to slow down or regulate DEBUG message printing.
In any case, they don't seem necessary.
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Chip Gracey
Parallax, Inc.
I thought I was just missing something·that may have been significant.
Lisa
If you remove the PAUSE 50 in the ELSE block, the serial messages that report the pushbutton states·repeat more quickly when no buttons are pressed.· At the time the What's a Microcontroller book was written, that lack of pacing·caused software problems in certain computers.· We observed this at some of the computer labs we visited to teach BASIC Stamp Educators Courses.
I added the PAUSE 50 in the·ELSE·code to prevent the problem.· I also reported·that and all my other "in the field" observations·to·the·software engineer·who·develops and maintains the BASIC Stamp Editor.··The combined documentation and software updates·have reduced·trouble-shooting at these courses to zero.· We also see very few tech support calls as a result, and it's great in general because we know that people can focus on what they are learning without being plagued by frozen software, blue screens, etc.
We pay similar attention to these forum posts, and since you asked, we'll keep this discussion on file to make sure that nobody else will wonder about this after the next book revision.·
Andy
P.S.
This code does the same job, and eliminates the need for·the your turn section at the end of the activity.
' {$STAMP BS2}
' {$PBASIC 2.5}
DO
· DEBUG HOME, ? IN4, ? IN3
· IF (IN3 = 1) THEN HIGH 14
· IF (IN4 = 1) THEN HIGH 15
· PAUSE 50
· LOW 14
· LOW 15
· PAUSE 50
LOOP
My rationale in keeping the code you see in the book was that most students (and teachers) would benefit from consistent use of the·IF...ENDIF code blocks, especially in the earlier chapters.· An example of a one line IF...THEN statement can be found in Chapter 7.·
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Andy Lindsay
Education Department
Parallax, Inc.
Post Edited (Andy Lindsay (Parallax)) : 3/1/2010 9:19:10 PM GMT
Thank you for the explanation. It makes me feel better to understand "why".
Now I have another question, won't that code light the LEDs if I'm not pressing a switch? The cathodes are grounded.
Lisa
Regarding "...another question..."· Aach!· It looks like in the 2/24 post, I was crossing my i's and dotting my t's!· Alright, code example changed from:
· ...
· IF (IN3 = 0) THEN HIGH 14
· IF (IN4 = 0) THEN HIGH 15
· ...
to
· ...
· IF (IN3 = 1) THEN HIGH 14
· IF (IN4 = 1) THEN HIGH 15
· ...
It should work correctly now.
Andy
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Andy Lindsay
Education Department
Parallax, Inc.
Post Edited (Andy Lindsay (Parallax)) : 3/1/2010 9:50:41 PM GMT