I/O Problem

TomS

I'm trying to use SHIFTOUT and PULSOUT. When I use pins 0 - 7 for output everything works fine. But when I try to use pins 8 - 15 nothing comes out. What gives?

Tom

Newzed

We can't tell without your COMPLETE code, including pin assignments.

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Sid Weaver
Do you have a Stamp Tester yet?
http://hometown.aol.com/newzed/index.html

·

PJAllen

Well, you didn't included your programming, so I'll guess that you aren't setting up pins 8-15 as outputs beforehand.· I'm figuring that using SHIFTOUT and PULSOUT aren't the same as OUTPUT (which makes the pin associated an output regardless.)· Maybe you're declaing P0-7 as outputs, but not P8-15.

TomS

I've reduced the program to the following:

' {$STAMP BS2P}
' {$PBASIC 2.5}
Main:
PULSOUT 15, 10
PAUSE 20
GOTO Main

It works as long as the first argument of PULSOUT is <= 7.
I've tried setting the pin to OUTPUT but it doesn't do any good.

Jon Williams

How do you know it's not working? Have you looked at the output with a 'scope. BTW, there is no need to use OUTPUT ahead of PULSOUT, but you will want to use LOW or HIGH -- PULSOUT inverts the state of the selected pin for the duration. If you want a high-going pulse on one of the pins, initialize that pin with LOW.

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Jon Williams
Applications Engineer, Parallax

TomS

I'm using an oscilloscope to view the output.

Tracy Allen

How is the BS2 mounted? I.e., is it on one of the Parallax development boards, or in a custom circuit? Anything attached to the pin? How about if you use simple HIGH and LOW commands?

' {$STAMP BS2P}
' {$PBASIC 2.5}
DO
HIGH 15
INPUT 15 : DEBUG BIN1 IN15
LOW 15
INPUT 15 : DEBUG BIN1 IN15
LOOP

What do you see on the 'scope, and what do you see on the debug screen (without the 'scope probe attached)?

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Tracy Allen
www.emesystems.com

TomS

The BS2 is on a Parallax board, two days old.

Your code yields alternating 1's and 0's on the Debug screen. Still nothing on the output. I've also tried using an alternate connector but get the same results.

Tracy Allen

Try placing the 'scope probe directly on the pin on the 24-pin Stamp module. That is physical pin 20, logical pin p15. The fact that you are getting alternating 0s and ones indicates that the BS2 is working, but maybe there is an open circuit somewhere else.

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Tracy Allen
www.emesystems.com

TomS

There are some problems with the BS2p. On pin 20 I had a pulse with normal rise time and a RC decay for the return to low. I measure an open ciruit between pin 20 on the chip and pin 20 on the board (bs2p demo board) I removed the bs2p but couldn't see any obvious problems. Looks like a bad board/and/or bs2p. When I put the bs2p back in I lost all on one of the connectors. Even pin 1 looks lousy. I guess I'll have to return it.

Tracy Allen

If you have the 'scope probe on p15 while running the program that goes HIGH 15 : INPUT 15 : LOW 15, you will in fact see an RC decay from high to low, as the small capacitance of the pin discharges through the input resistance of the 'scope.

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Tracy Allen
www.emesystems.com

Jon Williams

If you're using a BS2p24 on the BS2p24/40 demo board then the P8..P15 pins are actually connected to the A8..A15 sockets -- there's a note about this on the last page of the documentation.

Docs: http://www.parallax.com/dl/docs/prod/boards/BS2p2440DBrd.pdf

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Jon Williams
Applications Engineer, Parallax

TomS

You are, of course, correct. I had the documentaion dated 10/2002 and it didn't say anything about it. The file you pointed me to is dated 10/2004.

Thanks

Jon Williams

Sorry for the confusion -- back in 2002 we had separate demo boards for the -24 and the -40; it ultimately made sense just to sell one.

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Jon Williams
Applications Engineer, Parallax