Problem with SX/B compiler using the PAUSE and SEROUT statements

tdodds

·HELP!
I need to have a time delay before sending a character string at powerup as part of my application. When I added the PAUSE statement·to·my code to get the delay, I·kept getting a garbled initial character. After a lot of trial and error, I pared the code down to a bare minimum and found that if the·PAUSE comes first, there is a garble every time on powerup, and if the SEROUT comes first, there is never a garbled initial character. Here is my test code:

This works just fine:

DEVICE········· SX28, OSCXT2, TURBO, STACKX, OPTIONX, BOR26
IRC_CAL··IRC_SLOW
FREQ··········· 20_000_000
PROGRAM START
START:
OUTPUT RA.1
MAIN:
SEROUT RA.1,T9600,71
PAUSE 254
GOTO MAIN

This produces an initial garbled character on powerup every time:

DEVICE········· SX28, OSCXT2, TURBO, STACKX, OPTIONX, BOR26
IRC_CAL··IRC_SLOW
FREQ··········· 20_000_000
PROGRAM START
START:
OUTPUT RA.1
MAIN:
PAUSE 254
SEROUT RA.1,T9600,71
GOTO MAIN

Is this an SX/B compiler bug? How can I get rid of this garble and still get an initial time delay before sending after a power up??

·

Bean

First of all you don't have to set the pin to an output. The SEROUT command will do that.
As for the garbled character, you should set the pin to the "idle" state before the pause.
Since you are using "true" serial mode that would be high.

Try this

HIGH RA.1
MAIN:
PAUSE 254
SEROUT RA.1,T9600,71
GOTO MAIN

Bean.

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·

Jon Williams

Maybe you need a pull-up on your serial line so that it's in a stable state (vis-a-vis your receiver) until the SX can start transmitting on it.· You could enable the weak pull-up on RA.1 like this

· PLP_A = %1101

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Jon Williams
Applications Engineer, Parallax

tdodds

Thanks so much you guys!

I tried your suggestions - and they both fix the problem. Like most problems, it's obvious once it is solved, though I wish I could have had this info before I spending three hours trying different code configurations. It makes sense that the send data lead needs to be put in a steady mark (high) condition immediately on startup. I think this needs to be included in the SEROUT documentation.

Thanks again.

Jon Williams

I don't like to burden our documentation unnecessarily, but will consider adding a note to the modes section·that serial I/O pin *may* need a pull-up or pull-down for proper operation of the attached device.

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Jon Williams
Applications Engineer, Parallax

Post Edited (Jon Williams (Parallax)) : 5/9/2006 11:04:35 PM GMT

James Newton

tdodds, Feel free to add that documentation to an appropriate page on the sxlist.com wiki/blog site. We like our docs heavily loaded with the things users actually trip up on.

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