Clock Speed and Serial Output

[Iloveoakdave]

Hi all. I just got a CrystalFontz serial LCD (is this thing big or what!) and have it working at 19200 with the #use Delay(20000000). When I change this to 4000000 I get garbage output. I've seen some examples set to 4Meg and 19200 that I assume is working. Any ideas why 19200 does not work at the 4Meg setting or is there some magic formula for clock speed and serial output. I'm using the CCS ICD and their test board. Thanks.

dave

[Neutone]

[SherpaDoug]

If you are using a software UART there may be some compensation for the software execution time. At high baud rates this will be significant and might be a little off at 40MHz.
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[Iloveoakdave]

thanks for the input. I believe the CCS board uses a Maxim device. I will check it out.

[SteveS]

Please take no offense at this dumb question but let me ask:

Did you physically change the oscillator to a 4Mhz version when you changed the delay statement? You don't say anything about the oscillator.

In any case if you did, it may be a bad part or the wrong type (serial vs. parallel). If you didn't, then do.

- SteveS

[Iloveoakdave]

No this is a good question. Since I'm using the CCS demo board I assumed that you could change the delay and it would take care of the rest without physically changing the crystal. I wonder if this thinking is correct.

dave

[SteveS]

The #use delay statement is only a way to let the compiler know what actual crystal you have so it can correctly figure bauds, delays, etc. It does nothing (directly) to the hardware. So you'll need to change out the crystal, oscillator, etc to match the #use delay value to get it to work right.

- SteveS

[Guest]

Good info to know Steve. Thanks.

dave