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RS232 on 12f675
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PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Thu Jul 29, 2004 12:05 pm     Reply with quote
Quote:
any suggestions?

Yes. The things that we said to do in a previous day
still apply in the present day.
http://www.ccsinfo.com/forum/viewtopic.php?t=19928&postdays=0&postorder=asc&start=16
djpark



Joined: 02 Mar 2004
Posts: 49

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PostPosted: Fri Jul 30, 2004 10:04 pm     Reply with quote
young wrote:
Thank you for help, how to "Double check the accuracy of the internal "crystal""? How do I know if it has about 3% or better reliaility for reliable comms?


The datasheet says the internal RC oscillator is "Precision Internal 4 MHz oscillator factory calibrated to ±1%" and the value is stored at the last byte of the flash.

If you look at the asm output from ccs, you will see that the first instruction at powerup is to call this calibration routine and you can be assured that it is calibrated.

ccs will allow you to setup 38400 baud, but you will get garbage at receiving side. So far all the 12F675 I have have shown very good result of sending continuous data stream at 19200 baud.

One thing to remember is that the software serial driver is very sensitive to the timing and if you have timer interrupt in the middle of transmit, you will get corrupted output, even at 9600 baud. So be sure to arrange your application to send data in between any interrupt.

-- dj
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