speed sci

[Dietrich]

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Posted: Wed Feb 9, 2005 5:02am

Subject: speed sci
 
    Hello

I use a 8Mhz quartz for my micro. I have Fbus=4MHz

i can use 9600 and 19200 for speed baudrate. But 38400 don't work because 4000000/16/38400 is not an integer.
Is there is an other meaning to have a baudrate at 38400 without changing fbus?

Thank you very much

Regards

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Posted: Wed Feb 9, 2005 8:28am

    Worse case, you only have to be within 5% on timing at each end of an
RS232 connection.

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Posted: Wed Feb 9, 2005 8:49am

You are right for a asynchronous communication, but Pascal case is about 10%
and so out of limits.

No problem if you have to communicate two identical devices at such not
standard resulting speed, but communication with other devices, as a PC,
should fail.

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Posted: Wed Feb 9, 2005 9:22am
 
    It is usually best to avoid this problem by choosing the correct crystal
frequency to start with unless there is some over whelming reason to operate
with an oddball crystal frequency. If that is the case, you simply have to
accept the fact that you will not be able to achieve standard SCI baud
rates.

Possible solutions include using an external UART with its own dedicated
baud rate crystal which would be very difficult to do on the kx8 (no
external parallel bus) unless you were to consider something like the
MAX3100 which uses a SPI interface.

Best wishes

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Posted: Wed Feb 9, 2005 9:40am

    Thank you very much everybody for your help.

This is what i was thinking

Message Edited by Dietrich on 01-29-2006 11:24 AM