Dwayne Dietrich

speed sci

Discussion created by Dwayne Dietrich Employee on Jan 29, 2006

This message contains an entire topic ported from a separate forum. The original message and all replies are in this single message. We have seeded this new forum with selected information that we expect will be of value to you as you search for answers to your questions.

 
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
--------------------------------------------------------------------------------
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.
--------------------------------------------------------------------------------
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.
--------------------------------------------------------------------------------
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
--------------------------------------------------------------------------------
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

Outcomes