Ruth Hendrix

SCI BAUD Rate

Discussion created by Ruth Hendrix Employee on Jan 26, 2006
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Posted: Wed Jun 15, 2005 10:11 am    
 
Hi Guys
I have been looking at the SCI module for the MC9S12C32 and with a Bus CLK of 25MHz the table they supply only goes to 38400 Baud.
Are they making some kind of recomendation not to go above that or you can easily achieve higher rates? By using the formula provided it can go theoretically up to 1500000 baud.
any info/experience apreciated.
Best regards
Posted: Thu Jun 16, 2005 9:48 am  
 
It's usually that there are certain standards (1200, 4800, 9600, 19200 ...) for SCI type communications and 38400 is the highest of these that can be met with a 25MHz bus. Of course going to a "non-standard" baudrate or using a different clock will allow much higher rates.
 
Posted: Thu Jun 16, 2005 12:40 pm    
 
I do know about the standard baud rates, but 153.6 kbaud is also a standard baud rate and acording to the formula given I can achieve it.
What I am asking is:
Is Freescale giving in a roudabout way, a maximum Baud rate for the MC9S12C32.
regards
Posted: Fri Jun 17, 2005 12:32 am    
 
Bus clock of 25MHz? I take it you are using a 25MHz crystal? Are you writing in ASM or C?
Posted: Fri Jun 17, 2005 7:12 am    
 
I am actually using 24MHz as Bus CLK ( from a 16MHz crystal).
The question is still the same, if I can generate baud rates above 34800 Baud, which seems to be possible, will it be usable from the Micro point of view?
regards
Posted: Fri Jun 17, 2005 7:54 am  
 
Hi,

the micro does not have a problem with fast baudrates. There is internal divide-by-16 stage in the SCI, so with bus freq of 24MHz the maximum bitrate you will get is 14M/16=1.5Mbit/s. The micro should be happy with that.
 
Posted: Sat Jun 18, 2005 6:48 am    
 
Hi
That's all I needed to know.
Thanks for your help.
best regards

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