Re: [oc] usart

[setan_003@hotmail.com]

----- Original Message ----- 
From: pratheeshks2003@y...  
To: basu081@r... , cores@o...  
Date: Tue, 4 Mar 2003 08:04:33 -0100 
Subject: [oc] usart 

> 
> 
> Respected sir, 
> 
>                   my name is pratheesh,i am studying in 
> madurai(taminadu) 
> for Msc(EC),i am doing one project in usart(8251),i kindly requist 
> your 
> help, i need what are the clock frequency,on what basics it is 
> selscting ,i hope you will surely help me, iwant to complete before 
> the 
> end of march, 
> yours faithfully 
> pratheesh 


                                                                                             
Wednesday, July 02, 2003     
Dear prathes,
I can clear your doubt. I believe, following information  will answer 
your question.    


How to provide clock frequency for the 8251 USART

If  you use 8251 USART  for async Serial communication purpose  you 
must be provide clock frequency by two ways. First  requires chip clock 
frequency for internal timing.it must be at least 30 times the data bit 
rate of the receiver or transmitter. This clock frequency must be apply 
clk pin of the 8251 chip. Next you must be provide transmit clock 
[TxC] & receive clock [RxC] for respectively get serial output and serial 
input. In the Synchronous mode the baud rate of the transmitter and 
receiver, which are the shift rate of the shift registers, are the same as 
the frequencies of the signals applied to TxC and RxC respectively. But 
in the asynchronous mode the three remaining possible combinations 
for the two LSBs  in the mode register dictate the baud rate factor. The 
relationship between the frequencies of the TxC and RxC clock inputs 
and the baud rates of the transmitter and the receiver is: 

            Clock Frequency = Baud Rate Factor × Baud Rate
                                           
                                                                   If  1 0  is in the LSBs of 
the mode register and the transmitter and receiver baud rates  are to 
be 300 and 1200 respectively, then the frequency applied to TxC  
should be 4800Hz and the frequency at RxC  Should be 19.2 kHz .   

Format of the Mode Register [Asynchronous mode]

  MSB	LSB












        
Prathes do you want  more information  about 8251 USART,  please 
contact with me.
                        
                                                     
Thanks.         
K.Elil                                                                                    
   	                       
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