On 3 Apr 2008 at 18:06, piclist@ian.org wrote:
> I am trying to send data out on the hardware USART of a PIC18F252 from 
> readign the datasheet and it is not sending any data.
> 
> I have the output pin on  scope and when I run the init code it goes high, 
> but when I try to send chartacters, nothing happens.
> 
> Here is the bit of code I am using.  (BoostC compiler)
> 
> 	trisc.6 = 0;     // Set TX pin for output.
> 	trisc.7 = 1;     // Set RX pin for input.
> 	spbrg   = 51;    // 9600 baud at 20MHz clock.
> 	txsta.BRGH = 1;	 // 1 = High baud rate.
> 	txsta.SYNC = 0;	 // 0 = async.
> 	rcsta.SPEN = 1;	 // 1 = Enable the serial port hardware.
> 	txsta.TX9  = 0;	 // 0 = No 9th bit.
> 	txsta.TXEN = 1;	 // 1 = Enable transmission.
> 
> 	while (1)
> 	{
> 		while (!txsta.TRMT)
> 			txreg = 'H';
> 		while (!txsta.TRMT)
> 			txreg = 'i';
> 
> 		porta.1 = !porta.1;
> 	}
> 
> The led blinks (I can see it on the scope) but the TX pin (pin RC6/TX/CK) 
> just stays high and does nothing at all. 
> 
> I assume I don't need to tie the TX pin to ground or voltage?  I am going 
> to another PIC so I don't need to do any RS232 level inversion either.
> 
> Any clues?  Thanks again!

Hi Ian,

Your while loops look wrong. Do you really want to continuously write to txreg until 
the trmt bit goes high? Here's a snippet from one of my projects, was for a 16F 
device but should give you some clues...

TXREG = x;		// Put the byte into TXREG
while(!TXIF);		// Wait for transfer to TSR
while(!TRMT);	// Wait for it to be sent

-- 
Brent Brown, Electronic Design Solutions
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Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
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eMail:  brent.brown@clear.net.nz


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