Thread: Need help with PIC USART programming

Hi

I've got my circuit wired up like this so far...

The red wire acts as a loopback (for testing) so that anything i send out the serial port on my computer, i get straight back again.

This is working perfectly.



The plan is to remove the red link, and connect the TTL level signals to the USART of a PIC16F627 like this...



The question is... How do I program the PIC to send and receive data?

Check my PIC RS232 tutorials, most use a software UART (so it can be used on any pin), but the last one shows how to use the hardware UART.

Ok - a couple of questions...

1) What is the purpose of the test/loop in this code block?

Code:

XMIT_RS232  	btfss   PIR1,	TXIF 	      ;xmit buffer empty?
     		GOTO	XMIT_RS232            ;no, wait
     		MOVWF   TXREG		      ;now send
                RETURN

2) Is there a way to receive data via an interrupt?

I dont really want to keep polling the usart when it wont be used that often.

Originally Posted by davepusey

Ok - a couple of questions...

1) What is the purpose of the test/loop in this code block?

Code:

XMIT_RS232  	btfss   PIR1,	TXIF 	      ;xmit buffer empty?
     		GOTO	XMIT_RS232            ;no, wait
     		MOVWF   TXREG		      ;now send
                RETURN

As the comments say, it's waiting until the transmit buffer is empty - it's the standard way of using the UART - you don't want to overwrite the buffer while it's still been used.

2) Is there a way to receive data via an interrupt?

I dont really want to keep polling the usart when it wont be used that often.

Yes, you can set the hardware UART to generate an interrupt when data is received, or you can occasionally poll the interupt flag to see if data is received.

Originally Posted by Nigel Goodwin

Yes, you can set the hardware UART to generate an interrupt when data is received

Do you have an example of this please?