Need help with PIC USART programming - Electronic Circuits Projects Diagrams Free

davepusey · 5th July 2009, 04:20 PM

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?

**Nigel Goodwin** · 5th July 2009, 04:22 PM

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.

davepusey · 5th July 2009, 05:20 PM

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.

**Nigel Goodwin** · 5th July 2009, 05:45 PM

Quote:

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.

Quote:

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.

davepusey · 5th July 2009, 06:27 PM

Quote:

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?

chuddleston · 5th July 2009, 06:59 PM

Fr. Tom McGahee

Check out the PICUART.zip example. Enable the UART interrupt and configure the TRIS register correctly for the RX and TX pins, then when a byte is received the code will automatically jump to ORG h'0004'.

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5th July 2009, 04:20 PM	#1
davepusey	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? __________________ Dave Pusey. PIC Programming Tutorials: http://www.mstracey.btinternet.co.uk...al/picmain.htm Brilliant PIC Simulator: http://www.oshonsoft.com/pic.html

5th July 2009, 04:22 PM	#2
Nigel Goodwin	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. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

5th July 2009, 05:20 PM	#3
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 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. __________________ Dave Pusey. PIC Programming Tutorials: http://www.mstracey.btinternet.co.uk...al/picmain.htm Brilliant PIC Simulator: http://www.oshonsoft.com/pic.html

5th July 2009, 06:59 PM	#6
chuddleston	Fr. Tom McGahee Check out the PICUART.zip example. Enable the UART interrupt and configure the TRIS register correctly for the RX and TX pins, then when a byte is received the code will automatically jump to ORG h'0004'.