PIC12F629 software USART - Electronic Circuits Projects Diagrams Free

DexterLB · 26th January 2009, 03:00 PM

Hello. I'm using Hi-tech PICC pro and PIC12F629. I want to make a simple usart communication subroutine: I've set Timer0 to make an interrupt every 250 miliseconds. In that interrupt I want to check whether there's an incoming byte from RS232. If there isn't - exit the interrupt and resume normal work. If there is - read the byte in a variable, and start a dialog subroutine. The thing I can't make is the interrupt - how do I check if there's an incoming byte, when I use the soft usart?

**Nigel Goodwin** · 26th January 2009, 05:21 PM

Can't help you with C, but a 250mS timer routine would be useless, you could (and would) miss loads of data in the 250mS.

If you want interrupt driven routines then best to choose a PIC with a hardware UART, otherwise you need to check for the presence of a start bit VERY much more often, depending on baud rate.

A software option would require an interrupt as the start bit begins, which could be done if the PIC supports interrupt from a pin change - this is usually available on PortB (interrupt on change on portb). Check the datasheet, see what the 12F629 has got.

Mike, K8LH · 26th January 2009, 06:02 PM

I posted an interrupt driven 9600 baud half-duplex demo' for the 12F675 here but it's written in assembly language, sorry. It uses IOC (interrupt on change) to detect the start bit leading edge then uses 104 usec interrupts to clock in the data bits.

Regards, Mike

DexterLB · 26th January 2009, 06:41 PM

Hmm, OK. Today I thinked about it and figured out a way how to make it without an interrupt. Thank you for the help anyway

Mike, K8LH · 26th January 2009, 07:06 PM

You should be able to do it without interrupts. You just need to detect the start bit and then clock in data bits by sampling them in the middle of each bit.

Sorry I can't help you out with your particular version of C.

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26th January 2009, 03:00 PM	#1
DexterLB	PIC12F629 software USART Hello. I'm using Hi-tech PICC pro and PIC12F629. I want to make a simple usart communication subroutine: I've set Timer0 to make an interrupt every 250 miliseconds. In that interrupt I want to check whether there's an incoming byte from RS232. If there isn't - exit the interrupt and resume normal work. If there is - read the byte in a variable, and start a dialog subroutine. The thing I can't make is the interrupt - how do I check if there's an incoming byte, when I use the soft usart? __________________ "Humans are stupid."

26th January 2009, 05:21 PM	#2
Nigel Goodwin	Can't help you with C, but a 250mS timer routine would be useless, you could (and would) miss loads of data in the 250mS. If you want interrupt driven routines then best to choose a PIC with a hardware UART, otherwise you need to check for the presence of a start bit VERY much more often, depending on baud rate. A software option would require an interrupt as the start bit begins, which could be done if the PIC supports interrupt from a pin change - this is usually available on PortB (interrupt on change on portb). Check the datasheet, see what the 12F629 has got. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

26th January 2009, 06:02 PM	#3
Mike, K8LH	I posted an interrupt driven 9600 baud half-duplex demo' for the 12F675 here but it's written in assembly language, sorry. It uses IOC (interrupt on change) to detect the start bit leading edge then uses 104 usec interrupts to clock in the data bits. Regards, Mike

26th January 2009, 06:41 PM	#4
DexterLB	Hmm, OK. Today I thinked about it and figured out a way how to make it without an interrupt. Thank you for the help anyway __________________ "Humans are stupid."

26th January 2009, 07:06 PM	#5
Mike, K8LH	You should be able to do it without interrupts. You just need to detect the start bit and then clock in data bits by sampling them in the middle of each bit. Sorry I can't help you out with your particular version of C.