PIC16F877

[bchicta]

Dans la PIC16F877, il y a un seul USART donc une seul connexion RS232 (pins C6 et C7 du port C), mais dans mon projet j'ai besoin des plusieurs connexion RS232. De manière Soft, comment peut programmer cette connexion à l'aide des autres pins normaux ?


Translation to English:
In the PIC16F877, there is one USART therefore a single RS232 connection (pins C6 and C7 of the port C), but in my project I need several RS232 connections. So in software, how can I program these connection using other normal i/o pins?

[asmboy]

Do the serial ports all have to operate asynchronously
or could you multiplex and use one port at a time?

[Mike Walne]

What sort of baud rates are you wanting for the other UARTS?

Mike

[PCM programmer]

See these threads about multiple software UARTs:
http://www.ccsinfo.com/forum/viewtopic.php?t=40246
http://www.ccsinfo.com/forum/viewtopic.php?p=66711
http://www.ccsinfo.com/forum/viewtopic.php?p=98433

http://notes-application.abcelectronique.com/003/3-5824.pdf

Brush Electronics used to sell source code to do multiple software UARTs
on a PIC (for CCS), using interrupts. But I don't see that product on
his website now. I don't know if he still sells it. He called it "Software
Emulated UART drivers".
http://www.brushelectronics.com

[John P]

Key questions are how many serial ports do you need, how fast must they run, and (most critical) will they potentially all transmit asynchronously? The most difficult operation is receiving data on multiple incoming ports at the same time.

[asmboy]

Lastly as to the maximum COUNT of software UARTS that is safe and reliable to deploy?

In my experience the answer is ZERO.

[PCM programmer]

That's referring to CCS soft UARTs, I assume. What about interrupt-
driven soft uarts, that sample each bit, 3 or more times per bit, in a
Timer interrrupt routine ?

[John P]

That was my point. At 115200 baud, it's not too likely. At 9600, there's a possibility.

People asking for advice on boards like this always take care to leave out the important information.

[asmboy]

I have been happy with dual hardware UARTS IN a PIC
but never felt safe with soft uarts, even when interrupt driven.

Perhaps with a 40 mhz or greater Fosc and timer based bit testing , MAYBE then, ......

but it is not worth it to risk a commercial product and my reputation with flaky data handling, which is what I feel soft UARTS represent.

And adding multiple interrupts to the program just ups the soft uart risk.

But for a SOLID 8 channels of 115200 baud ????

I would rather put the effort into a design based on the Philips SCC2698B
parallel mated to an 18f872x @ 40 MHz.

In THAT approach- I would have total confidence, since you have a total of 10 UARTS, all interrupt capable, and the SCC chip ports, all deeply buffered, and a controller PIC possessing enough ram && MIPS, to process the data you receive.


soft uarts are a hobbyist grade concept, but

NOT IMHO, for any product of any kind, unless perhaps @ 300 baud .