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Serial communications and stop bits

 
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mauro
Guest
Serial communications and stop bits
PostPosted: Thu Dec 16, 2004 3:48 am     Reply with quote
Hi
Is there a way to set the number of stop bits in serial
communications? Apparently, with high baud rates (115200)
I loose the communication with my device (who uses
a 2 stop bits protocol, while PIC uses 1). Lower baud
rates (9600) are much better (almost 90% of success in
sending messages) but I need to switch to 115200
Thanks in advance, ciao!
mauro
Ttelmah
Guest
Re: Serial communications and stop bits
PostPosted: Thu Dec 16, 2004 4:09 am     Reply with quote
mauro wrote:
Hi
Is there a way to set the number of stop bits in serial
communications? Apparently, with high baud rates (115200)
I loose the communication with my device (who uses
a 2 stop bits protocol, while PIC uses 1). Lower baud
rates (9600) are much better (almost 90% of success in
sending messages) but I need to switch to 115200
Thanks in advance, ciao!
mauro

There is one way of 'cheating' this.
The UART on the PIC, only supports one stop bit. However it supports 9bit comms. If you set the ninth bit, this gets sent as another 'high' bit before the single stop bit, generating effectively two stop bits. The chip will then receive the extra stop bit as the ninth data bit, which can be ignored.
Set the UART up to use 9bit comms, and when you would call 'putc', instead call a 'wrapper' function, like:
Code:

#bit ninth_bit = RS232_ERRORS.7

void putc9(int8 val) {
   ninth_bit=1;
   putc(val);
}


This then ensures the ninth bit is set for each byte, and generates the required effect.

Best Wishes
mauro
Guest
Re: Serial communications and stop bits
PostPosted: Thu Dec 16, 2004 7:33 am     Reply with quote
Ttelmah wrote:

There is one way of 'cheating' this.[...]


thank you very much, it works perfectly!
I had already tried the 9-bit data solution but hadn't
managed to get it working...
ciao and thanks again

mauro
Ttelmah
Guest
PostPosted: Thu Dec 16, 2004 9:37 am     Reply with quote
Glad it worked. :-)
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