Re: Autobauding

[marcus]

Hello,

i want to implement an autobauding (detect the baudrate automaticly) on an PIC 18f452. How can i do this just with
the UART ? I cant modify the PCB.
I know that the first chars are "AT<CR>".
(Do you know what i try to implement ?)
Thanks.
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This message was ported from CCS's old forum
Original Post ID: 5555

[Sherpa Doug]

:=
:=Hello,
:=
:=i want to implement an autobauding (detect the baudrate automaticly) on an PIC 18f452. How can i do this just with
:=the UART ? I cant modify the PCB.
:=I know that the first chars are "AT<CR>".
:=(Do you know what i try to implement ?)
:=Thanks.

I think you have to read the serial line as a direct input bit, bypassing the UART. Trigger on the Start bit, read the length of the Start bit plus any adjacent bits in "A", calculate the baud rate.
It ain't nice but it is the only way I know. I prefer to avoid autobauding entirely.
___________________________
This message was ported from CCS's old forum
Original Post ID: 5558

[Neutone]

:=
:=Hello,
:=
:=i want to implement an autobauding (detect the baudrate automaticly) on an PIC 18f452. How can i do this just with
:=the UART ? I cant modify the PCB.
:=I know that the first chars are "AT<CR>".
:=(Do you know what i try to implement ?)
:=Thanks.

If you have enough incoming data you can detect framin errors in bytes and switch baud rate untill you have recieved data with a low ratio of framing errors.

if(bit_test(RS232_ERRORS,2)) // Check for framing errors
{RS232_ERRORS=0;
++FramingErrorsCount; // increment count of errors
if(bit_test(FramingErrorsCount,5)) // if 32 errors
DynamicBaud();} // change baud

I clear error count on recieving a good packet.
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This message was ported from CCS's old forum
Original Post ID: 5588

[Dan Mullin]

:=
:=Hello,
:=
:=i want to implement an autobauding (detect the baudrate automaticly) on an PIC 18f452. How can i do this just with
:=the UART ? I cant modify the PCB.
:=I know that the first chars are "AT<CR>".
:=(Do you know what i try to implement ?)
:=Thanks.

Neutone has it right. However, I would skip running interrupts until the baud is determined. Once you find the correct rate set up your interrupts.

//Automatically adjusts baud rate to incoming serial stream.
void Autobaud() {
int fail_cnt, dummy, index, out_loop;
for( out_loop = 0; out_loop < 5; out_loop++ ) {
switch( out_loop ) {
case 0 : set_uart_speed( 57600 );
break;
case 1 : set_uart_speed( 38400 );
break;
case 2 : set_uart_speed( 28800 );
break;
case 3 : set_uart_speed( 19200 );
break;
case 4 : set_uart_speed( 14400 );
break;
}
fail_cnt = 0;
for( index = 0; index < 25; index++ ) {
dummy = getc(); // wait for a byte from serial
if( bit_test(RS232_ERRORS, 2)) // if a framing error then
fail_cnt++; // increment count
}
if( fail_cnt < 6 ) // if less than 20\% FE
return; // found baud so exit
}
set_uart_speed( 9600 ); // else default to 9600
}
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This message was ported from CCS's old forum
Original Post ID: 5678

[Acetoel]

Hi Sherpa Doug,
I need to do autobouding. I rcv 0x55 from a device, but I don't know the speed the device could send that 0x55. I have 35ms after the next byte. How can I measure the Start Bit using the HUART? Do you have a piece of code for that?

Thanks
Ezequiel

:=:=
:=:=Hello,
:=:=
:=:=i want to implement an autobauding (detect the baudrate automaticly) on an PIC 18f452. How can i do this just with
:=:=the UART ? I cant modify the PCB.
:=:=I know that the first chars are "AT<CR>".
:=:=(Do you know what i try to implement ?)
:=:=Thanks.
:=
:=I think you have to read the serial line as a direct input bit, bypassing the UART. Trigger on the Start bit, read the length of the Start bit plus any adjacent bits in "A", calculate the baud rate.
:=It ain't nice but it is the only way I know. I prefer to avoid autobauding entirely.
___________________________
This message was ported from CCS's old forum
Original Post ID: 12608