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rs232 with 7bit 2stop bit

 
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reini



Joined: 15 Jul 2005
Posts: 1

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rs232 with 7bit 2stop bit
PostPosted: Fri Jul 15, 2005 10:15 am     Reply with quote
help! how can you use the integratet UART with 7bit and 2stop bit?
PIC18F4550. I did not find any information to any PIC with UART.
Humberto



Joined: 08 Sep 2003
Posts: 1215
Location: Buenos Aires, La Reina del Plata

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PostPosted: Fri Jul 15, 2005 10:36 am     Reply with quote
http://www.ccsinfo.com/forum/viewtopic.php?t=20501&highlight=rs232+stop

Best wishes,

Humberto
ckielstra



Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

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PostPosted: Fri Jul 15, 2005 11:01 am     Reply with quote
There is no direct support for 7N2, both in hardware or software UART. It is easy to simulate when you realise that a stop bit equals a databit with a logic high level. Data is transmitted with the least significant bit first. The trick is to configure RS-232 for 8N1 and make sure to set the most significant bit (MSB) for every byte sent.

Code:
#use rs232(baud=9600, xmit=PIN_TX, rcv=PIN_RX, parity=N, bits=8)

// Function to send data as 7 bits, 2 stop bits.
void Put7N2(int8 Databyte)
{
  bit_set(DataByte, 7);  // Simulate an extra stop bit by setting the MSB
  putc(DataByte);
}

void main()
{
  printf(Put7N2, "Hello world.\n\r");
 
  while(1)  ;   // Loop forever, prevent the processor going to sleep
}


Note: I haven't tested this code, but you get the idea.
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