Mike Harrisons 115.2kBaud with a 4.096Mhz crystal

Mike Harrison says:

While we're on the subject of neat little routines etc...
This code sends a byte at 115.2Kbaud
With a 4.096MHZ xtal, error is about 1.25% (near enough),
with 4.000MHz, 4.55% (marginal).
Data is non-inverted (i.e can be fed straight to PC)
txbyte  
  movwf temp
  movlw d'10'  ; 1 start + 8 data + 1 stop
  movwf cnt
  bcf status,c  ;start bit
  movf portb,w
txloop
  andlw 0ff-(1<<seroutbit)
  skpc
  iorlw 1<<seroutbit
  movwf portb
  sec
  rrf temp ; carry shifted in as stop bit
  decfsz cnt
  goto txloop
  return
Incidentally It's also possible to do 115K2 bit-bashed reception at 4.096MHz, by generating an INT interrupt off the startbit edge, and grabbbing all the data bits within the int code. Context save/restore overheads mean there's only a couple of cycles available to the foreground task if data is streaming in continuously!

file: /techref/microchip/rs232at115kbps.htm, 1KB, , updated: 2000/3/20 10:02, local time: 2008/11/22 02:16,

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<A HREF="http://piclist.org/techref/microchip/rs232at115kbps.htm"> Mike Harrisons 115.2kBaud with a 4.096Mhz crystal</A>

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