Jason Neudorf wrote: >Neat. I'll be sure to avoid using my Palm IIIxe at 150C. :) > >My purpose was debugging and troubleshooting a hard real-time device the >company is developing for a customer. Just an extra trace to the ICSP >connector, and I can hook in an LED and see which fail-safe has kept the >device from smoking. I was already updating a DAC at 19531, so bit-banging >the IR at that rate was no problem; getting it exact would have caused no >end of troubles. > >How hard would it be to bit-bang the receive, with absolutely minimal >hardware? > You could use the PWM output for this. Stef Mientki > >Jason Neudorf > >----- Original Message ----- >From: "Nigel Orr" >To: >Sent: Thursday, March 13, 2003 10:18 AM >Subject: Re: [PIC]: Doing modulated IR with 16F628 internal clock > > > > >>pic microcontroller discussion list <> wrote on Thursday, March 13, 2003 >>2:10 PM: >> >> >> >>>I've had success with 19531bps masquerading as 19200bps. >>>1.7% worked well >>> >>> >>A typical UART looks for the rising edge of the start bit, then samples >> >> >the > > >>signal a couple of times around where the centre of each bit should be. >>For example, it could look at 25%, 50% and 75% of the way through each >> >> >bit. > > >>That helps to get rid of glitches. >> >>However it means that by the end of the byte (about 10 bit slots later), >>the receivers guess of when the bit starts and stops has to be within 25% >>of a bit period, so each bit can slip by 2.5% of a bit period. For the >>next byte, the UART will re-synchronise on the next start bit, so errors >>aren't accumulated. >> >>In other words, for the hypothetical UART described above, the clocks at >>the receiver and transmitter have to be in agreement within 2.5%, so each >>one needs to be within 1.25% of the correct value to make comms reliable. >>Different UARTs use different sampling schemes, and could even >>resynchronise during the byte (do any do this?), but assuming the clocks >>have to be accurate to less than 1% is a good place to start. >> >>If both clocks are 30ppm crystals, their maximum combined error at room >>temperature is 0.06%, so you can get away with a bit rate error of 1.7%. >>Add a significant temperature difference between the crystals (some of >> >> >what > > >>we do here has > 150 deg C between them!) and your 19531 might not work >> >> >any > > >>more :-) >> >>Nigel >> >> > >-- >http://www.piclist.com hint: PICList Posts must start with ONE topic: >[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads