Jeremy Harris
Senior Member
Worth noting that the standard upon which this whole debacle is based used the principle of synchronising each character with the leading edge of it's start bit, exactly as described in the Rev Ed paper, and exactly as taught to me in college 40 odd years ago.
This point seems to be being lost here with esoteric arguments as to who is right or wrong in any particular interpretation of a non-existent "standard". There isn't, as far as I'm aware, an internationally recognised standard for 5V level serial data comms using RS232-like signalling, pretty much each and every manufacturer uses a slightly different take on it in some way or another. There isn't a standard for timing accuracy, either, the limits are when the stop bit slides out of the detection window for that character. I worked extensively on electromechanical Teletypes in the early 70's, and cannot once recall measuring bit rate (rather than baud rate) over multiple characters, because the system relied on re-synchronising at the leading edge of each characters start bit. As long as the bit rate accuracy was sufficient that the stop bit was still seen within the timing window for the last bit of the character, then all was well - the aim when setting them up was to get the centre of the stop bit right on the edge of the detection window, to allow equal drift up and down.
Let's not lose sight of the fact that the Picaxe is an educational system, designed to allow fairly basic programming techniques to be taught and understood by schoolchildren. Some of us routinely push the capability of Picaxe chips way beyond the intentions that Revolution Education have for them, so we should be a little more understanding of some of the limitations. Any flexible, software driven, bit-bashed serial port is going to have some limitations, that's inherent in trying to do something for which the hardware isn't specifically designed.
I've hit the limits of the Picaxe firmware a few times in various projects, but accept that what I've been trying to do is sometimes just too far outside the design envelope for the Picaxe. Perhaps we should be a bit more tolerant of some of these limitations, and not so critical of a small company working on low margins with the primary aim of trying to help educate our kids.
This point seems to be being lost here with esoteric arguments as to who is right or wrong in any particular interpretation of a non-existent "standard". There isn't, as far as I'm aware, an internationally recognised standard for 5V level serial data comms using RS232-like signalling, pretty much each and every manufacturer uses a slightly different take on it in some way or another. There isn't a standard for timing accuracy, either, the limits are when the stop bit slides out of the detection window for that character. I worked extensively on electromechanical Teletypes in the early 70's, and cannot once recall measuring bit rate (rather than baud rate) over multiple characters, because the system relied on re-synchronising at the leading edge of each characters start bit. As long as the bit rate accuracy was sufficient that the stop bit was still seen within the timing window for the last bit of the character, then all was well - the aim when setting them up was to get the centre of the stop bit right on the edge of the detection window, to allow equal drift up and down.
Let's not lose sight of the fact that the Picaxe is an educational system, designed to allow fairly basic programming techniques to be taught and understood by schoolchildren. Some of us routinely push the capability of Picaxe chips way beyond the intentions that Revolution Education have for them, so we should be a little more understanding of some of the limitations. Any flexible, software driven, bit-bashed serial port is going to have some limitations, that's inherent in trying to do something for which the hardware isn't specifically designed.
I've hit the limits of the Picaxe firmware a few times in various projects, but accept that what I've been trying to do is sometimes just too far outside the design envelope for the Picaxe. Perhaps we should be a bit more tolerant of some of these limitations, and not so critical of a small company working on low margins with the primary aim of trying to help educate our kids.