Download circuit obsolete?
- Thread starter premelec
- Start date
Have you thought about what you would replace it with ?
There are some of the high end PICs that can talk USB, but the PICs used for PICAXEs only talk serial.
The other 'popular' micros out there that appear to be USB capable use a seperate chip on the board to translate the USB to serial.
So if you want to changed the whole concept of PICAXEs, supplying them on expensive PCBs with all the USB support circuitry included, then I guess you could achieve a USB capable PICAXE board.
Last edited:
What is obsolete (in the 10/2013 manual) is the download circuit that was designed to cope with serial voltages to the RS-232 standard i.e. out of the +5/0 range. It was obsoleted by the provision of the USB download cable. Picaxe does have a USB interface - it is in the cable plug. That keeps the circuits simple (=inexpensive). What could be simpler than three wires and single program statements to access the link? You can always dedicate a cable to an application if it helps. The alternative would be having a proprietary chip from ftdi on every board. Good for ftdi's revenue. but not for much else.
We recommend using the AXE027 USB to jack plug cable for programming PICAXE chips.
The older AXE026 RS232 9-way to jack plug and AXE025 RS232 9-way to 3-way 0.1 header cables are no longer recommended and their use is considered obsolete.
Likewise the enhanced download circuit is not required when using an AXE027 cable and is thus also rendered obsolete.
It would be possible to move the USB-to-serial interface onto the PICAXE development board rather than using a cable but this would increase costs and would make it more difficult to route serial other than the programming pins. We would still need to provide a means of programming standalone PICAXE chips.
Using a PICmicro with USB support looks appealing but is not as practical as it first appears. When the PICAXE is dedicated to a timing task it cannot service USB updates which come from a host every few milliseconds so may end up being treated as disconnected by the PC, rendered inactive until re-plugged in or reset. That could make for a poor user experience and would limit debugging options. There are also only a limited range of devices which support USB which are not always in home user and hobbyist friendly formats.
The older AXE026 RS232 9-way to jack plug and AXE025 RS232 9-way to 3-way 0.1 header cables are no longer recommended and their use is considered obsolete.
Likewise the enhanced download circuit is not required when using an AXE027 cable and is thus also rendered obsolete.
It would be possible to move the USB-to-serial interface onto the PICAXE development board rather than using a cable but this would increase costs and would make it more difficult to route serial other than the programming pins. We would still need to provide a means of programming standalone PICAXE chips.
Using a PICmicro with USB support looks appealing but is not as practical as it first appears. When the PICAXE is dedicated to a timing task it cannot service USB updates which come from a host every few milliseconds so may end up being treated as disconnected by the PC, rendered inactive until re-plugged in or reset. That could make for a poor user experience and would limit debugging options. There are also only a limited range of devices which support USB which are not always in home user and hobbyist friendly formats.
That may make it more convienent for a very limited number of users, but far more complicated for most.
Think about it, which is supplying power, the 'simpler' plug with more connections (?) or the project itself, and what happens if you get them confused, is that also 'simpler' ?
Most of us who are faithful to the Picaxe brand have the old RS232 DB9 to stereo cable and do not wish to part with AUS$24 for the AXE027 cable. To me it looks like a bit of drip-pricing that beginners find to their horror they must spend that kind of money to get the proto board to work. The beauty of the Picaxe is that it is still possible to talk to the PIC cheaply in a non-USB way. The problem is though, a lot of modern computers have done away with RS232.
While I do not particularly care for the stereo connector, I like mini/micro USB connectors even less. I have quite a few devices with mini/micro USB connectors and after being used a while sometimes the connector must be tweaked/jiggled to work. IMO they just don't hold up very well. The stereo connector works well in an educational environment when the socket is soldered onto a project board. However on a breadboard it can be a real pain. I have several AXE027 cables, one is unmodified and used with project boards that have the stereo socket. The other has the stereo plug removed and a three pin header socket installed. This cable is used for manufactured boards and breadboards where a 3 pin header is used to save board space.
The recommended download circuit of a 22K current limit resistor and 10K pull down resistor seems to be a throw back to the days of RS232 signal levels that can be as high as +15/-15V. But, with a 5V supply and an AX027 which has 5V I/0 levels, the 22K resistor is really not needed at all. However, many of us operate the Picaxe at lower voltages, such as 3.3V or even lower. In this case, for the internal clamp diodes to work effectively it is necessary to use a current limit resistor. Any value from 330R to to 22K will work fine and make the Picaxe "5V tolerant". When using an AXE027, and where there will never be RS232 voltage levels, I generally use a 1K resistor to limit the current to about 5 ma.
I would however, like to see a cable made available the brings out the USB 5V, that would allow powering a breadboard or Project board from the USB port. For now I just make my own if the need arises.
NOTE: If using and RS232 connection/cable it is important to use the 22k Resistor, which in effect, limits the current into the serin pin to about 600ua.
Last edited:
The AXE027 is resonably priced in my view, it works and is supported.
If it were cut in price, which items should have thier price increased to compensate ?
To those that are 'horrified' by the price of the AXE027, you can tkae your pick of dodgy USB to serial leads on eBay, some might even have geniune FTDI chips in them ..............
or add a com port PCI card to your machine - you may even get to ports.
I personally have an old school d-sub to stereo lead and a home made d-sub to stereo connected to a 8 year old USB to serial adaptor (as far as I can tell identical to USB010). Both connected to the same machine, handy for multi chip project, or receiving signals from the FPU once the signals have been inverted.
I personally have an old school d-sub to stereo lead and a home made d-sub to stereo connected to a 8 year old USB to serial adaptor (as far as I can tell identical to USB010). Both connected to the same machine, handy for multi chip project, or receiving signals from the FPU once the signals have been inverted.