AXE026 Question

[magusjonny42]

Im just getting used to programming PICs with my JDM programmer and I find this nifty PICAXE site. Very cool stuff but im stumped on something and need an answer to my query. How does PICAXE get away with programming their modified pics with only a 3 conductor audio jack?

Now from what I could find in PICAXE manual (picaxe_manual1.pdf) this is my initial hypothesis on the pinout conversion from the auido jack to general ICSP.

Stereo Audio Jack/3 conductor TRS
A (Sleeve) Serial Out = Data
B (Ring) Serial In = Clock
C (Tip) 0v = Ground

So were are VDD and VPP?

Also what is the corresponding pinout from the audio jack to the DB5 on the AXE026?

If there is already a thread with all this answered I am more then willing to read it. Just point me in the right direction and I will go consume.

 

[westaust55]

Vdd comes from the PICAXE board power supply, be that three AA cells for 4.5V or a voltage regulator for typically 5V

The PIACXE chips are pre programmed with a boot loader (another very recent thread on this you can look for) and a BASIC tokenised program interpreter.
(Edit) see this link: http://www.picaxeforum.co.uk/showthread.php?t=12874

This method makes programming of the PIC chip easier and there is no need for a higher Vpp voltage as no fuses etc are being reprogrammed.
The method of using a bootloader is not restricted to the PICAXE chips.


The AXE026 cable datasheet is normally here:
http://www.rev-ed.co.uk/docs/AXE026.pdf
but while there are currently links to this document on the Rev Ed website, is is missing from the All Datasheets list and the page cannot be found.

 

[BeanieBots]

Welcome to the forum.

It's the simplicity of programming which makes the PICAXE system so special.
Just three wires between PC and PIC. Just two resistors at the PIC. No need for a programmer. In circuit programming.

Note however, that you cannot program a totally blank PIC in the same way.

 

[Dippy]

And also don't directly compare PICAXE programming with PIC+'normal' bootloader.

You'll already know that PIC hardware programming connections are Vdd, Vpp,PGData,PGClock,Gnd and a bootloaded PIC is Vdd(opt),TX,Rx,Gnd via inverter/MAX232.

But a PICAXE uses a unique loader scheme and you won't be able to load hex using a microcode loader. You must use Rev-Ed Programme Editor.

 

[hippy]

How does PICAXE get away with programming their modified pics with only a 3 conductor audio jack?

It uses standard serial comms so, 0V, TX and RX and avoids the necessity of requiring a MAX232 serial interface that other bootloader products may need. The Bootloader part of the pre-programmed firmware reads the serial and moves the programming data into the chip.

No ICSP used at all, and the downloaded program is compiled to a tokenised form rather than raw PIC instructions. This means all PICAXE's have to support self-programming for Flash memory, or the downloaded program is held in on-chip Data Eeprom ( hence the 256 byte program limit on the 08M etc ).

Also what is the corresponding pinout from the audio jack to the DB5 on the AXE026?

I cannot recall which datasheet / PICAXE Manual the diagram is in but it's ...

3.5mm tip ( 0V ) to DB9 pin 5 ( 0V )
3.5mm ring ( Serial In to PICAXE ) to DB9 pin 3 ( TX from PC )
3.5mm sleeve ( Serial Out from PICAXE ) to DB9 pin 2 ( RX to PC )

We recommend the use of the AXE027 USB-to-serial cable.

 

[MartinM57]

How does PICAXE get away with programming their modified pics with only a 3 conductor audio jack?

Just to be clear - it doesn't.

You also need to supply your own Vdd and Vpp (Vss, 0v, ground etc)...and the programming circuit, which in it's minimalist state is two resistors.