Picaxe newbie - It won't download!

[jarin42]

I recently bought a Picaxe 28X chip to experiment with, and built my own download circuit on a breadboard, like the one in the 28 section of the axe001_pcb file, but with the exeption of the darlington chip. I definately built it right, but it doesn't download. I am probably being very stupid, but surely the RS232 line level, +-10v, needs conversion to the +5-0v level of the picaxe chip?
All help gratefully recieved.

 

[Technical]

but surely the RS232 line level, +-10v, needs conversion to the +5-0v level of the picaxe chip?

Please see the minimum operating circuit in part 1 of the manual. The 10k/22k does the voltage conversion required.

 

[Wrenow]

Also, read the manual on troubleshooting the connection using the software. When building my own circuit, I personally found about all of the ways you can hook 5 wires to 3 positions wrong, until I read the troubleshooting section, then had it sorted in short order.

Wreno

 

[jarin42]

Thanks for the replies and sorry for not getting back sooner. I am pretty sure it is all connected right, but is it possible I damaged the chip by connecting it wrongly before? Also, I don't know if it might never have been programmed with the PICAXE code- it hasn't got a sticker or anything.

 

[Dippy]

"..by connecting it wrongly before?"
Aha, the truth is coming out
Depends what you mean by wrongly. What did you do?

"...it hasn't got a sticker or anything" - where did you buy it? From Rev-Ed? If so, it will be pre-programmed PICAXE.
If you bought it from a bloke down the pub then who knows.

Unless you've broken it there is a 99% chance it's your wiring or power supply. We see this quite often and it usually ends up as "oh oops".
So, check batteries or psu, check pullup res from reset to 5V (or whatever your Vsupply is).
Treble check your download circuit and if necessary check you've got the right val res with a multimeter as some people can't read colour codes - or a duff res , yes it's happened to me. Quadruple check your serial connections to make sure they're not aaf.
"pretty sure" ain't good enough.

I take it you have nothing else electrically noisy (or overloaing) connected to PICAXE or supply?

 

[BeanieBots]

They are pretty tough little things and will cope with quite a lot of abuse, so unless you connected power the wrong way or stuffed 12v into it, then the odds are, it is OK. (even wrong polarity with batteries will often survive).

They don't have any indication of being a PICAXE. As long as it was purchased as PICAXE and not PIC, then it will have the required bootloader firmware.
Double check the two resistors for serin. (NOT a voltage divider)
Check reset is held high.
Check resonator connections (and frequency).

Have you tried a firmware check? Even when software fails to load, that often still works OK.

 

[jarin42]

I have checked everything again, including all serial cable connections- all are right. Come to think of it, I did forget to put the two resistors on to start with... I'll have to come to the conclusion that it's broken.

 

[inglewoodpete]

I think you have found the answer. Without the 22k/10k resistors, the 10 to 12v from the PC's serial port has probably zapped the PICAXE's 'serial in' input.

The 22k/10k resistors perform 2 essential roles: (1) holding the serial in pin low when the download lead is disconnected and (2) limiting the current into the serial in pin when a 10 to 12v serial signal is received from the PC.