08M reset?

[CWells]

I'm working on a project with two 8M's connected to another uC. I've found that the 8M's are getting powered up through the serial line, which is a problem because I can't reset them now, and they spend all their time hanging on a serin statement.

1. Is there a direct way to reset an 8M getting power in this way? Can I choke off the incoming power somehow, such as with a resistor? I've already got a 1K to the input pin on the other uC.

2. Is there a way to wait for a serial signal while still being able to perform other functions?


Note: There are no coding problems.

 

[Dippy]

Sounds like the parasitic power issue. Pain.

Sounds like the other uC idles high on it's Serout pin TO your PICAXE Serin pin.
Unless there are any other connections not mentioned? e.g. a Status pin.
(If there are, then a schematic would help hugely).


"Can I choke off the incoming power somehow, such as with a resistor? "
- are you talking about the serial from mystery uC nipping up your PICAXE serial pin here?
If so, yes, try it. Try a 10K , 22K or anything in your drawer above 10K.
It won't blow up .... be brave.
The worst that will happen is that is simply won't work.
Go on... dare you

Do you have any control over the code from the other uC?
Is it connected to the uArt of another PIC?
If its a soft serial and you are coding other chip then you can control the level until PICAXE has 'settled down'.

Or could you control power-up of other uC from PICAXE?
So that PICAXE can settle down before other uC powers up.
(Just suggestions as I haven't got a clue about the mystery uC)

 

[pha555]

The -08M is great. Inexpensive, and low entry curve.

But, in an application such as this, it just seems it might be worth the extra effort of a PIC16F688 with an external reset and an on-board UART.

P H Anderson

 

[hippy]

Would I be right in assuming the 08M's are normally continuously powered and it's just that they can't be power-cycled / reset to enable the download of a new program ?

If so, one option is to link the uC serial in at the PICAXE pin side of the 1K ( ie, on the PICAXE pin ) to 0V. Make the link, power cycle the PICAXE and download should happen.

That the uC output goes through 1K and to 0V shouldn't cause the uC any problem, unless it cannot handle 5mA sink. It would be possible to increase the R, even up to 10K or more perhaps if worried about that aspect.

If you can find a two-pole, three-way switch you can wire that for debugging as follows -

Download - Link shorted, power connected
Off - Link shorted, power disconnected
Run - Link open, power connected

You may prefer a different switch order, but that given can save the mistake of switching from Run to Download and subsequent head scratching as it doesn't actually power-cyle the device.

You can either switch the 08M as a pair, or split the uC serial through separate 1K and switch each individually.

 

[Andrew Cowan]

The -08M is great. Inexpensive, and low entry curve.

But, in an application such as this, it just seems it might be worth the extra effort of a PIC16F688 with an external reset and an on-board UART.

P H Anderson

16F688? The PICAXE 18X is a 16F88 - otherwise you need raw PICs.

The 18X is now superseded by the 20X2 (pretty much).

A

 

[pha555]

Yes, the raw PIC16F688. Not a PICAXE.

The PICAXE is terrific. But, I am saying there are types of problems where the PICAXE just doesn't appear to be the best answer and my thought is that this is one of them. Admittedly, there is a steep learning curve with the PIC, but not insurmountable for many in this forum.

Another example is interfacing with multiple PICAXE's using serial. Given enough time ..., but perhaps an Arduino Mega with four UARTs might be a better approach which saves a lot of development time.

My intent is not to send folks away as I am a firm believer, but there are few absolute truths.

P H Anderson

 

[CWells]

Maybe I should upgrade to a 18X? I'll learn PIC programming if necessary, but I'm already trying to learn to use my Arduino & a Propeller chip...trying to keep my homework to a minimum. I've already got a couple of 18X's handy, and they're cheap, and I could use an interrupt for the serial input, and a reset line...

 

[tomleijen]

1:
Could you possibly invert the serial signal using a logic gate such as a 7404? (NOT gate with six gates per chip - http://en.wikipedia.org/wiki/Inverter_(logic_gate) )
That way it will idle at zero and the picaxe shouldn't be powered.

Then change the baudmode to read an inverted signal?

From picaxe manual

Baudmode is a variable/constant (0-7) which specifies the mode:
Txxx give a true output (idle high)
Nxxx give an inverted output (idle low)

I know the NOT gate will not produce a true serial command, but the picaxe shouldn't need this as it can't read levels below 0v and above 5v (power supply) anyway.

2:
I am looking for a solution to this too, I am thinking along the lines of using an interrupt, but I have no experience with this.

 

[moxhamj]

Re parasitic powering I've gone for picaxe<=>max232<=>wire<=>max232<=>other picaxe.

Two extra chips and 8 capacitors.

Or, as you say, try to fit it all into an 18X instead. Or 20X2.