are the resistors needed if your not programming

G

geoff07

Senior Member
short answer: yes

long answer: you can't let the pin float so you have to pull the pin voltage down so it doesn't think that there is a signal when there isn't.
 
K

krogerssolar

Senior Member
geoff07 Thanks for that answer might be why im getting this issue why my leds dimly light and not go bright when power is applied to the picaxe
 
G

Grogster

Senior Member
I include the programming circuit in EVERY design, weather you actually use it or not.
In your case, for the sake of two resistors and a PCB header, you can save yourself quite a bit of chip swapping...
 
W

westaust55

Moderator
If you use a single 100 kOhm resistor as the pull down on the Serin pin then the Picaxe will work as required. Additionally if you then use a separate programming circuit such as the axe029 then the Picaxe should still program
 
K

KMoffett

Senior Member
Since Pin 2 is an input-only on the 08M, and the OP wants to program it on another board, can't it be safely grounded, without a pull-down?

Ken
 
premelec

premelec

Senior Member
Maybe future 'special' chips like the 18M2 can have a pulldown internally installed on dedicated input pins so we don't have to ask these questions any more... :)
 
D

Dippy

Moderator
Yes, that's a good idea. As the 18M2 was specially made (!) for Rev-Ed I wonder why it wasn't built-in or , even better, arranged a bit like the WPUs we see in other places...? i.e. a WPD
 
hippy

hippy

Ex-Staff (retired)
An internal pull-down on Serial Input would not necessarily make sense nor work as it would create a potential divider beteen the 22K and the pull-down just as it would if external.

Also it's a lot of effort and cost to solve something with for 99% of people is a non-problem, and for the 1% who want to operate without programming interface is simple enough to make work.

The manuals are very clear on what to do for the download interface to make the PICAXE work, in both cases.
 
hippy

hippy

Ex-Staff (retired)
KMoffett said:
Since Pin 2 is an input-only on the 08M, and the OP wants to program it on another board, can't it be safely grounded, without a pull-down?
Click to expand...
Leg 2 is input only in terms of PICAXE configuration. In silicon it is an input-output connection. The recommendation would be to connect with a pull-down resistor.

Connected directly to 0V there is an increased possibility of damage in adverse circumstances but it is not easy to quantify the possibility of such circumstances or damage occurring.
 
D

Dippy

Moderator
A WPU is a pretty high resistance and a WPD could be too.
The Pot-div effect could be minimised with a swift schoolboy-level calculation.
And, if as I suggested, it was made like a WPU (i.e. settable), then that argument goes out of the window as the user would have the choice.

You say a "lot of effort and cost"; surely a lot of effort and cost went into the unique silicon for the 18M2?
Sometimes a change is a case of "Darling, while you're down there..." :)
I'm being cheeky of course as it's Christmas break.

Anyyywwayy , in seriousness and as we know if would never happen, to have a genuine bit of unique silicon made with a special register would be an expensive thing, for what would be (and I agree here) a rare requirement.

And I certainly agree about the potential risk of direct connections to ground or power.
 
A

Andrew Cowan

Senior Member
As Dippy says, a high value pull down (220K?) would not have a significant pot-divider effect, and it wouldn't be a problem if the pin turned output. Oh well, maybe in future designs.
 
hippy

hippy

Ex-Staff (retired)
I personally think it's all a bit extreme considering all we're talking about is someone forgot to pull-down Serial In when they didn't use the download interface.

Possibly Microchip could add an on-chip nuclear-pile for when someone forgets to connect a power supply, or a voltage regulator on-board for when someone forgets the chip blows up at some voltage, be designed to withstand reverse voltage connection, or include series resistors in I/O for when someone forgets a current limiting resistor for a LED ?

I'm not saying they shouldn't or those or WPD are to be rejected out of hand - and I actually think they're all good ideas in themselves - but unless you are heading into Microchip HQ with buckets of gold coins in tow the only thing one can do is offer a suggestion and see if they believe it has appeal and rationale and implement it. Sometimes they do take suggestions on-board; the ability to switch polarity on the on-chip UART was something I and others had long asked for which finally arrived.
 
D

Dippy

Moderator
Oh yes, it could be ridiculously expensive.

And, I would assume, that modules and peripherals on a PIC are designed around compiled/ASM code where it is easier to allow for things.
Making hardware optimised for a firmware/loader would probably make PICAXE as expensive as a Stamp :)

But it's fun to muse (a good rock band by the way).

And I was told yesterday about a car manufacturer who spent 10's of thousands of quiddlies rejigging a PCB to lose 2 resistors - so there is mileage when a Micro Manuf puts more on the chip ;)
e.g. some of the Freescale offerings.
 
F

fritz42_male

Senior Member
Might it be worth them doing an SMT board with the resistors built in? Would fulfill the smallness requirement. You could have the headers in place for programming as well.

Edit - Just found the 08M SMT board - DUH!!!
 
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hippy

hippy

Ex-Staff (retired)
MAX232 etc have "PC interfacing" built in so no external pull-up or pull-down needed. The signal to PICAXE Input is hard high or low, never floating, so also no pull-up or pull-down needed.

Note that MAX232 etc use idle-high polarity interfacing to the PICAXE so there needs to be an inversion added if a MAX232 is connected to the download Serial In and Out.
 
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