Download Resistors

[Tricky Dicky]

I am looking to save space on some PCBs by leaving the download socket off where not required for future use.

In effect the the two resistors now simply become a 32K pull-down resistance. Can these be replaced with a 33K or do they need to be that accurate at 32K, OR am I reading page 21 of the manual correctly and it only needs the serial in pin to be pulled down with a 10K.

Ta Richard

 

 

[BrendanP]

I've done as you propose and combined both values in several pcb designs and used a single 33K and it works fine.I dont think the precise value is too critical. Another tip, use 2 decoupling capacitors across the power supply pins, a 10n and 100n.

 

 

[RexLan]

Don't think it needs the resistor ... just pull it low as it is an input. The output can float.

 

[wapo54001]

My understanding is that you can simply connect it directly to ground without a resistor at all. I have done that and my board works well.

 

[Tricky Dicky]

Thanks for the prompt replies.

I must admit I also thought does it even need a resistor at all if all it needs is pulling down low. Its just every manual and even David Lincolns book seem to stress the importance of the resistors even without the download socket.

 

 

[hippy]

You should be okay with Serial In straight to 0V.

The only risk is if there is some 'catastrophic event' which corrupted PICAXE execution which turned the Serial In pin to an output and set it high. This would short a high output to 0V and could potentially destroy the PICAXE.

Such an event could potentially occur when the PICAXE is operated outside its designed operating envelope ( supply voltage too low or high, brownouts, voltage spikes and surges, ESD, etc ), so a pull-down resistor would be the advised route and recommended in a robust design.

In many home or hobby designs it may be considered that the risk of that happening versus the potential damage done is low enough to be discounted.

 

[BeanieBots]

I agree fully with Hippy.
Same goes for pulling reset high, a pull-up resistor should be used but for a hobby application that is very strapped for space, you can get away with a link.