[OpenTRV-dev] SMD version of ATmega328P

[Kevin Wood]

Hi Damon,

You're driving the MISO, MOSI, SCK and RESET lines to achieve in system 
programming. As long as you don't exceed the voltage ratings of the 
RFM23B's inputs (i.e. try to program the board at 5V) it shouldn't be 
damaged, and as long as you don't assert the nSEL input to the RFM, it 
won't be active, so will place a high impedance at those pins and 
shouldn't corrupt the programming process.

I don't see it presenting any problems but the proof of the pudding...

I think the only thing that can scupper it is if the nSEL pin gets 
asserted by the programming process. Will have to wade through the data 
sheet to see if there are any guarantees there, but it would be sensible 
if all the pins floated high during the ISP process.

Kevin

On 24/07/14 17:31, Damon Hart-Davis wrote:
> Hi,
>
> We’re starting production engineering work in earnest very soon, and we’re going to need to support in-circuit programming to use SMD.
>
> I believe the standard way to do this involves driving the SPI bus as for loading a bootloader.
>
> I am concerned that this cannot be done without damaging the RFM23B attached to the SPI bus, or am I wrong about that?  What gotchas don’t I even know about yet?
>
> Thanks
>
> Damon
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