Programming two ATMEGA328's on same SPI bus feasibility

Hey all,

I wanted to post a quick question about flashing ATMEGA328’s over ICSP.

I’m making an edge card that has two ATMEGA328’s on it, and I broke out the mutual SPI lines (MOSI, MISO, SCLK) and the individual RESET lines (RESET for one, and for the other) for a total of 5 signals coming out of the edge card. This is in addition to 5V & GND. Basically the ICSP pinouts but on my edge card.

I am then trying to be able to program each of them from a special jig that has the edge card receptacle.

My question that I’m not totally sure on is if I’ll have any problem flashing these two when the SPI bus is joined. That is, I’ll only ever be programming one at a time (by only pulling one reset low when programming), but I’m worried having a joint SPI bus can be problematic.

That is, when programming one controller, the other controller is inherently powered on – and I’m wondering if somehow it’ll be sourcing it’s own clock line on SCLK, or somehow responding to data on MISO, or outputting on MOSI.

To be clear, I won’t be using SPI for anything itself. The controllers will use the broken out SPI bus for programming, but never use SPI in their actual functionality.

My inclination is to say no, but I wanted to be sure I’d be able to program them both on the combined bus.