I have a project that I'm using to learn where I have multiple devices connected to an atmega328p over SPI. I started with the Arduino platform and got everything working individually there and am now cutting back to breadboarding the components that I need and getting everything working at the same time.
My problem is that I'm using an ISP header to program the 328p in circuit and I think I need to set the slave select of the other SPI devices to active low and I don't know how to do that. What I'm seeing is that programming the 328p via ISP fails unless I remove all other SPI wiring.
I think I should be "tieing" the SS of the slave devices to 3.3v via a 10k ohm resistor, but then how do I get the pin to go low via a pin on the 328p? I'm currently doing that via a physical button on the 328p's reset pin but I think I want to do this via one of the digital pins. I think I could use a transistor to drain the SS on the slave to ground. Is this right? What would the circuit be?