SPI, one CS pin, 2 devices, PNP transistor?

Other Hardware General Electronics
1

hi,

I'm thinking of using one CS (chip select/slave select) pin to control two devices on the SPI bus. One of the devices' CS pin will be connected to the Arduino CS pin through a PNP transistor, the other device directly. Are there any known issues with such a setup?

thanks!

SPI-2devices-1CSpin-PNP.jpg

2

Other than your apparent goal of having one or the other being active ALL the time?
When the arduino pin is low, device 1 will be driven high and device 2 low.
When the arduino pin is high, device 1 will be floating, and device 2 high. At least put a pulldown resistor on the pin so it can go low.

3

CrossRoads:
Other than your apparent goal of having one or the other being active ALL the time?

They will toggle. Device 1 = a few PISO shift registers, device 2 = a few SIPO registers.

When the arduino pin is high, device 1 will be floating, and device 2 high. At least put a pulldown resistor on the pin so it can go low.

yep, forgot about that.

thanks!

4

Some SPI devices have actions that happen when CS is activated (whether or not
any bits are shifted through). I'd check the datasheets or experiment to make sure
there aren't unintended consquences.