Radio and RFID reader don't play well together.

I have the RFID_RFC522 RFID reader, and an RFM22B 415 MHz. transceiver sharing the same Nano. These are both SPI devices, and I understand that if the chip select line is high on either one, it should not interfere with communication between the Nano and the other unit. But I find that the radio works only if I don't initialize the RFID unit. And vice versa.

It would seem that if I specifically set the chip select lines of these units so that one is high, and one is low, then one would be active at a time. That also doesn't seem to work. So, two questions.

  1. There is a mode where the RFID reader reports a card present by interrupt: would that mean that it is not using the SPI interface until I go read it?

  2. There is a PICC_HaltA command mentioned in the library: would that completely shut the unit down and free the SPI for the radio?

Unfortunately, the library is not particularly tutorial, so if someone has experience with a similar problem, I'd like to hear solutions.