1. Using TRF7970A in SPI w/o SS mode, then in Direct Mode 1
Texas Instruments
Embedded RF
12/15/2011

2. Procedure Overview
The Procedure for entering DM1 in SPI w/o SS is the following:
Write Register 0x00 with 0x21 (Enable TX/RX, see slide 4)
Write Register 0x01 with 0x48 (Select DM1, see slide 4)
Clear IRQ register 0xC0 (see slide 4)
Send Direct Command 17 (Enable decoder, see slide 5)
Write Register 0x00 with 0x61 with 8 extra clock pulses and no stop condition (this puts the part in DM1 and 8 extra clock pulses are needed because there is no stop condition in the communication, see slide 6)
Transmit data using the MOD pin (Green trace)
Receive response in DM1 on I/O_5 (Data Clock in DM1) and I/O_6 (Bit Data in DM1, see slide 7, Note: I/O_6 is labeled MISO)

3. MOD pin
RF field

4. Write Register 0x00 with 0x21 Write Register 0x01 with 0x48

5. Clear IRQ register 0xC0 Send Direct Command 17 (Enable decoder)

6. Write Register 0x00 with 0x61 with 8 extra clock pulses and no stop condition (this puts the part in DM1)

7. Transmit data using the MOD pin
Receive response in DM1
MOD pin