User's Manual

TRF7970A
www.ti.com SLOS743K –AUGUST 2011–REVISED APRIL 2014
Table 6-7. Coding of the ISO Control Register For RFID Mode (B5 = 0) (continued)
Iso_4 Iso_3 Iso_2 Iso_1 Iso_0 Protocol Remarks
0 1 0 1 0 ISO14443 A high bit rate 424 kbps
0 1 0 1 1 ISO14443 A high bit rate 848 kbps
0 1 1 0 0 ISO14443B, bit rate 106 kbps
RX bit rate when TX rate
0 1 1 0 1 ISO14443 B high bit rate 212 kbps different from RX rate (see
register 0x03)
0 1 1 1 0 ISO14443 B high bit rate 424 kbps
0 1 1 1 1 ISO14443 B high bit rate 848 kbps
1 0 0 1 1 Reserved
1 0 1 0 0 Reserved
1 1 0 1 0 FeliCa 212 kbps
1 1 0 1 1 FeliCa 424 kbps
Table 6-8. Coding of the ISO Control Register For NFC
Mode (B5 = 1, B2 = 0) or Card Emulation (B5 = 1,
B2 = 1)
Card Emulation
Iso_1 Iso_0 NFC (B5 = 1, B2 = 0)
(B5 = 1, B2 = 1)
0 0 N/A ISO14443A
0 1 106 kbps ISO14443B
1 0 212 kbps N/A
1 1 424 kbps N/A
6.5.1 Received Signal Strength Indicator (RSSI)
The TRF7970A incorporates in total three independent RSSI building blocks: Internal Main RSSI, Internal
Auxiliary RSSI, and External RSSI. The internal RSSI blocks are measuring the amplitude of the
subcarrier signal; the External RSSI block measures the amplitude of the RF carrier signal at the receiver
input.
6.5.1.1 Internal RSSI – Main and Auxiliary Receivers
Each receiver path has its own RSSI block to measure the envelope of the demodulated RF signal
(subcarrier). Internal Main RSSI and Internal Auxiliary RSSI are identical however connected to different
RF input pins. The Internal RSSI is intended for diagnostic purposes to set the correct RX path conditions.
The Internal RSSI values can be used to adjust the RX gain settings or decide which RX path (Main or
Auxiliary) provides the greater amplitude and hence to decide if the MUX may need to be reprogrammed
to swap the RX input signal. The measuring system latches the peak value, so the RSSI level can be read
after the end of each receive packet. The RSSI register values are reset with every transmission (TX) by
the reader. This ensures an updated RSSI measurement for each new tag response.
The Internal RSSI has 7 steps (3 bit) with a typical increment of approximately 4 dB. The operating range
is between 600 mV
PP
and 4.2 V
PP
with a typical step size of approximately 600 mV. Both Internal Main
and Internal Auxiliary RSSI values are stored in the RSSI Levels and Oscillator Status register (0x0F). The
nominal relationship between the input RF peak level and the RSSI value is shown in Figure 6-5.
Copyright © 2011–2014, Texas Instruments Incorporated Detailed Description 25
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