Texas Instruments TRF7970A Instruction Manual page 68

TRF7970A
SLOS743K – AUGUST 2011 – REVISED APRIL 2014
6.14.3.3.3 RSSI Levels and Oscillator Status Register (0x0F)
Table 6-47. RSSI Levels and Oscillator Status Register (0x0F)
Function: Displays the signal strength on both reception channels and RF amplitude during RF-off state. The RSSI values are valid from
reception start till start of next transmission.
Bit Name
B7 Unused
Crystal oscillator stable
B6 osc_ok
indicator
MSB RSSI value of auxiliary
B5 rssi_x2
RX (RX_IN2)
B4 rssi_x1 Auxiliary channel RSSI
MSB RSSI value of auxiliary at RX_IN2.
B3 rssi_x0
RX (RX_IN2)
MSB RSSI value of main
B2 rssi_2
RX (RX_IN1)
B1 rssi_1 Main channel RSSI
LSB RSSI value of main RX
B0 rssi_0
(RX_IN1)
RSSI measurement block is measuring the demodulated envelope signal (except in case of direct
command for RF amplitude measurement described later in direct commands section). The measuring
system is latching the peak value, so the RSSI level can be read after the end of receive packet. The
RSSI value is reset during next transmit action of the reader, so the new tag response level can be
measured. The RSSI levels calculated to the RF_IN1 and RF_IN2 are presented in
Section 6.5.1.2. The RSSI has 7 steps (3 bits) with 4-dB increment. The input level is the peak to peak
modulation level of RF signal measured on one side envelope (positive or negative).
6.14.3.3.4 Special Functions Register (0x10)
Function: User configurable options for ISO14443A specific operations
Bit Name
B7 Reserved
B6 Reserved
Disables parity checking for
B5 par43
ISO14443A
0 = 18.88 µs
B4 next_slot_37us
1 = 37.77 µs
Bit stream transmit for
B3 Sp_dir_mode
MIFARE at 106 kbps
0 = normal receive
B2 4_bit_RX
1 = 4-bit receive
0 = anticollision framing
(0x93, 0x95, 0x97)
B1 14_anticoll
1 = normal framing (no
broken bytes)
0 = 7 subcarrier pulses
B0 col_7_6
1 = 6 subcarrier pulses
68 Detailed Description
Function
13.56-MHz frequency stable (≈200 µs)
Auxiliary channel is by default RX_IN2. The input can be swapped by B3 = 1
(Chip State Control register 0x00). If "swapped", the Auxiliary channel is
connected to RX_IN1 and, hence, the Auxiliary RSSI represents the signal level
Active channel is default and can be set with option bit B3 = 0 of chip state
control register 0x00.
Table 6-48. Special Functions Register (0x10)
Function
Reserved
Reserved
Sets the time grid for next slot command in ISO15693
Enables direct mode for transmitting ISO14443A data, bypassing the FIFO and
feeding the data bit stream directly onto the encoder.
Enable 4-bit replay for example, ACK, NACK used by some cards; for example,
MIFARE Ultralight
Disable anticollision frames for 14443A (this bit should be set to 1 after
anticollision is finished)
Selects the number of subcarrier pulses that trigger collision error in the
14443A - 106 kbps
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Section 6.5.1.1 and