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SLOS758G – DECEMBER 2011 – REVISED MARCH 2020
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Detailed Description
Copyright © 2011–2020, Texas Instruments Incorporated
6.13.8 Test External RF (RSSI at RX Input With TX Off) (0x19)
This command can be used in active mode when the RF receiver is on but RF output is off. This means
bit B1 = 1 in the Chip Status Control register. The level of RF signal received on the antenna is measured
and reported in the RSSI Levels register (0x0F). The relation between the 3-bit code and the external RF
field strength [A/m] must be determinate by calculation or by experiments for each antenna type, because
the antenna Q and connection to the RF input influence the result.
and
describe the nominal relation between the RF peak-to-peak voltage in the RF_IN1 input and RSSI code,
respectively.
NOTE
If the command is executed immediately after power-up and before any communication with
tag was performed, the command must be preceded by the Enable RX command. The
Check RF commands require full operation, so the receiver must be activated by enable RX
or by a normal tag communication for the Check RF command to work properly.
Table 6-14. Test External RF
RF_IN1 (mV
P
):
40
60
80
100
140
180
300
Decimal Code:
1
2
3
4
5
6
7
Binary Code:
001
010
011
001
101
011
111
6.13.9 Register Preset
After power-up and the EN pin low-to-high transition, the registers are in a default mode, which must be
changed by writing the desired ISO protocol settings to the ISO Control register. The low-level option
registers (0x02 to 0x0B) are automatically configured to the new protocol parameters. After selecting the
protocol, it is possible to change some low-level register contents if needed. However, changing to
another protocol and then back reloads the default settings; therefore, the custom settings must be
reloaded.
The Clo0 and Clo1 bits in the Modulator and SYS_CLK Control register (0x09), which define the
microcontroller frequency available on the SYS_CLK pin, are the only 2 bits in the configuration registers
that are not cleared during protocol selection.
