ST25R3911B datasheet(49/129 Pages) STMICROELECTRONICS

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ST25R3911B

Functional overview

During execution of the direct command Measure Phase the transmitter and Phase Detector

are enabled, the Phase Detector output is multiplexed on the input of A/ D converter, which

is set in relative mode. Since the A/D converter range is from 1/6 VSP_A to 5/6 VSP_A the

actual phase detector range is from 30º to 150º. Values below 30º result in FFh, while

values above 150º result in 00h. One LSB of the A/D conversion output represents 0.13% of

carrier frequency period (0.468°). The result of A/D conversion is in case of 90º phase shift

in the middle of range (1000 0000b or 0111 1111b). A value higher than 1000 0000b means

that phase detector output voltage is higher than VSP_A/2, which corresponds to case with

phase shift lower than 90º. In the opposite case, when the phase shift is higher than 90º, the

result of A/D conversion is lower than 0111 1111b. For example, the phase difference of 135º

shown in Figure 7 results in 0.75 VSP_A, result stored in A/D converter is 31d (1Fh).

The phase measurement result can be calculating using the following formulas:

•

0º ≤ φ ≤ 30º: result = 255 (decimal)

•

30º < φ < 150º: angle (in º) = 30 + [(255 - u_angle) / 255) * 120]

•

150º ≤ φ ≤ 180º: result = 0 (decimal)

Duration time: 25 μs max.

This command is accepted in case en (bit 7 of the Operation Control Register) is set and

Xtal oscillator frequency is stable.

Direct command chaining is not possible.

IRQ due to termination of direct command is produced after command execution is

terminated.

Clear RSSI

The receiver automatically clears the RSSI bits in the RSSI Display Register and starts to

measure the RSSI of the received signal when the signal rx_on is asserted. Since the RSSI

bits store peak value (peak-hold type) the variations of the receiver input signal will not be

followed (this may happen in case of long messages or test procedures). The direct

command Clear RSSI clears the RSSI bits in the RSSI Display Register, and the RSSI

measurement is restarted (in case, of course, rx_on is still high).

This command is accepted in case en (bit 7 of the Operation Control Register) is set and

Xtal oscillator frequency is stable.

Direct command chaining is possible.

IRQ due to termination of direct command is not produced.

Transparent Mode

Enters in the Transparent mode. The Transparent mode is entered on the rising edge of

signal /SS and is maintained as long as signal /SS is kept high.

This command is accepted when en (bit 7 of the Operation Control Register) is set and Xtal

oscillator frequency is stable.

Calibrate Capacitive Sensor

This command calibrates the Capacitive Sensor. See Section 1.1.5: Capacitive sensor for

more details.

Duration time: 3 ms max.

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