MC33596FCESLASHR2 datasheet(22/70 Pages) FREESCALE

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MC33596 Data Sheet, Rev. 4

Receive Mode

Freescale Semiconductor

Each time is defined with the associated value found in the RXONOFF register.

•

On time = RON[3:0]

× 512 × Tdigclk (see Table 16; begins after the crystal oscillator has started)

•

Off time = receiver off time = N

× TStrobe + MIN (TStrobe / 2, receiver on time), with N decoded

from ROFF[2:0] (see Table 17)

The strobe oscillator is a relaxation oscillator in which an external capacitor C13 is charged by an internal

current source (see Figure 46). When the threshold is reached, C13 is discharged and the cycle restarts.

The strobe frequency is FStrobe = 1/TStrobe with TStrobe =106 × C13.

In receive mode, setting the STROBE pin to VCCIO at any time forces the circuit on. As VCCIO is above

the oscillator threshold voltage, the condition on which the STROBE pin is set to VCCIO is detected

internally, and the oscillator pulldown circuitry is disabled. This limits the current consumption. After the

STROBE pin is forced to high level, the external driver should pass via a “0” state to discharge the

capacitor before going to high impedance state (otherwise, the on time would last a long time after the

driver release).

When the strobe oscillator is running (i.e., during an off time), forcing the STROBE pin to VGND stops the

strobe clock, and therefore keeps the circuit off.

Figure 14 shows the associated timings.

Figure 14. Receiver On/Off Sequence

11.4 Received Signal Strength Indicator (RSSI)

11.4.1 Module Description

In receive mode, a received signal strength indicator can be activated by setting bit RSSIE.

The input signal is measured at two different points in the receiver chain by two different means, as

follows.

•

At the IF filter output, a progressive compression logarithmic amplifier measures the input signal,

ranging from the sensitivity level up to –50 dBm.

STROBE

Threshold

STROBE

Clock

Digital

Clock

Counter

Receiver

Status

Off

Counter

Crystal Oscillator Startup

Cycling Period

Off

RON

ROFF-1ROFF

tStrobe

STROBE

SET TO VCCIO

RON

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