PIC12F635ESS datasheet(109/234 Pages) MICROCHIP

109 / 234 page

DS41232D-page 107

PIC12F635/PIC16F636/639

11.20 Soft Reset

The AFE issues a Soft Reset in the following events:

After Power-on Reset (POR),

After Inactivity timer time-out,

If an “Abort” occurs,

After receiving SPI Soft Reset command.

The “Abort” occurs if there is no positive signal

detected at the end of the AGC stabilization period

(TAGC). The Soft Reset initializes internal circuits and

brings the AFE into a low current Standby mode

operation. The internal circuits that are initialized by the

Soft Reset include:

• Output Enable Filter

•AGC circuits

• Demodulator

• 32 kHz Internal Oscillator

The Soft Reset has no effect on the Configuration register

setup, except for some of the AFE Status Register 7 bits.

(Register 11-8).

The circuit initialization takes one internal clock cycle

(1/32 kHz = 31.25

μs). During the initialization, the

modulation

transistors

between

each

input

and

LCCOM pins are turned-on to discharge any inter-

nal/external parasitic charges. The modulation transis-

tors are turned-off immediately after the initialization

time.

The Soft Reset is executed in Active mode only. It is not

valid in Standby mode.

11.21 Minimum Modulation Depth

Requirement for Input Signal

The AFE demodulates the modulated input signal if the

modulation depth of the input signal is greater than the

minimum requirement that is programmed in the AFE

Configuration Register 5 (Register 11-6). Figure 11-7

shows the definition of the modulation depth and

examples. MODMIN<6:5> of the Configuration Register

5 offer four options. They are 75%, 50%, 25% and 12%,

with a default setting of 50%.

The purpose of this feature is to enhance the

demodulation integrity of the input signal. The 12%

setting is the best choice for the input signal with weak

modulation depth, which is typically observed near the

high-voltage base station antenna and also at

far-distance from the base station antenna. It gives the

best demodulation sensitivity, but is very susceptible to

noise spikes that can result in a bit detection error. The

75% setting can reduce the bit errors caused by noise,

but gives the least demodulation sensitivity. See

Table 11-3 for minimum modulation depth requirement

settings.

TABLE 11-3:

SETTING FOR MINIMUM

MODULATION DEPTH

REQUIREMENT

MODMIN Bits

(Config. Register 5)

Modulation Depth

Bit 6

Bit 5

50% (default)

75%

25%

12%

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