UPD77533 datasheet(31/104 Pages) RENESAS

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Data Sheet S15671EJ4V0DS

µµµµPD77533

6. SYSTEM CONTROL

6.1

FCC Function

The FCC (Frequency Calibration Control) function is used to adjust the accuracy of the local clock (clock signal

input to GPSCLK input pin; 16.384 MHz) using the higher-accuracy reference clock (clock signal input to REFCLK

input pin).

With the

µPD77533, the reference clock used by the FCC function must be supplied during positioning (during

SnapShot) processing. The accuracy of the local clock adjusted by FCC is up to about

±10 ppm.

The following three commands are related to the FCC function.

• “Frequency Calibration Control” (CMD-ID:0x06)

• “FCC Reference Frequency” (CMD-ID:0x02)

• “Doppler Search Range” (CMD-ID:0x57)

6.1.1 Frequency Calibration Control

The Frequency Calibration Control command (CMD-ID: 0x06) is used to set and check whether the FCC function

is enabled or disabled.

For how to set this command, see 16.6 Frequency Calibration Control.

6.1.2 FCC Reference Frequency

The FCC Reference Frequency command (CMD-ID: 0x02) is used to set and check the reference frequency for

the FCC function.

The initial setting for the reference clock is 14.4 MHz.

The value is set as 4-byte data that is the frequency multiplied by 1.024 (therefore the initial value is 0x00E10000

(14.4

× 1.024)).

For details, see 16.2 FCC Reference Frequency.

6.1.3 Doppler Search Range

The Doppler Search Range command (CMD-ID: 0x57) is used to set the Doppler search range (search range of

receive signal frequency). The initial value is 360 Hz (0x168).

The value to be set as the Doppler search range is determined by the local and reference clocks. The calculation

method is shown below.

The minimum value of the Doppler search range parameter (Hz) is calculated as follows.

Doppler search range = 2

× | |DIFr| - |DIFi| | (Hz)

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