4.3.6 Fractional-N PLL Register Overview

The PLL uses the following registers. The application software must not change the RF front-end register (see the following table). The firmware uses them to control the start-up, power-down and calibration of the fractional-N PLL.

Table 4-1. RF Front-end Registers used by Firmware

Register

Function

FESR.PLCK

PLL locked

FEEN1.PLSP1

PLL speed-up

FEEN1.PLCAL

PLL Calibration mode

FEEN1.PLEN

PLL enable

FEEN2.PLPEN

PLL post enable

FECR.PLCKG

PLL lock detect gate

FEVCT.FEVCT[3:0]

RF front-end VCO tuning register

The RF front-end values are transferred from the factory-locked EEPROM to the RF front-end by firmware before using the PLL (see the following table).

Table 4-2. RF Front-end Registers for Factory Locked Calibration

Register

Function

FEBT.RTN2[1:0]

Resistor tuning

FEBT.CTN2[1:0]

Capacitor tuning

FETN4.CTN4[3:0]

Capacitor tuning

FETN4.RTN4[3:0]

Resistor tuning

FEVCO.VCOB[3:0]

VCO bias 4-bit value(1)

FEVCO.CPCC[3:0]

Charge pump current control(1)
Note:
  1. For this register information, use a calibration value from the factory-locked EEPROM and an application-specific value from the EEPROM settings. The register information must be copied to the RF front-end registers before using the PLL.

The RF front-end registers from RF Front-end Registers used by Firmware are changed due to application-specific settings coming from the EEPROM. See RF Front-end Registers used by Firmware in the Fractional-N PLL Register Overview from Related Links. Use the configuration tool must to calculate these EEPROM settings. In the configuration tool, modify the FFREQ settings to compensate both the initial XTO and the XTAL frequency tolerances. Consider the exact frequency steps of the PLL (fXTO/218 = 92.7 Hz in Low-band frequency range and fXTO/217 = 185.43 Hz in High-band when using a 24.3 MHz crystal).

Table 4-3. RF Front-end Registers Used for Application Settings

Register

Function

FEMS.M[3:0]

Main counter

FEMS.S[3:0]

Swallow counter

FECR.S4N3

Select 433MHz/315MHz band

FECR.LBNHB

Select Low-/High-band

FEVCO.VCOB[3:0]

VCO bias (1)

FEVCO.CPCC[3:0]

Charge pump current control (1)

Note:
  1. For this register information, use a calibration value from the factory-locked EEPROM and an application-specific value from the EEPROM settings. The register information must be copied to the RF front-end registers before using the PLL.