RF31
3.5. System Timing
The system timing for RX mode is shown in Figure 7. If a small range of frequencies is being used and the
temperature range is fairly constant a calibration may only be needed at the initial power up of the device. The
relevant system timing registers are shown below.
POR
Def.
45h
Function/De
D7
D6
D5
D4
D3
D2
D1
D0
Add R/W
scription
PLL Tune Time
Reserved 1
Calibration
Control
R/W
pllts[4:0]
X
pllt0[2:0]
X
53
R/W
X
X
X
X
X
X
00h
54
xtalstart
half
adccaldo
ne
Vcoca
ldp
R/W
enrcfcal
rccal
vcocal
skipvco
04h
55
The VCO will automatically calibrate at every frequency change or power up. The VCO CAL may also be forced by
setting the vcocal bit. The 32.768 kHz RC oscillator is also automatically calibrated but the calibration may also be
forced. The enrcfcal will enable the RC Fine Calibration which will occur every 30 seconds. The rccal bit will force a
complete calibration of the RC oscillator which will take approximately 2 ms. The PLL T0 time is to allow for bias
settling of the VCO, the default for this should be adequate. The PLL TS time is for the settling time of the PLL,
which has a default setting of 200 μs. This setting should be adequate for most applications but may be reduced if
small frequency jumps are used. For more information on the PLL register configuration options, see ―Register
53h. PLL Tune Time,‖ and ―Register 55h. Calibration Control,‖.
Figure 7. RX Timing
20
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