4432-T-B1 B 915【PDF 27/47 页】KIT DEV TEST EZRADIOPRO SI4432

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Sheet目录49

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Si4430/31/32-B1

Rev 1.1

3.5.2. Easy Frequency Programming for FHSS

While Registers 73h77h may be used to program the carrier frequency of the Si4430/31/32, it is often easier to

think in terms of channels or channel numbers rather than an absolute frequency value in Hz. Also, there may

be some timing-critical applications (such as for Frequency Hopping Systems) in which it is desirable to change

frequency by programming a single register. Once the channel step size is set, the frequency may be changed by

a single register corresponding to the channel number. A nominal frequency is first set using Registers 73h77h,

as described above. Registers 79h and 7Ah are then used to set a channel step size and channel number, relative

to the nominal setting. The Frequency Hopping Step Size (fhs[7:0]) is set in increments of 10 kHz with a maximum

channel step size of 2.56 MHz. The Frequency Hopping Channel Select Register then selects channels based on

multiples of the step size.

For example, if the nominal frequency is set to 900 MHz using Registers 73h77h, the channel step size is set to

1 MHz using "Register 7Ah. Frequency Hopping Step Size," and "Register 79h. Frequency Hopping Channel

Select" is set to 5d, the resulting carrier frequency would be 905 MHz. Once the nominal frequency and channel

step size are programmed in the registers, it is only necessary to program the fhch[7:0] register in order to change

the frequency.

3.5.3. Automatic State Transition for Frequency Change

If registers 79h or 7Ah are changed in either TX or mode, the state machine will automatically transition the chip

back to TUNE, change the frequency, and automatically go back to either TX or RX. This feature is useful to reduce

the number of SPI commands required in a Frequency Hopping System. This in turn reduces microcontroller

activity, reducing current consumption. The exception to this is during TX FIFO mode. If a frequency change is

initiated during a TX packet, then the part will complete the current TX packet and will only change the frequency

for subsequent packets.

3.5.4. Frequency Deviation

The peak frequency deviation is configurable from ?.625 to ?20 kHz. The Frequency Deviation (攆) is controlled

by the Frequency Deviation Register (fd), address 71 and 72h, and is independent of the carrier frequency setting.

When enabled, regardless of the setting of the hbsel bit (high band or low band), the resolution of the frequency

deviation will remain in increments of 625 Hz. When using frequency modulation the carrier frequency will deviate

from the nominal center channel carrier frequency by 睌f:

Add R/W Function/Description

POR Def.

79 R/W Frequency Hopping Channel

Select

fhch[7] fhch[6] fhch[5] fhch[4] fhch[3] fhch[2] fhch[1] fhch[0]

00h

7A R/W

Frequency Hopping Step

Size

fhs[7]

fhs[6]

fhs[5]

fhs[4]

fhs[3]

fhs[2]

fhs[1]

fhs[0]

00h

)

]

[

(

]

[

kHz

fhch

fhs

Fnom

rr r

625

]

[

peak deviation

625

]

[

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