SI4463 datasheet(32/53 Pages) SILABS

32 / 53 page

Si4463/61/60-C

Rev 1.0

5.3.1.1. EZ Frequency Programming

In applications that utilize multiple frequencies or channels, it may not be desirable to write four API registers each

time a frequency change is required. EZ frequency programming is provided so that only a single register write

(channel number) is required to change frequency. A base frequency is first set by first programming the integer

and fractional components of the synthesizer. This base frequency will correspond to channel 0. Next, a channel

step

size

programmed

into

the

FREQ_CONTROL_CHANNEL_STEP_SIZE_1

and

FREQ_CONTROL_CHANNEL_STEP_SIZE_0 API registers. The resulting frequency will be:

The second argument of the START_RX or START_TX is CHANNEL, which sets the channel number for EZ

frequency programming. For example, if the channel step size is set to 1 MHz, the base frequency is set to

900 MHz with the FREQ_CONTROL_INTE and FREQ_CONTROL_FRAC API properties, and a CHANNEL

number of 5 is programmed during the START_TX command, the resulting frequency will be 905 MHz. If no

CHANNEL argument is written as part of the START_RX/TX command, it will default to the previously-programmed

value. The initial value of CHANNEL is 0; so, if no CHANNEL value is written, it will result in the programmed base

frequency.

5.3.1.2. Automatic RX Hopping and Hop Table

The transceiver supports an automatic RX hopping feature that can be fully configured through the API. This

functionality is useful in applications where it is desired to look for packets but to hop to the next channel if a packet

is not found. The sequence of channel numbers that are visited are specified by entries in a hop table. If this

feature is enabled, the device will automatically start hopping through the channels listed in the hop table as soon

as the chip enters RX mode.

The hop table can hold up to 64 entries and is maintained in firmware inside the RFIC. Each entry is a channel

number, allowing construction of a frequency plan of up to 64 channels. The number of entries in the table is set by

RX HOP TABLE_SIZE API. The specified channels correspond to the EZ frequency programming method for

programming the frequency. The receiver starts at the base channel and hops in sequence from the top of the hop

table to the bottom. The table will wrap around to the base channel once it reaches the end of the table. An entry of

0xFF in the table indicates that the entry should be skipped. The device will hop to the next entry in the table that

contains a non-0xFF value.

There are three conditions that can be used to determine whether to continue hopping or to stay on a particular

channel. These conditions are as follows:



RSSI threshold



Preamble timeout (invalid preamble pattern)



Sync word timeout (invalid or no sync word detected after preamble)

These conditions can be used individually, or they can be enabled all together by configuring the

RX_HOP_CONTROL API. However, the firmware will make a decision on whether or not to hop based on the first

condition that is met.

The RSSI that is monitored is the current RSSI value. This is compared to the threshold value set in the

MODEM_RSSI_THRESH API property, and, if it is above the threshold value, it will stay on the channel. If the

RSSI is below the threshold, it will continue hopping. There is no averaging of RSSI done during the automatic

hopping from channel to channel. Since the preamble timeout and the sync word timeout are features that require

packet handling, the RSSI threshold is the only condition that can be used if the user is in “direct” or “RAW” mode

where packet handling features are not used.

The RSSI threshold value may be converted to an approximate equivalent RF input power level through the

equation shown in "5.2.4. Received Signal Strength Indicator" on page 30. However, performance should be

verified on the bench to optimize the threshold setting for a given application.

The time spent in receive mode will be determined by the configuration of the hop conditions. Manual RX hopping

will have the fastest turn-around time but will require more overhead and management by the host MCU.

RF Frequency

Base Frequency Channel

Stepsi



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