SI4464 datasheet(33/56 Pages) SILABS

33 / 56 page

Si4464/63/61/60

Rev 1.2

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 INTE and FRAC API registers, 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 previous 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 hopping feature that can be fully configured through the API. This is

intended for RX hopping where the device has to hop from channel to channel and look for packets. Once the

device is put into the RX state, it automatically starts hopping through the hop table if the feature is enabled.

The hop table can hold up to 64 entries and is maintained in firmware. Each entry is a channel number; so, the hop

table can hold 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 non 0xFF entry.

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

channel. These conditions are:



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, 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.

Note that the RSSI threshold is not an absolute RSSI value; instead, it is a relative value and should be verified on

the bench to find an optimal threshold for the application.

The turnaround time from RX to RX on a different channel using this method is 115 µs. 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.

The following are example steps for using Auto Hop:

1. Set the base frequency (inte + frac) and channel step size.

2. Define the number of entries in the hop table (RX_HOP_TABLE_SIZE).

3. Write the channels to the hop table (RX_HOP_TABLE_ENTRY_n)

4. Configure the hop condition and enable auto hopping- RSSI, preamble, or sync (RX_HOP_CONTROL).

5. Set preamble and sync parameters if enabled.

RF Frequency

Base Frequency Channel

Stepsi



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