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

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Sheet目录49

43页 44页 45页 46页 [47页]

Si4430/31/32-B1

Rev 1.1

6.7. Preamble Length

The preamble detection threshold determines the number of valid preamble bits the radio must receive to qualify a

valid preamble. The preamble threshold should be adjusted depending on the nature of the application. The

required preamble length threshold will depend on when receive mode is entered in relation to the start of the

transmitted packet and the length of the transmit preamble. With a shorter than recommended preamble detection

threshold the probability of false detection is directly related to how long the receiver operates on noise before the

transmit preamble is received. False detection on noise may cause the actual packet to be missed. The preamble

detection threshold is programmed in register 35h. For most applications with a preamble length longer than 32 bits

the default value of 20 is recommended for the preamble detection threshold. A shorter Preamble Detection

Threshold may be chosen if occasional false detections may be tolerated. When antenna diversity is enabled a 20-

bit preamble detection threshold is recommended. When the receiver is synchronously enabled just before the

start of the packet, a shorter preamble detection threshold may be used. Table 14 demonstrates the recommended

preamble detection threshold and preamble length for various modes.

It is possible to use Si4432/31/30 in a raw mode without the requirement for a 010101... preamble. Contact

customer support for further details.

Note: The recommended preamble length and preamble detection threshold listed above are to achieve 0% PER. They may

be shortened when occasional packet errors are tolerable.

6.8. Invalid Preamble Detector

When scanning channels in a frequency hopping system it is desirable to determine if a channel is valid in the

minimum amount of time. The preamble detector can output an invalid preamble detect signal. which can be used

to identify the channel as invalid. After a configurable time set in Register 60h[7:4], an invalid preamble detect

signal is asserted indicating an invalid channel. The period for evaluating the signal for invalid preamble is defined

as (inv_pre_th[3:0] x 4) x Bit Rate Period. The preamble detect and invalid preamble detect signals are available in

"Register 03h. Interrupt/Status 1" and Register 04h. Interrupt/Status 2.

6.9. Synchronization Word Configuration

The synchronization word length for both TX and RX can be configured in Reg 33h, synclen[1:0]. The expected or

transmitted sync word can be configured from 1 to 4 bytes as defined below:

n synclen[1:0] = 00Expected/Transmitted Synchronization Word (sync word) 3.

n synclen[1:0] = 01Expected/Transmitted Synchronization Word 3 first, followed by sync word 2.

n synclen[1:0] = 10Expected/Transmitted Synchronization Word 3 first, followed by sync word 2, followed by

sync word 1.

n synclen[1:0] = 1Send/Expect Synchronization Word 3 first, followed by sync word 2, followed by sync word 1,

followed by sync word 0.

The sync is transmitted or expected in the following sequence: sync 3畇ync 2畇ync 1畇ync 0. The sync word

values can be programmed in Registers 36h39h. After preamble detection, the part will search for sync for a fixed

Table 14. Minimum Receiver Settling Time

Mode

Approximate

Receiver

Settling Time

Recommended Preamble

Length with 8-Bit

Detection Threshold

Recommended Preamble

Length with 20-Bit

Detection Threshold

(G)FSK AFC Disabled

1 byte

20 bits

32 bits

(G)FSK AFC Enabled

2 byte

28 bits

40 bits

(G)FSK AFC Disabled +Antenna

Diversity Enabled

1 byte

64 bits

(G)FSK AFC Enabled +Antenna

Diversity Enabled

2 byte

8 byte

OOK

2 byte

3 byte

4 byte

OOK + Antenna Diversity Enabled

8 byte

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