AN626

PACKET HANDLER OPERATION FOR Si446X RFICS

1. Introduction

This application note discusses the operation of the Packet Handler (PH) on the Si446x family of RFICs. Details of

operation in both TX mode and RX mode are provided. The purpose of this application note is to expand upon the

information available in the data sheets for Si446x devices. This application note does not discuss direct mode or

raw data mode (as may be required by legacy systems with non-standard packet structures). A thorough

understanding of the topics discussed within this application note will be helpful in construction of a typical packet

structure such as that shown in Figure 1.

Figure 1. General Packet Structure

In order to completely specify the structure of the packet, it is necessary to configure the Preamble, Sync Word,

and Data fields. Configuration of these fields is provided by four groups of properties accessible through the API:

Property Group 0x10xx=Preamble Configuration

Property Group 0x11xx=Sync Word Configuration

Property Group 0x12xx=Packet Field Configuration

Property Group 0x30xx=Ma tch (Header Check) Configuration

Although the PH itself is concerned only with configuration of the Packet Fields (property group 0x12xx), all four

property groups are discussed within this document; a thorough understanding of configuration of these groups is

required to construct a desired packet structure.

It is assumed that the user has a basic familiarity with the API for the Si446x family of RFICs. All configurations of

the PH discussed within this application note are a cco m plish e d thro ug h th e us e of pu blishe d API calls.

1-255 Bytes 1-4 Bytes

0, 2, or 4

Bytes

Sync Word

Preamble

CRC Field 1 (opt)

Field 1

Header or Da ta

Fi el d 2 (opt)

Pkt Length or Data

CRC Field 2 (opt)

Field 3 ( opt )

Data

CRC Field 3 (opt)

Field 4 ( opt )

Data

CRC Field 4 (opt)

Field 5 ( opt )

Data

CRC Field 5 (opt)

Config Config

0, 2, or 4

Bytes

Config

0, 2, or 4

Bytes

0, 2, or 4

Bytes

0, 2, or 4

Bytes

Config Config

AN626

2 Rev. 0.2

2. Packet Handler Overview

The Si446x family of chips contains circuit functionality known as the automatic Packet Handler (PH). The purpose

of the PH is to automatically perform basic packet structure construction (in TX mode) or deconstruction (in RX

mode), without the need for MCU control or intervention. The usual fields needed for packet generation (such as

Preamble and Sync Word) normally change infrequently and can therefore be stored in registers. Automatically

adding these fields to the Pa yload data g reatly re duces the required computational power of the MCU, allowing use

of a less-complex (i.e., cheaper) MCU.

The PH has little benefit unless the chip is also operated in FIFO mode (as opposed to Direct mode where the bits

of the transmit or receive data stream are processed in real-time on a physical input or output pin). Therefore,

operation of the chip in FIFO mode is assumed throughout this document, unless noted otherwise.

The functionality of the PH may be enabled or disabled in RX mode. Enabling/disabling of the PH functionality is

provided in Property 0x1206 PKT_CONFIG1 by the PH_RX_DISABLE bit D6. However, if the PH is disabled the

receiver may only be oper ated in Direc t mode; o peration in FIFO mo de is n ot p ossible. T he PH remain s en abled at

all times in TX mode.

Figure 2. Property 0x1206 PKT_CONFIG1, General Packet Configuration Bits

The functionality of the PH includes the following:

Detection/validation of Preamble quality in RX mode (PREAMBLE_VALID signal)

Detection of Sync word in RX mode (SYNC_OK signal)

Detection of valid packets in RX mode (PKT_VALID signal)

Detection of CRC errors in RX mode (CRC_ERR signal)

Data de-whitening and/or Manchester decoding (if enabled) in RX mode

Match/Header checking in RX mode

Storage of Data Field bytes into FIFO memory in RX mode

Construction of Preamble field in TX mode

Construction of Sync field in TX mode

Construction of Data Field from FIFO memory in TX mode

Construction of CRC field (if enabled) in TX mode

Data whitening and/or Manchester encoding (if enabled) in TX mode