Table of Contents
Advertisement
Communication Processor Module
16.9.20.3 HIGH-SPEED IRDA PROTOCOL. The high-speed IrDA protocol is derived from
the preexisting SCCx Transparent protocol standard.
16.9.20.3.1 4PPM Data Encoding. Pulse position modulation (PPM) encoding is achieved
by defining a data symbol duration (Dt) and subsequently subdividing Dt into a set of equal
time slices called "chips". In PPM schemes, each chip position within a data symbol
represents one of the possible bit combinations. Each chip has a duration of Ct given by
Ct = Dt/Base.
In this formula base refers to the number of pulse positions or chips in each data symbol.
The base for high-speed IrDA protocol is defined as four and the resulting modulation
scheme is four-pulse position modulation (4PPM). The data rates of a IrDA PPM system are
defined as 4.0Mb/s.
The resulting values for Ct and Dt are as follows:
• Dt = 500 ns
• Ct = 125 ns
The figure below illustrates a data symbol field and its enclosed chip durations for a 4PPM
scheme.
Because there are four unique chip positions within each symbol in 4PPM, four independent
symbols exist in which only one chip is logically a "one" while other chips are logically a
"zero". These four unique symbols are the only legal data symbols (DD) allowed in 4PPM.
Each data symbol represents two bits of payload data, or a single data bit pair (DBP), so that
a byte of payload data can be represented by four data symbols in sequence. The following
table defines the chip pattern representation of the four unique data symbols defined for
4PPM.
16-290
CHIP1
CHIP2
CHIP3
Figure 16-97. One Complete Symbol
DATA BIT PAIR
4PPM DATA SYMBOL
00
01
10
11
MPC823e REFERENCE MANUAL
CHIP4
1000
0100
0010
0001
MOTOROLA
Advertisement
Table of Contents
