mpc823rg Freescale Semiconductor, Inc, mpc823rg Datasheet - Page 739

• Manufacturer Part Number: mpc823rg
• Description: Mpc823 Powerquicc Integrated Communications Processor For Portable Systems
• Manufacturer: Freescale Semiconductor, Inc

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:
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.
• Dt = 500 ns
• Ct = 125 ns
Freescale Semiconductor, Inc.
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Figure 16-95. One Complete Symbol
CHIP1
DATA BIT PAIR
MPC823 REFERENCE MANUAL
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00
01
10
11
CHIP2
4PPM DATA SYMBOL
CHIP3
1000
0100
0010
0001
CHIP4
Communication Processor Module
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