Cirrus Logic EP93xx - Manual (Page 610)

17-14 DS785UM1
Copyright 2007 Cirrus Logic
IrDA
EP93xx User’s Guide
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17.5.1 Introduction
17.5.1.1 4PPM Modulation
Four position pulse modulation (4PPM) is used for the high-speed transmission rate of
4.0 Mbps. Payload data is divided into data bit pairs (DBPs) for encoding with LSBs
transmitted first. Each DBP is represented by one of four symbols (DDs) comprising a single
125 ms pulse within a 500 ms symbol period. The 125 ms quarters of a symbol are known as
“chips”. The resulting signal waveform for the four data DDs is shown in
Figure 17-2 and
Figure 17-3 and shows modulation of the byte, 10110001b which is constructed using four
DBPs.
Note: 1. Bits within each DBP are not reordered, but the least significant DBP is transmitted first.
Note: 2. A “chip” in the context of the FIR is one time slice in the Position Modulation (PPM)
symbol.
Figure 17-2. 4PPM Modulation Encoding