11-2
Intel® PXA255 Processor
Developer’s Manual
Fast Infrared Communication Port
11.2.1
4PPM Modulation
Four-position pulse modulation (4PPM) is used to transmit data at the high-speed rate, 4.0 Mbps.
Data bits are encoded two at a time by placing a single 125 ns light pulse in one of four timeslots.
The four timeslots are collectively termed a chip. Bytes are encoded one at a time. They are divided
into four individual 2-bit pairings called nibbles. The least significant nibble is transmitted first.
Figure 11-1
shows the 4PPM encoding for the possible 2-bit combinations and
Figure 11-2
shows
an example of 4PPM modulation for the byte 0b10110001, which is constructed with four chips.
Bits within each nibble are not reordered, but nibble 0 (least significant) is transmitted first and
nibble 3 (most significant) is transmitted last.
Figure 11-1. 4PPM Modulation Encodings
Chip
Timeslots
1
2
3
4
Data = 0b00
Data = 0b01
Data = 0b10
Data = 0b11
Figure 11-2. 4PPM Modulation Example
4PPM
Data
Reordered
Nibbles
0
1
0
0
1
1
1
0
125 ns
Timeslots
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
Chips
1
2
3
4
Receive data sample counter frequency = 6/pulse width. Each timeslot is sampled on the third clock.
Original
Byte Order
1
0
1
1
0
0
0
1
Nibble 3
Nibble 2
Nibble 1
Nibble 0
Nibble 0
Nibble 1
Nibble 2
Nibble 3
48 MHz
Summary of Contents for PXA255
Page 1: ...Intel PXA255 Processor Developer s Manual January 2004 Order Number 278693 002 ...
Page 24: ...xxiv Intel PXA255 Processor Developer s Manual Contents ...
Page 30: ...1 6 Intel PXA255 Processor Developer s Manual Introduction ...
Page 310: ...7 46 Intel PXA255 Processor Developer s Manual LCD Controller ...
Page 330: ...8 20 Intel PXA255 Processor Developer s Manual Synchronous Serial Port Controller ...
Page 358: ...9 28 Intel PXA255 Processor Developer s Manual I2 C Bus Interface Unit ...
Page 488: ...13 36 Intel PXA255 Processor Developer s Manual AC 97 Controller Unit ...
Page 572: ...16 30 Intel PXA255 Processor Developer s Manual Network SSP Serial Port ...
Page 599: ...Intel PXA255 Processor Developer s Manual 17 27 Hardware UART ...
Page 600: ......