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Chapter 3 Hardware
LittleBoard 550 Reference Manual 53
Table 3-21. Ethernet Port 2 Pin/Signal Descriptions (J32)
Pin # Signal Description
1TX+
2TX-
Analog Twisted Pair Ethernet Transmit Differential Pair. These pins transmit the
serial bit stream for transmission on the Unshielded Twisted Pair Cable (UTP).
These signals interface directly with an isolation transformer.
3RX
6RX-
Analog Twisted Pair Ethernet Receive Differential Pair. These pins receive the
serial bit stream from the isolation transformer.
4, 5 Term Termination
7, 8 Term Termination
9 Speed Speed signals (10BaseT or 100BaseT transfer rate) to green LED
10 3.3V +3.3 volts +/- 5%
11 Link Link signals for yellow LED
12 Activity Activity signals for yellow LED
13, 14 Shld Grounded Shield
Note: Termination involves connecting a 75 ohm resistor between the connector and a capacitance
plane created on an inner layer power plane.
Audio Interface (J28)
The audio solution on the LittleBoard 550 is provided by the VT82C686B and the LM4549 audio
CODEC. These two chips use a digital interface to communicate between the two, which is defined by
AC97 and is revision 2.1 compliant. The LittleBoard 550 supports its own audio amplifier (LM4853),
which drives the audio signals into an external audio load. Output signals for the audio interface are
through the 26-pin 2mm connector (J28) to an external board, which has the respective audio
connections on it.
Audio CODEC (LM4549) features
• Analog Mixer Dynamic Range 97dB (typ)
• D/A Dynamic Range 89dB (typ)
• A/D Dynamic Range 90dB (typ)
• AC’97 Rev 2.1 compliant
• 3D Sound circuitry
• High quality Sample Rate Conversion (SRC) from 4kHz to 48kHz
• PC-Beep passthrough to Line Out while reset is held active low
• True Line Level Output with volume control independent of Line Out
Audio Amplifier (LM4853) features
• Dual bridge-connected audio power amplifier
• 2.2W into 4Ω load or 1.1W into 8Ω load.
• Dual Bridge speaker amplifiers
• Stereo headphone amplifier
• External Audio Interface