Ampro Corporation Littleboard 550 manual Audio Interface J28

Chapter 3			Hardware
Table 3-21. Ethernet Port 2 Pin/Signal Descriptions (J32)
	Pin #	Signal	Description
	1	TX+	Analog Twisted Pair Ethernet Transmit Differential Pair. These pins transmit the
			serial bit stream for transmission on the Unshielded Twisted Pair Cable (UTP).
	2	TX-
			These signals interface directly with an isolation transformer.
	3	RX	Analog Twisted Pair Ethernet Receive Differential Pair. These pins receive the
			serial bit stream from the isolation transformer.
	6	RX-
	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

LittleBoard 550 Reference Manual 53