cs8904 Cirrus Logic, Inc., cs8904 Datasheet - Page 12

• Manufacturer Part Number: cs8904
• Description: Crystal Lan? Quad Ethernet Transceiver
• Manufacturer: Cirrus Logic, Inc.

3.0 THEORY OF OPERATION
3.1 Overview
The CS8904 provides four independent ports for a
multi-port Ethernet system logic device. In terms of
the IEEE 802.3 specification, the CS8904
combines the functions of the Physical Signaling
sublayer (PLS) and the 10BASE-T Medium
Attachment Unit (MAU) for four independent
interface into a single device. Typically, the system
logic device provides multiple Media Access
Control (MAC) interfaces, which connect to the
CS8904. For simplicity, a single port interface of
this system logic device is referred to as a digital
controller throughout this datasheet.
A synchronous bit-serial stream of data is received
and transmitted between the CS8904 and the digital
controller. Digital information that is sent to the
CS8904 from the digital controller is Manchester
encoded and transmitted over the 10BASE-T
wiring system. Data received from the 10BASE-T
wiring system is converted to serial data which is
sent as a bit-serial stream, along with the clock
recovered from the data, to the Ethernet system
logic. Additionally, status and control information
12
System
ASIC
TxENBL
RxDATA
TxDATA
RxCLK
TxCLK
COLL
CIRRUS LOGIC ADVANCED PRODUCT DATABOOK
CD
Figure 4. ENDEC
ENDEC
Decoder
Detector
Encoder
Carrier
& PLL
Clock
is exchanged between the CS8904 and the Ethernet
digital controller. All ports operate independently,
allowing features such as duplex selection, Auto-
Negotiation, and loopback to operate on a per-port
basis.
The CS8904 also incorporates full IEEE-compliant
transmit and receive filtering internally. No
external filters are required and simple isolation
transformers may be used with the 10BASE-T
ports.
3.2 Encoder/Decoder (ENDEC)
The
(ENDEC) circuit is compliant with the relevant
portions of clause 7 of the Ethernet standard
(ISO/IEC 8802-3, 1996). Its primary functions
include performing Manchester encoding of
transmit data, informing the controller when valid
receive data is present (Carrier Detection), and
recovering the clock and NRZ data from incoming
Manchester-encoded data.
Figure 4 provides a block diagram of the ENDEC
and illustrates how it interfaces to the digital
controller and 10BASE-T transceiver.
Crystal LAN™ Quad Ethernet Transceiver
CS8904’s
RX
TX
Transceiver
integrated
10BASE-T
encoder/decoder
DS191PP2
CS8904