CS8904
Crystal LAN™ Quad Ethernet Transceiver
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.
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.
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 CS8904’s integrated encoder/decoder
(ENDEC) circuit is compliant with the relevant
portions of clause 7 of the Ethernet standard
(ISO/IEC 8802-3, 1996). Its primary functions
A synchronous bit-serial stream of data is received
and transmitted between the CS8904 and the digital include performing Manchester encoding of
controller. Digital information that is sent to the transmit data, informing the controller when valid
CS8904 from the digital controller is Manchester
encoded and transmitted over the 10BASE-T
receive data is present (Carrier Detection), and
recovering the clock and NRZ data from incoming
wiring system. Data received from the 10BASE-T Manchester-encoded data.
wiring system is converted to serial data which is
Figure 4 provides a block diagram of the ENDEC
and illustrates how it interfaces to the digital
controller and 10BASE-T transceiver.
sent as a bit-serial stream, along with the clock
recovered from the data, to the Ethernet system
logic. Additionally, status and control information
ENDEC
Carrier
Detector
CD
10BASE-T
Transceiver
RX
TX
RxCLK
Decoder
& PLL
RxDATA
System
ASIC
TxCLK
TxDATA
TxENBL
Encoder
COLL
Clock
Figure 4. ENDEC
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