DP83932C-20 Datasheet, PDF (3/98 Pages) National Semiconductor (TI) – MHz SONICTM Systems-Oriented Network Interface Controller

1 0 Functional Description
The SONIC (Figure 1-1 ) consists of an encoder decoder
(ENDEC) unit media access control (MAC) unit separate
receive and transmit FIFOs a system buffer management
engine and a user programmable system bus interface unit
on a single chip SONIC is highly pipelined providing maxi-
mum system level performance This section provides a
functional overview of SONIC
1 1 IEEE 802 3 ENDEC UNIT
The ENDEC (Encoder Decoder) unit is the interface be-
tween the Ethernet transceiver and the MAC unit It pro-
vides the Manchester data encoding and decoding func-
tions for IEEE 802 3 Ethernet Thin-Ethernet type local area
networks The ENDEC operations of SONIC are identical to
the DP83910A CMOS Serial Network Interface device Dur-
ing transmission the ENDEC unit combines non-return-zero
(NRZ) data from the MAC section and clock pulses into
Manchester data and sends the converted data differentially
to the transceiver Conversely during reception an analog
PLL decodes the Manchester data to NRZ format and re-
ceive clock The ENDEC unit is a functionally complete
Manchester encoder decoder incorporating a balanced
driver and receiver on-board crystal oscillator collision sig-
nal translator and a diagnostic loopback The features in-
clude
 Compatible with Ethernet I and II IEEE 802 3 10base5
and 10base2
 10Mb s Manchester encoding decoding with receive
clock recovery
 Requires no precision components
 Loopback capability for diagnostics
 Externally selectable half or full step modes of operation
at transmit output
 Squelch circuitry at the receive and collision inputs reject
noise
 Connects to the transceiver (AUI) cable via external
pulse transformer
1 1 1 ENDEC Operation
The primary function of the ENDEC unit (Figure 1-2 ) is to
perform the encoding and decoding necessary for compati-
bility between the differential pair Manchester encoded data
of the transceiver and the Non-Return-to-Zero (NRZ) serial
data of the MAC unit data line In addition to encoding and
decoding the data stream the ENDEC also supplies all the
necessary special signals (e g collision detect carrier
sense and clocks) to the MAC unit The signals provided to
the MAC unit from the on-chip ENDEC are also provided as
outputs to the user
Manchester Encoder and Differential Output Driver
During transmission to the network the ENDEC unit trans-
lates the NRZ serial data from the MAC unit into differential
pair Manchester encoded data on the Coaxial Transceiver
Interface (e g National’s DP8392) transmit pair To perform
this operation the NRZ bit stream from the MAC unit is
passed through the Manchester encoder block of the
ENDEC unit Once the bit stream is encoded it is transmit-
ted out differentially to the transmit differential pair through
the transmit driver
Manchester Decoder During reception from the network
the differential receive data from the transceiver (e g the
DP8392) is converted from Manchester encoded data into
NRZ serial data and a receive clock which are sent to the
receive data and clock inputs of the MAC unit To perform
this operation the signal once received by the differential
receiver is passed to the phase locked loop (PLL) decoder
block The PLL decodes the data and generates a data re-
ceive clock and a NRZ serial data stream to the MAC unit
Special Signals In addition to performing the Manchester
encoding and decoding function the ENDEC unit provides
control and clocking signals to the MAC unit The ENDEC
sends a carrier sense (CRS) signal that indicates to the
MAC unit that data is present from the network on the
ENDEC’s receive differential pair The MAC unit is also pro-
vided with a collision detection signal (COL) that informs the
MAC unit that a collision is taking place somewhere on
FIGURE 1-1 SONIC Block Diagram
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