DP8391 NS32491 Serial Network Interface
July 1986
DP8391 NS32491 Serial Network Interface
General Description
The DP8391 Serial Network Interface (SNI) provides the
Manchester data encoding and decoding functions for
IEEE 802 3 Ethernet Cheapernet type local area networks
The SNI interfaces the DP8390 Network Interface Controller
(NIC) to the Ethernet transceiver cable When transmitting
the SNI converts non-return-to-zero (NRZ) data from the
controller and clock pulses into Manchester encoding and
sends the converted data differentially to the transceiver
The opposite process occurs on the receive path where a
digital phase-locked loop decodes 10 Mbit s signals with as
much as
g
20 ns of jitter
The DP8391 SNI is a functionally complete Manchester en-
coder decoder including ECL like balanced driver and re-
ceivers on board crystal oscillator collision signal transla-
tor and a diagnostic loopback circuit
The SNI is part of a three chip set that implements the com-
plete IEEE compatible network node electronics as shown
below The other two chips are the DP8392 Coax Transceiv-
er Interface (CTI) and the DP8390 Network Interface Con-
troller (NIC)
Incorporated into the CTI are the transceiver collision and
jabber functions The Media Access Protocol and the buffer
management tasks are performed by the NIC There is an
isolation requirement on signal and power lines between the
CTI and the SNI This is usually accomplished by using a set
of miniature pulse transformers that come in a 16-pin plastic
DIP for signal lines Power isolation however is done by
using a DC to DC converter
Features
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Compatible with Ethernet II IEEE 802 3 10base5 and
10base2 (Cheapernet)
10 Mb s Manchester encoding decoding with receive
clock recovery
Patented digital phase locked loop (DPLL) decoder re-
quires no precision external components
Decodes Manchester data with up to
g
20 ns of jitter
Loopback capability for diagnostics
Externally selectable half or full step modes of opera-
tion at transmit output
Squelch circuits at the receive and collision inputs re-
ject noise
High voltage protection at transceiver interface (16V)
TTL MOS compatible controller interface
Connects directly to the transceiver (AUI) cable
Table of Contents
1 0 System Diagram
2 0 Block Diagram
3 0 Functional Description
31
Oscillator
32
Encoder
33
Decoder
34
Collision Translator
35
Loopback
4 0 Connection Digram
5 0 Pin Description
6 0 Absolute Maximum Ratings
7 0 Electrical Characteristics
8 0 Switching Characteristics
9 0 Timing and Load Diagrams
10 0 Physical Dimensions
1 0 System Diagram
IEEE 802 3 Compatible Ethernet Cheapernet Local Area Network Chip Set
TL F 6758 鈥?1
C
1995 National Semiconductor Corporation
TL F 6758
RRD-B30M115 Printed in U S A
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