83C694 Datasheet, PDF (7/33 Pages) List of Unclassifed Manufacturers – TWISTED PAIR INTERFACE AND MACHESTER ENCODER/DECODER

83C694D
ARCHITECTURE
2.0 ARCHITECTURE
The 83C694D can be used as an AUI device or as
a twisted-pair interface device.
When used in combination TPI/AUI applications,
the 83C694D is part of a three-device set that
implements the complete IEEE 802.3-compatible
network node electronics (see Figure 1-1).
The 83C690 Ethernet LAN Controller (ELC) and the
83B692 Ethernet Transceiver (ET) comprise the
other two devices in the set. The 83C690 provides
media access protocol functions and performs buff-
er management tasks, while the 83B692 serves as
a coaxial cable line driver/receiver and collision
detector.
The 83C694D Twisted-Pair Interface provides the
interface between the 83C690 ELC and the 83B692
ET. When transmitting, the device converts non-re-
turn-to-zero (NRZ) data from the controller into
Manchester encoded data, then sends this data to
the transceiver.
When receiving, the device reverses the process
using an analog phase-locked loop that decodes 10
Mbit/sec signals with up to ±20 nsec of jitter.
When the 83C694D is used as a twisted-pair (TP)
interface, its on-chip transmitter and receiver (sepa-
rate from the AUI inputs and outputs) connect to the
network through a transformer and filter. In this
application, the 83C694D is used with the 83C690
providing controller and protocol functions, and the
83B692 is not used.
The 83C694D Twisted-Pair Interface is comprised
of these functional blocks:
• Oscillator
• Manchester Encoder and Differential Driver
• Manchester Decoder
• Collision Translator
• Loopback Capabilities
• TP Differential Driver
• TP Differential Receiver
• Link Test Function
• AUI / TP Autoselect
• Jabber & SQE Test Functions
• Status Indications
The rest of this section describes each of these
circuits in more detail, including suggestions, where
appropriate, for designing external circuits consis-
tent with the 802.3 standard.
2.1 OSCILLATOR
Control is provided either by a 20 MHz, parallel
resonant crystal connected between X1 and X2, or
by an external clock connected at X1. The oscilla-
tor’s 20 MHz output is divided in half to generate
the 10 MHz transmit clock for the Ethernet LAN
controller and to provide the internal clock signals
for the encoding and decoding circuits.
Figure 2-1 provides a diagram of this connection.
X1
20 MHz
X2
CL - CP
CL = Load capacitance specified by crystal manufacturer
CP = Total parasitic capacitance including:
a) 83C694C input capacitance between X1 and X2
(typically 5 pF)
b) PC board traces, plated through holes, socket capacitances
FIGURE 2-1. CRYSTAL CONNECTION
DIAGRAM
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