82595FX Datasheet, PDF (32/54 Pages) Intel Corporation – ISA BUS HIGH INTEGRATION ETHERNET CONTROLLER

82595FX
9 0 SERIAL INTERFACE
The 82595FX’s serial interface subsystem incorpo-
rates all the active circuitry required to interface the
82595FX to 10BASE-T networks or to the attach-
ment unit (AUI) interface It includes on-chip AUI and
TPE drivers and receivers as well as Manchester
Encoder Decoder and Clock Recovery circuitry The
AUI port can be connected to an Ethernet Trans-
ceiver cable drop to provide a fully compliant IEEE
802 3 AUI interface The AUI port can also be inter-
faced to a transceiver to provide a fully compliant
IEEE 802 3 10BASE2 (Cheapernet) interface The
TPE port provides a fully compliant 10BASE-T inter-
face The 82595FX automatically enables either the
AUI or TPE interface depending on which medium is
active This automatic selection can be overridden
by software configuration The TPE interface also
features a polarity fault detection and correction cir-
cuit which will detect and correct a polarity error on
the twisted pair wire the most common wiring fault
in twisted pair networks
A 20 MHz parallel resonant crystal is used to control
the clock generation oscillator which provides the
basic 20 MHz clock source An internal divide-by-
two counter generates the 10 MHz g0 01% clock
required by the IEEE 802 3 specification
The 82595FX supports 802 3 Half Duplex Ethernet
functionality as did previous versions of the 82595
It also supports a Full Duplex Ethernet mode that
complies with Specifications for Full Duplex Ether-
net Rev 1 0 Sept 9th 1993 from Kalpana when
connected to a Full Duplex hub through the TPE
port Full-duplex provides increased network
throughput (using full duplex network components)
by providing dedicated channels for both Transmit
and Receive data at the same time Full Duplex op-
eration is transparent to existing software drivers
More details on Full Duplex functionality can be
found in the 82595FX User’s Guide
Auto-Negotiation (or N-Way) is a method of maximiz-
ing network operational efficiency Auto-Negotiation
works by interrogating Auto-Negotiation compliant
equipment to determine the highest common mode
of operation shared by all connected devices When
Auto-Negotiation is enabled the 82595FX will nego-
tiate the Highest Common Denominator (HCD)
transmission mode with the hub to which it is at-
tached on a hardware reset If the hub does not
support Auto-Negotiation and Auto-Negotiation is
enabled on the 82595FX the 82595FX will revert to
Half Duplex
The 82595FX is in Auto-Negotiation mode only
when the A-N Enable bit bit 1 in register 13 of bank
2 is set On hardware reset the state of this bit is
copied from the EEPROM A-N Enable bit bit 9 of
Word 0 of the EEPROM
We recommend that a crystal that meets the follow-
ing specifications be used
 Quartz Crystal
 20 00 MHz g0 002% at 25 C
 Accuracy g0 005% over Full Operating Temper-
ature 0 C to ^a70 C
 Parallel resonant with 20 pF Load Fundamental
Mode
Several vendors have such crystals either off-the-
shelf or custom-made Two possible vendors are
1 M-Tron Industries Inc
Yankton SD 57078
Specifications
Part No HC49 with 20 MHz 50 PPM over 0 C to
a_{70 C and 20 pF fundamental load}
2 Crystek Corporation
100 Crystal Drive
Ft Myers FL 33907
Part No 013212
The accuracy of the Crystal Oscillator frequency de-
pends on the PC board characteristics therefore it
is advisable to keep the X1 and X2 traces as short
as possible The optimum value of C1 and C2 should
be determined experimentally under nominal operat-
ing conditions The typical value of C1 and C2 is
between 22 pF and 35 pF
An external 20 MHz MOS-level clock may be applied
to pin X1 if pin X2 is left floating
A summary of the 82595FX’s serial interface sub-
sections functions is shown below
 Manchester Encoder Decoder and Clock
Recovery
 Diagnostic Loopback
 Reset-Low-Power Mode
 Network Status Indicators
 Defeatable Jabber Timer
 User Test Modes
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