83C694D Datasheet, PDF (16/33 Pages) SMSC Corporation – Twisted-Pair Interface and Manchester Encoder/Decoder

PIN DESCRIPTION
83C694D
PIN
NUMBER
24
25
26
27
28
29
30
31
MNEMONIC SIGNAL NAME I/O
DESCRIPTION
TPX1+
TPX2+
TX-
TX+
OSR
CAP
MODE1
MODE2
TwPr Transmit
O
TwPr Transmit
O
AUI Transmit
O
VCO Bias Resistor I
PLL Filter Cap
I
Mode Select 1
I
Mode Select 2
I
In 10BaseT operation, data input via TXD is
encoded and then transmitted on TPX pins.
When transmit and receive are idle, Link Test
pulses are periodically transmitted via TPX.
The TPX pins are connected to the twisted-
pair medium via a transformer and filter, and
use 5 external resistors for waveshaping as
shown in Figure 2-6. TPX1+ is the high cur-
rent positive output pin.
TPX2+ is used for 10BaseT only. It is the low
current positive output pin. See TPX1+ for
details.
In AUI mode, TX+ and TX- transmit Manches-
ter encoded data differentially to an external
transceiver. Each output requires an external
pull-up resistor of 150Ω 1% to +5V as shown
in Figure 2-2.
A resistor from OSR to +5V biases the internal
VCO current. Nominal value is 31.6 KΩ 1%.
A capacitor (nominal value .02 µF) from CAP
to ground is used as part of the filter for the
internal phase-locked loop.
With MODE1 low, TP mode is always se-
lected. No Link Test pulses are transmitted or
required on RX+/-. When MODE1 is high, AUI
mode is selected at power on. When MODE1
is connected to RES, 10BaseT mode is se-
lected at power on. After power on, if MODE1
is not low, 10BaseT mode is automatically
selected if LNK goes low (otherwise AUI
mode is selected). The MODE1 pin includes
an internal pull-up resistor, so it can be left
open if not used.
When MODE2 is low, automatic link polarity
correction is disabled (TP mode only). Auto-
polarity correction is enabled when MODE2
is high. The MODE2 pin includes an internal
pull up resistor, so it may be left open if not
used.
TABLE 3-1. PIN DESCRIPTION cont.
13