ns32491 National Semiconductor Corporation, ns32491 Datasheet - Page 4

• Manufacturer Part Number: ns32491
• Description: Serial Network Interface
• Manufacturer: National Semiconductor Corporation

5 0 Pin Descriptions
Pin No
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Name
COL
RXD
CRS
RXC
SEL
GND
LBK
X1
X2
TXD
TXC
TXE
TX
TX
NC
CAP
VCC
NC
RX
RX
CD
CD
b
a
b
a
b
a
I O
O
O
O
O
O
O
O
O
I
I
I
I
I
I
I
Collision Detect Output A TTL MOS level active high output A 10 MHz
(
output When no signal is present at the collision input COL output will go low
Receive Data Output A TTL MOS level signal This is the NRZ data output
from the digital phase-locked loop This signal should be sampled by the
controller at the rising edge of receive clock
Carrier Sense A TTL MOS level active high signal It is asserted when valid
data from the transceiver is present at the receive input It is de-asserted one
and a half bit times after the last bit at receive input
Receive Clock A TTL MOS level recovered clock When the phase-locked loop
locks to a valid incoming signal a 10 MHz clock signal is activated on this output
This output remains low during idle (5 bit times after activity ceases at receive
input)
Mode Select A TTL level input When high transmit
are at the same voltage in idle state providing a ‘‘zero’’ differential When low
transmit
Negative Supply Pin
Loopback A TTL level active high on this input enables the loopback mode
Crystal or External Frequency Source Input (TTL)
Crystal Feedback Output This output is used in the crystal connection only It
must be left open when driving X1 with an external frequency source
Transmit Data A TTL level input This signal is sampled by the SNI at the rising
edge of transmit clock when transmit enable input is high The SNI combines
transmit data and transmit clock signals into a Manchester encoded bit stream
and sends it differentially to the transceiver
Transmit Clock A TTL MOS level 10 MHz clock signal derived from the 20
MHz oscillator This clock signal is always active
Transmit Enable A TTL level active high data encoder enable input This signal
is also sampled by the SNI at the rising edge of transmit clock
Transmit Output Differential line driver which sends the encoded data to the
transceiver These outputs are source followers and require 270X pulldown
resistors to GND
No Connection
Bypass Capacitor A ceramic capacitor (greater than 0 001 mF) must be
connected from this pin to GND
Positive Supply Pins A 0 1 mF ceramic decoupling capacitor must be
connected across VCC and GND as close to the device as possible
No Connection
Receive Input Differential receive input pair from the transceiver
Collision Input Differential collision input pair from the transceiver
a
25% – 15%) signal at the collision input will produce a logic high at COL
a
is positive with respect to transmit
4
Description
b
in idle state
a
and transmit
b
outputs