AMD Advanced Micro Devices AM7992BPC, AM7992BJCTR, AM7992BJC, AM7992BDCB, AM7992BDC Datasheet

FINAL

Publication# 03378 Rev: I Amendment/0
Issue Date: May 1993

1

Am7992B

Serial Interface Adapter (SIA)

DISTINCTIVE CHARACTERISTICS

■

Compatible with lEEE 802.3/Ethernet/Cheapernet
specifications

■

Crystal/TTL oscillator-controlled Manchester
encoder

■

Manchester decoder acquires clock and data
within four bit times with an accuracy of ± 3 ns

■

Guaranteed carrier and collision detection
squelch threshold limits

—Carrier/collision detected for inputs greater than

–275 mV

—No carrier/collision for inputs less than –175 mV

■

Input signal conditioning rejects transient noise

—Transients <10 ns for collision detector inputs
—Transients <20 ns for carrier detector inputs

■

Receiver decodes Manchester data with worst
case ± 19 ns of clock jitter (at 10 MHz)

■

TTL-compatible host interface

■

Transmit accuracy +0.01% (without adjustments)

GENERAL DESCRIPTION

The Am7992B Serial Interface Adapter (SIA) is a
Manchester encoder/decoder compatible with IEEE

802.3, Cheapernet, and Ethernet specifications. In an
IEEE 802.3/Ethernet application, the Am7992B inter­faces the Am7990 Local Area Network Controller for
Ethernet (LANCE) to the Ethernet transceiver device,

acquires clock and data within four bit times, and de­codes Manchester data with worst case ± 19 ns phase
jitter at 10 MHz. SIA provides both guaranteed signal
threshold limits and transient noise suppression cir­cuitry in both data and collision paths to minimize false
start conditions.

BLOCK DIAGRAM

03378I-1

Manchester

Decoder

Data

Receiver

Noise

Reject

Filter

Carrier

Detect

Noise

Reject

Filter

Collision

Detect

Manchester

Encoder

Crystal

OSC

Receive Data (RX)

Receive Clock (RCLK)

Carrier Present (RENA)

Collision (CLSN)

Transmit Data (TX)

Transmit Enable (TENA)

Transmit Clock (TCLK)

20 MHz

XTAL

1

XTAL

2

Receive+

Receive–

Collision+

Transmit+
Transmit–

Collision–

Controller Interface

Transceiver Interface

AMD

2 Am7992B

RELATED PRODUCTS

Part No. Description

Am7990 Local Area Network Controller for Ethernet (LANCE)
Am7996 IEEE 802.3/Ethernet/Cheapernet/Transceiver
Am79C900 Integrated Local Area Communications Controller

TM

(ILACCTM)

CONNECTION DIAGRAMS

Receive+

Collision–

DIP

CLSN

TCLK

Collision+

TEST

Transmit+

TX

GND1

RCLK

RX

Receive–

V

CC1

PF

TENA

1

3

5

7

9

11
12

10

2

4

8

6

24

22

20

18

16

14
13

15

23

21

17

19

RENA

TSEL

X1

GND2

RF
GND3

Transmit–

X2

V

CC2

Note:

Pin 1 is marked for orientation.

PLCC

03378I-2 03378I-3

1

234

2827

26

255
24
23
22

21
20
19

1817

1615

6
7
8

9
10
11

121314

RCLK

NC

TSEL

GND1

GND2

X1
X2

Receive-

TEST

V

CC1

NC
V

CC2

PF
RF

GND3

Transmit+

Transmit-

NC

TX

TCLK

TENA

NC

CLSN

RX

RENA

Colision+

Colision-

Receive+

Am7992B 3

ORDERING INFORMATION
Standard Products

AMD standard products are available in several packages and operating ranges. The order number (valid combination) is formed
by a combination of the elements below.

Valid Combinations

Valid combinations list configurations planned to be sup­ported in volume for this device. Consult the local AMD sales
office to confirm availability of specific valid combinations and
to check on newly released combinations.

AM7992B D C

DEVICE NUMBER/DESCRIPTION

Am7992B
Serial Interface Adapter

OPTIONAL PROCESSING

Blank=Standard Processing
B=Burn-In

OPERATING CONDITIONS

C = Commercial (0°C to +70°C)

PACKAGE TYPE

D=24-Pin (Slim) Ceramic DIP (CD3024)
J=28-Pin PLCC (PL 028)
P=24-Pin (Slim) Plastic DIP (PD3024)

SPEED

Not Applicable

B

Valid Combinations

AM7992B

DC, DCB, JC,

JCTR, PC

4 Am7992B

PIN DESCRIPTION
CLSN

Collision (Output, TTL Active HIGH)

Signals at the Collision ±

terminals meeting threshold
and pulse-width requirements will produce a logic
HIGH at CLSN output. When no signal is present at
Collision ± , CLSN output will be LOW.

RX

Receive Data (Output)

A MOS/TTL output, recovered data. When there is no
signal at Receive ± and TEST

is HIGH, RX is HIGH. RX
is actuated with RCLK and remains active until RENA
is deasserted at the end of the message. During recep­tion, RX is synchronous with RCLK and changes after
the rising edge of RCLK. When TEST

is LOW, RX is

enabled.

RENA

Receive Enable (Output, TTL Active HIGH)

When there is no signal at Receive+, RENA is LOW.
Signals meeting threshold and pulse-width “on” re­quirements will produce a logic HIGH at RENA. When
RENA is HIGH, Receive+ signals meeting threshold
and pulse-width “off” requirements will produce a LOW
at RENA.

RCLK

Receive Clock (Output)

A MOS/TTL output, recovered clock. When there is no
signal at Receive ± and TEST

is HIGH, RCLK is LOW.
RCLK is activated 1/4 bit time after the second negative
Manchester preamble clock transition at Receive ± and
remains active until after an end of message. When
TEST is LOW, RCLK is enabled and meets minimum
pulse-width specifications.

TX

Transmit (Input)

TTL-compatible input. When TENA is HIGH, signals at
TX meeting setup and hold time to TCLK will be
encoded as normal Manchester at Transmit+ and
Transmit–.

■

TX HIGH: Transmit+ is negative with respect to
Transmit– for first half of data bit cell.

■

TX LOW: Transmit+ is positive with respect to
Transmit– for first half of data bit cell.

TENA

Transmit Enable (Input)

TTL-compatible input. Active HIGH data encoder
enable. Signals meeting setup and hold time to TCLK
will allow encoding of Manchester data from TX to
Transmit+ and Transmit–.

TCLK

Transmit Clock (Output)

MOS/TTL output. TCLK provides symmetrical HIGH
and LOW clock signals at data rate for reference timing
of data to be encoded. It also provides clock signals for
the controller chip (Am7990—LANCE) and an internal
timing reference for receive path voltage-controlled
oscillators.

Transmit+, Transmit–

Transmit (Outputs)

A differential line output. This line pair is intended to op­erate into terminated transmission lines. For signals
meeting setup and hold time to TCLK at TENA and TX,
Manchester clock and data are outputted at Transmit+/
Transmit–. When operating into a 78 Ω terminated
transmission line, signaling meets the required output
levels and skew for both Ethernet and IEEE 802.3 drop
cables.

Receive+, Receive–

Receiver (Inputs)

A differential input. A pair of internally biased line re­ceivers consisting of a carrier detect receiver with offset
threshold and noise filtering to detect the line activity,
and a data recovery receiver with no offset for
Manchester data decoding.

Collision+, Collision–

Collision (Inputs)

A differential input. An internally biased line receiver
input with offset threshold and noise filtering. Signals at
Collision ± have no effect on data-path functions.

TSEL

Transmit Mode Select (Output, Open Collector;
Input, Sense Amplifier)

■

TSEL LOW: Idle transmit state Transmit+ is positive
with respect to Transmit–.

■

TSEL HIGH: Idle transmit state Transmit+ and
Transmit– are equal, providing “zero” differential to
operate transformer-coupled loads.

When connected with an RC network, TSEL is held
LOW during transmission. At the end of transmission
the open collector output is disabled, allowing TSEL to
rise and provide a smooth transmission from logic
HIGH to “zero” differential idle. Delay and output return
to zero are externally controlled by the RC network at
TSEL and Transmit ± load inductance.

Am7992B 5

X

1

, X

2

Biased Crystal Oscillator (Input)

X

1

is the input and X

2

is the bypass port. When con­nected for crystal operation, the system clock that ap­pears at TCLK is half the frequency of the crystal
oscillator. X

1

may be driven from an external source of

two times the data rate.

RF

Frequency Setting Voltage-Controlled Oscillator
(V

CO

) Loop Filter (Output)

This loop filter output is a reference voltage for the re­ceive path phase detector. It also is a reference for tim­ing noise immunity circuits in the collision and receive
enable path. Nominal reference V

CO

gain is 1.25 TCLK

frequency MHz/V.

PF

Receive Path V

CO

Phase-Locked Loop Filter (Input)

This loop filter input is the control for receive path loop
damping. Frequency of the receive V

CO

is internally lim-

ited to transmit frequency ± 12%. Nominal receive V

CO

gain is 0.25 reference V

CO

gain MHz/V.

TEST

Test Control (Input)

A static input that is connected to V

CC

for Am7992B/
Am7990 operation and to ground for testing of
Receive ± path threshold and RCLK output HIGH
parameters. When TEST

is grounded, RX is enabled
and RCLK is enabled except during clock acquisition,
when RCLK is HIGH.

GND1

High Current Ground

GND2

Logic Ground

GND3

Voltage-Controlled Oscillator Ground

V

CC1

High Current and Logic Supply

V

CC2

Voltage-Controlled Oscillator Supply

6 Am7992B

FUNCTIONAL DESCRIPTION

The Am7992B serial interface adapter (SIA) has three
basic functions. It is a Manchester encoder/line driver
in the transmit path, a Manchester decoder with noise
filtering and quick lock-on characteristics in the receive
path, and a signal detector/converter (10 MHz differen­tial to TTL) in the collision path. In addition, the SIA pro­vides the interface between the TTL logic environment
of the Local Area Network Controller for Ethernet
(LANCE) and the differential signaling environment in
the transceiver cable.

Transmit Path

The transmit section encodes separate clock and NRZ
data input signals meeting the setup and hold time to
TCLK at TENA and TX into a standard Manchester II
serial bit stream. The transmit outputs (Transmit+/
Transmit–) are designed to operate into terminated
transmission lines. When operating into a 78 Ω termi­nated transmission line, signaling meets the required
output levels and skew for IEEE 802.3/Ethernet/
Cheapernet.

Transmitter Timing and Operation

A 20 MHz fundamental mode crystal oscillator provides
the basic timing reference in the SIA. It is divided by two
to create the Transmit Clock reference (TCLK). Both
20 MHz and 10 MHz clocks are fed into the Manchester
Encoder to generate the transitions in the encoded
data stream. The 10 MHz clock, TCLK, is used by the
SIA to internally synchronize Transmit (TX) data and
Transmit Enable (TENA). TCLK is also used as a stable
bit rate clock by the receive section of the SIA and by
other devices in the system (the Am7990 LANCE uses
TCLK to drive its internal state machine). The oscillator
may use an external 0.005% crystal or an external
TTL-level input as a reference, which will achieve a
transmit accuracy of 0.01% (no external adjustments
are required).

Transmission is enabled when TENA is activated. As
long as TENA remains HIGH, signals at TX will be en­coded as Manchester and will appear at Transmit+ and
Transmit–. When TENA goes LOW, the differential
transmit outputs go to one of two idle states determined
by the circuit configuration of TSEL:

TSEL HIGH: The idle state of Transmit ± yields “zero”

differential to operate transformer-coupled loads (see
Figure 2, Transmitter Timing—End of Transmission
waveform diagram and Typical Performance Curve
diagram).

TSEL LOW: In this idle state, Transmit+ is positive to

Transmit– (logical HIGH) (see figures and diagrams as
referenced above).

The End of Transmission—Return to Zero is deter­mined by the external RX network at TSEL and by the
load at Transmit ± .

Manchester

Encoder

OSC

DO±

TX

TENA

TCLK

I

03378I-4

Figure 1. Transmit Section

VCC

680 pF

3K

C1

R2

20 pF

510

R1

C2

TSEL
PIN 5

A. TSEL LOW B. TSEL HIGH

TSEL
PIN 5

03378I-5 03378I-6

Figure 2. Transmit Mode Select (TSEL) Connection

Am7992B 7

Figure 3. TTL Clock Driver Circuit for X

1

SIA Oscillator

Specification for External Crystal

When using a crystal to drive the Am7992B oscillator,
the following crystal specification should be used to en­sure a transmit accuracy of 0.01%:

Some crystal manufacturers have generated crystals
to this specification. One such manufacturer is Reeves­Hoffman. Their ordering part number for this crystal is
RH#04-20423-312. Another manufacturer is Epson—
Part #MA 506-200M-50 pF, which is a surface­mounted crystal.

Specification for External TTL Level

When driving the oscillator from an external clock
source, X

2

must be left floating (unconnected). An

external clock having the following characteristics
must be used to ensure less than +0.5 ns jitter at
Transmit+ (see the X

1

Driven from External Source
waveform diagram and the TTL Clock Driver Circuit
for X1, Figure 3):

■Clock Frequency: 20 MHz ±0.01%

■Rise/Fall Time (tR/tF): <4 ns, monotonic

■X1 HIGH/LOW Time (t

HlGH/tLOW

): > 20 ns

■X1 Falling Edge-to-Falling Edge Jitter: < ±0.2 ns at

1.5 V input

Receiver Path

The principle functions of the receiver are to signal the
LANCE that there is information on the receive pair and
to separate the incoming Manchester-encoded data
stream into clock and NRZ data.

The receiver section (see Figures 4 and 5) consists of
two parallel paths. The receive data path is a zero
threshold, wide bandwidth line receiver. The carrier
path is an offset threshold bandpass-detecting line re­ceiver. Both receivers share common bias networks to
allow operation over an input common mode range of
0 V to 5.5V.

Limit

UnitMin Nominal Max

Resonant Frequency
Error with C

L

= 50 pF

–50 0 +50 PPM

Change in Resonant
Frequency Temperature
with C

L

= 50 pF

–40 +40 PPM

Parallel Resonant
Frequency with
C

L

= 50 pF

20 MHz

Motional Crystal
Capacitance, C

1

0.022 pF

X

1

ALS Driver or

Equivalent

03378I-7

Manchester

Decoder

Data

Receiver

Noise

Reject

Filter

Carrier
Detect

RX

RCLK

RENA

DI±

03378I-8

Figure 4. Receiver

8 Am7992B

Input Signal Conditioning

The Carrier Receiver detects the presence of an in­coming data packet by discerning and rejecting noise
from expected Manchester data. It also controls the
stop and start of the phase-locked loop during clock ac­quisition. In the Am7992B, clock acquisition requires a
valid Manchester bit pattern of 1010 to lock on the in­coming message (see Receive Timing—Start of Re­ception Clock Acquisition waveform diagram).

Transient noise pulses less than 20 ns wide are re­jected by the Carrier Receiver as noise and DC inputs
more positive than –175 mV are also suppressed. Car­rier is detected for input signal wider than 45 ns with
amplitude more negative than –275 mV. When input
amplitude and pulse-width conditions are met at
Receive±, RENA is asserted and a clock acquisition
cycle is initiated.

Clock Acquisition

When there is no activity at Receive± (receiver is idle),
the receive oscillator is phase locked to TCLK. The first
negative clock transition (first valid Manchester “0”)
after RENA is asserted interrupts the receive oscillator
and presets the INTRCLK (internal clock) to the HIGH
state. The oscillator is then restarted at the second
Manchester “0” (bit time 4) and is phase locked to it. As
a result, the SIA acquires the clock from the incoming
Manchester bit stream in four bit times with a “1010”
Manchester bit pattern. The 10 MHz INTRCLK and
INTPLLCLK are derived from the internal oscillator,
which runs at four times the data rate (40.0 MHz). The
three clocks generated internally are utilized in the fol­lowing manner:

■INTRCLK: After clock acquisition, INTRCLK
strobes the incoming data at 1/4 bit time. Receive
data path sets the input to the data decode register
(Figure 5).

■INTPLLCLK: At clock acquisition, INTPLLCLK is
phase locked to the incoming Manchester clock
transition at bit cell center (BCC). The transition at

BCC is compared to INTPLLCLK and phase correc­tion is applied to maintain INTRCLK at 1/4 bit time
in the Manchester cell.

■INTCARR: From start to end of a message,
INTCARR is active and establishes RENA turn-off
synchronously with RCLK rising edge. Internal car­rier goes active when there is a negative transition
that is more negative than –275 mV and has a pulse
width greater or equal to 45 ns. Internal carrier goes
inactive typically 155 ns after the last positive tran­sition at Receive±.

When TEST is strapped LOW, RCLK and RX are en­abled 1/4 bit time after clock acquisition in bit cell 5. RX
is at HIGH state when the receiver is idle and TEST is
strapped HIGH (no RLCK). RX, however, is undefined
when clock is acquired and may remain HIGH or
change to LOW state whenever RCLK is enabled. At
the 1/4 bit time of clock transition in bit cell 5, RCLK
makes its first external transition. It also strobes the in­coming fifth bit Manchester “1.” RX may make a transi­tion after the RCLK rising edge in bit cell 5, but its state
is still undefined. The Manchester “1” at bit 5 is clocked
to RX output at 1/4 bit time in bit cell 6.

PLL Tracking

After clock acquisition, the INTPLLCLK is compared to
the incoming transitions at BCC and the resulting
phase error is applied to a correction circuit. This circuit
ensures that INTPLLCLK remains locked on the re­ceived signal. Individual bit cell phase corrections of
the VCO are limited to 10% of the phase difference be­tween BCC and INTPLLCLK. Hence, input data jitter is
reduced in RCLK by 10 to 1.

Carrier Tracking and End of Message

The carrier receiver monitors Receive± input after
RENA is asserted for an end of message. INTCARR
deasserts typically 155 ns to 165 ns after the incoming
message transitions positive. This initiates the end of
reception cycle. INTCARR is strobed at 3/4 bit time by
the falling edge of INTRCLK. The time delay from the

03378I-9

Figure 5. Receiver Section Detail

RX

RCLK

RENA

Q D

Clock

Gating

DIV

40.0 MHz
V

CO

Phase

Detector

Noise

Reject

Filter

+

–

+

Carrier

REC

Data
REC

Am7992B 9

last rising edge of the message to INTCARR deassert
allows the last bit to be strobed by RCLK and trans­ferred by the LANCE without an extra bit at the end of
the message. When RENA deasserts (see Receive
Timing—End of Reception waveform diagrams), a
RENA hold-off timer inhibits RENA assertion for at
least 120 ns.

Data Decoding

The data receiver is a comparator with clocked output
to minimize noise sensitivity to the Receive± inputs.
Input error (VIRD) is less than ±35 mV to minimize sen­sitivity to input rise and fall time. RCLK strobes the data
receiver output at 1/4 bit time to determine the value of
the Manchester bit and clocks the data out at RX on the
following RCLK. The data receiver also generates the
signal used for phase detector comparison to the inter­nal Am7992B V

CO

.

Differential l/O Terminations

The differential input for the Manchester data
(Receive±) is externally terminated by two 40.2-ohm
±1% resistors and one optional common-mode bypass
capacitor. The differential input impedance, Z

lDF

and

the common-mode input, Z

lCM

, are specified so that the
Ethernet specification for cable termination impedance
is met using standard 1% resistor terminators. The Col­lision± differential inputs are terminated in exactly the
same way as the receive inputs (see Figure 6).

Collision Detection

A transceiver detects collisions on the network and
generates a 10 MHz signal at the Collision± inputs. This
collision signal passes through an input stage that de­tects signal levels and pulse duration. When the signal
is detected by the Am7992B, it sets the CLSN line
HIGH. This condition continues for approximately
160ns after the last LOW-to-HlGH transition on
Collision±.

03378I-10

Notes:

1. Connect R1, R2, C1, C2 for 0 differential nontransmit. Connect to ground for logic 1 differential nontransmit.

2. Pin 20 shown for normal device operation.

3. The inclusion of C4 and C5 is necessary to reduce the common-mode loading on certain transceivers that are direct
coupled.

4. C2 reduces the amount of noise from the power supply and crosstalk from RCLK that can be coupled from TSEL through to
the transmit

±

outputs.

Figure 6. External Component Diagram

R

1

C

2

20 pF

R

2

C1680 pF

3 KΩ

100 pF

100 pF

20 MHz

Parallel Mode.

Crystal 50 pF

0.005% Accuracy

V

CC

4700 pF

0.1 µF

4.7 µF

V

CC

0.1 µF

C

5

C

4

0.1 µF

A

B

40.2 Ω 1%

40.2 Ω 1%

40.2 Ω 1%

40.2 Ω 1%

510 Ω

0.1 µF

1
2
3
4
5
6
7
8

9
10
11
12

24
23
22
21
20
19
18
17
16
15
14
13

CLSN
RX
RENA
RCLK
TSEL
GND1
GND2
X1
X2
TX
TCLK
TENA

Collision+
Collision–

Receive+
Receive–

TEST

V

CC1

V

CC2

PF

RF

GND3
Transmit+
Transmit–