AM7990 Просмотр технического описания (PDF) - Advanced Micro Devices

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AM7990

Serial Interface Adapter (SIA)

Advanced Micro Devices 

ALS Driver or

Equivalent

X1

03378I-7

Figure 3. TTL Clock Driver Circuit for X1

SIA Oscillator

Specification for External Crystal

When using a crystal to drive the Am7992B oscillator,

the following crystal specification should be used to en-

sure a transmit accuracy of 0.01%:

Resonant Frequency

Error with CL = 50 pF

Change in Resonant

Frequency Temperature

with CL = 50 pF

Parallel Resonant

Frequency with

CL = 50 pF

Motional Crystal

Capacitance, C1

Limit

Min Nominal Max

–50

0

+50

–40

+40

20

0.022

Unit

PPM

PPM

MHz

pF

Some crystal manufacturers have generated crystals

to this specification. One such manufacturer is Reeves-

Hoffman. Their ordering part number for this crystal is

RH#04-20423-312. Another manufacturer is Epson—

Par t #MA 506-200M-50 pF, which is a surface-

mounted crystal.

Specification for External TTL Level

When driving the oscillator from an external clock

source, X2 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 X1 Driven from External Source

waveform diagram and the TTL Clock Driver Circuit

for X1, Figure 3):

s Clock Frequency: 20 MHz ±0.01%

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

s X1 HIGH/LOW Time (tHlGH/tLOW): > 20 ns

s 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 re-

ceiver. Both receivers share common bias networks to

allow operation over an input common mode range of

0 V to 5.5V.

RX

RCLK

RENA

Manchester

Decoder

Data

Receiver

Carrier

Detect

Noise

Reject

Filter

Figure 4. Receiver

DI±

03378I-8

Am7992B

7

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