am7992b Advanced Micro Devices, am7992b Datasheet - Page 7

• Manufacturer Part Number: am7992b
• Description: Serial Interface Adapter Sia
• Manufacturer: Advanced Micro Devices

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%:
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, X
Resonant Frequency
Error with C
Change in Resonant
Frequency Temperature
with C
Parallel Resonant
Frequency with
C
Motional Crystal
Capacitance, C
ALS Driver or
L
= 50 pF
Equivalent
Figure 3. TTL Clock Driver Circuit for X
L
= 50 pF
2
L
must be left floating (unconnected). An
= 50 pF
1
Min
–50
–40
Nominal
0.022
Limit
20
0
Max
+50
+40
03378I-7
PPM
PPM
MHz
1
Unit
X
pF
1
Am7992B
external clock having the following characteristics
must be used to ensure less than +0.5 ns jitter at
Transmit+ (see the X
waveform diagram and the TTL Clock Driver Circuit
for X
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.
RENA
RCLK
Clock Frequency: 20 MHz 0.01%
Rise/Fall Time (t
X
X
1.5 V input
RX
1
1
1
, Figure 3):
HIGH/LOW Time (t
Falling Edge-to-Falling Edge Jitter: < 0.2 ns at
Manchester
Decoder
Carrier
Detect
Figure 4. Receiver
R
/t
F
1
): <4 ns, monotonic
Driven from External Source
HlGH
/t
LOW
Receiver
Reject
Noise
Filter
): > 20 ns
Data
03378I-8
DI
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