AM79C978A AMD [Advanced Micro Devices], AM79C978A Datasheet - Page 27

• Manufacturer Part Number: AM79C978A
• Description: Single-Chip 1/10 Mbps PCI Home Networking Controller
• Manufacturer: AMD [Advanced Micro Devices]

HomePNA PHY Network Interface
HRTXRXP/HRTXRXN
Serial Receive Data
These pins accept the receive input data from the mag-
netics module and carry the transmit output data. A
100-W resistor should be placed between these pins.
Clock Interface
XCLK/XTAL
External Clock/Crystal Select
When HIGH, an external 60-MHz clock source is se-
lected bypassing the crystal circuit and clock trippler.
When LOW, a 20-MHz crystal is used instead. The
following table illustrates how this pin works.
XTAL1
Crystal Oscillator In
The internal clock generator utilizes either a 20-MHz
crystal that is attached to pins XTAL1 and XTAL2 or a
60-MHz clock source connected to XTAL1. This pin is
not 5 V tolerant, and the 60 MHz clock source should
be from a 3.3 V source, not a 5 V clock source.
XTAL2
Crystal Oscillator Out
The internal clock generator utilizes either a 20-MHz
crystal that is attached to pins XTAL1 and XTAL2 or a
60-MHz clock source connected to XTAL1.
External Crystal Characteristics
When using a crystal to drive the oscillator, the fol-
lowing crystal specification in Table 3 may be used to
ensure less than ±0.5 ns jitter at DO±.
XTAL1
XTAL1
Input Pin
Table 2. External Clock/Crystal Select
Don’t Care
Output
XTAL2
Pin
XCLK/XTAL
0
1
60-MHz Oscillator/
20-MHz Crystal
Input/Output
Clock Source
External CLK
Source
Input
Output
Input
Am79C978A
Note: *Requires trimming specification; not trimmed is
50 PPM total.
Power Supply
VDDB
I/O Buffer Power (4 Pins)
These pins are the power supply pins that are used by
the input/output buffer drivers. All VDDB pins must be
connected to a +3.3 V supply.
VDD_PCI
PCI I/O Buffer Power (9 Pins)
These pins are the power supply pins that are used
by the PCI input/output buffer drivers (except PME
driver). All VDD_PCI pins must be connected to a
+3.3 V supply.
VSSB
I/O Buffer Ground (15 Pins)
These pins are the ground pins that are used by the
input/output buffer drivers.
VDD
Digital Power (7 Pins)
These pins are the power supply pins that are used
by the internal digital circuitry. All VDD pins must be
connected to a +3.3 V supply.
VSS
Digital Ground (7 Pins)
There are seven ground pins that are used by the internal
digital circuitry.
1. Parallel Resonant
Frequency
2. Resonant Frequency Error
3. Change in Resonant
Frequency With Respect To
Temperature (0-70°C)*
4. Crystal Load Capacitance
5. Motional Crystal
Capacitance (C1)
6. Internal Equivalent Series
Resistance
7. Shunt Capacitance
Table 3. Crystal Characteristics
Parameter
Min
-50
-40
15
0.022
Nom Max Units
20
18
+3.3 V Power
+3.3 V Power
+3.3 V Power
+50
+40
33
50
7
Ground
Ground
PPM
PPM
MHz
ohm
pF
pF
pF
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