T8207 Datasheet, PDF (143/158 Pages) Agere Systems – ATM Interconnect

Advance Data Sheet
September 2001
CelXpres T8207
ATM Interconnect
18 Electrical Requirements and Characteristics
18.1 Crystal Information
The CelXpres T8207 device requires a crystal or external clock source. The crystal may have a frequency from
5 MHz to 40 MHz and is connected between xtalin and xtalout. External 5% capacitors must be connected from
xtalin and xtalout to VSS. The value of the external capacitors is determined from the crystal data sheet using the
crystal specification requirements shown below.
Table 130. Crystal Specifications
Parameter
Frequency
Oscillation Mode
Effective Series Resistance
Frequency Tolerance and Stability
Value
5 MHz to 40 MHz
Fundamental parallel resonant
See Figure 20 below
5%
0
XTALIN
C1
XTALOUT
CRYSTAL
C2
−200
−400
−600
50p_pF
= C1
= C2
2200p pF
= C1
= C2
−800
−1000
0
10₁p_{0 pF}
= C1
= C2
10 20 30 40 50 60
FREQUENCY (MHZ_z)
Figure 19. Crystal
Figure 20. Negative Resistance Plot
The xtalin input may be driven by an external clock instead of a crystal. The frequency of the external source may
be 5 MHz to 50 MHz. The external clock must meet the requirements shown below.
Table 131. External Clock Requirements
Parameter
Frequency
Maximum Rise or Fall Time
Duty Cycle
Min
5 MHz
—
40%
Max
50 MHz
5 ns
60%
The frequency of the T8207’s main clock (mclk) is derived from the clock at the xtalin input (pclk). See Section 5,
PLL Configuration, for more information on these clocks.
Agere Systems Inc.
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