MC145572PB Freescale Semiconductor, MC145572PB Datasheet - Page 35

• Manufacturer Part Number: MC145572PB
• Manufacturer: Freescale Semiconductor

Specifications of MC145572PB

• Number Of Line Interfaces: 1
• Control Interface: HDLC
• Lead Free Status / Rohs Status: Not Compliant

MOTOROLA
3.3.7
Crystal Oscillator Description
In LT mode, an internal PLL synchronizes a voltage controlled 20.48 MHz crystal oscillator to an 8 kHz
reference frequency supplied by the switching equipment. This phase–locked clock assures that the
transmitted 2B1Q signal is synchronized to the frequency reference supplied at the FREQREF pin.
In addition, the very low frequency response (1 Hz) of the internal PLL loop filter limits jitter present
in the frequency reference.
In NT mode, the MC145572 synchronizes its DCL clock output pin to the recovered timing from the
U–interface. This clock is available at 512 kHz, 2.048 MHz, and 2.56 MHz. Frequency adjustments
are also made to the 20.48 MHz oscillator, but it is not precisely locked to the recovered 2B1Q signal
XTAL in and XTAL out : Crystal Input and Crystal Output
A 20.48 MHz pullable crystal is connected between XTAL in and XTAL out to form a voltage–
controlled crystal oscillator in the LT or NT modes. No other external components are required.
See Section H.3 for information on how to characterize the pullable crystal.
ANSI T1.601–1992 requirements. Some ANSI and ETSI applications require a
NT Mode: In MCU/GCI = 1 mode, FREQREF can be enabled as an output when
the MC145572 is configured for NT mode by setting OR8(b4) to a 1. This signal outputs
the internally–generated DCL clock when enabled. Its frequency is programmed by
the DCL frequency bits BR7(b2) and OR7(b4).
GCI Mode: In MCU/GCI = 0 mode, a separate pin, FREF out, provides the synchro-
nized clock and is available for all configurations except for when TxBCLK is enabled.
Use the CLKSEL pin to select between 512 kHz and 2.048 MHz in NT mode.
32 ppm reference.
Figure 3–1. Method to Drive MC145572 with External Clock
Freescale Semiconductor, Inc.
*Required for LT mode only.
For More Information On This Product,
Go to: www.freescale.com
MC145572
+
-
(LT)
MC145572
XTAL out
XTAL in
CAP3V
BUFXTAL
FREQREF
EXTERNAL
20.480000 MHz
CLOCK SOURCE
100 pF DRIVE
*
3–13