PEB2085 SIEMENS [Siemens Semiconductor Group], PEB2085 Datasheet - Page 260

• Manufacturer Part Number: PEB2085
• Description: ISDN SubscribernAccess Controller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

The 1536-kHz clock (TE mode) and the 512-kHz clock (LT-T mode) are phase-locked to the
receive S signal, and derived using the internal DPLL and the 7.68 MHz 100 ppm crystal.
A phase tracking with respect to "S" is performed once in 250 s. As a consequence of this
DPLL tracking, the "high" state of the 1536-kHz clock may be either reduced or extended by
one 7.68-MHz period (duty ratio 2:2 or 4:2 instead of 3:2) once every 250 s. Since the other
signals are derived from this clock (TE mode), the "high" or "low" states may likewise be
reduced or extended by the same amount once every 250 s.
The phase relationships of the clocks are shown in figure 101.
Figure 101
Phase Relationships of ISAC
The timing relationships between the clocks are specified in figure 98 and table 28.
Semiconductor Group
1536
X1 :
768 kHz
512
7.68 MHz
3840 kHz
kHz
kHz
*
*
Synchronous to receive S/T. Duty Ratio 3:2 Normally
®
-S Clock Signals
260
Electrical Characteristics
ITD00876