MT9044AP1 Zarlink Semiconductor, Inc., MT9044AP1 Datasheet - Page 22

• Manufacturer Part Number: MT9044AP1
• Description: Framer: Framer Circuit: T1/E1/OC3 System Synchronizer
• Manufacturer: Zarlink Semiconductor, Inc.

MT9044
Data Sheet
Reset Circuit
A simple power up reset circuit with about a 50us reset low time is shown in Figure 14. Resistor R
is for protection
P
only and limits current into the RST pin during power down conditions. The reset low time is not critical but should
be greater than 300ns.
MT9044
+5V
R
10kΩ
RST
R
P
1kΩ
C
10nF
Figure 14 - Power-Up Reset Circuit
Dual T1 Reference Sources with MT9044 in Automatic Control
For systems requiring simple state machine control, the application circuit shown in Figure 15 using Automatic
Control may be used.
In this circuit, the MT9044 is operating Automatically, using a Guard Time Circuit, and the LOS1 and LOS2 inputs to
determine all mode changes. Since the Guard Time Circuit is set to about 1s, all line interruptions (LOS1=1) less
than 1s will cause the MT9044 to go from Primary Normal Mode to Holdover Mode and not switch references. For
line interruptions greater than 1s, the MT9044 will switch Modes from Holdover to Secondary Normal, provided that
the secondary signal is valid (LOS2=0). After receiving a good primary signal (LOS1=0), the MT9044 will switch
back to Primary Normal Mode For complete Automatic Control state machine details, refer to Table 5 for the State
Table, and Figure 8 for the State Diagram.
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Zarlink Semiconductor Inc.