MT9042C 데이터 시트보기 (PDF) - Mitel Networks
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MT9042C Datasheet PDF : 28 Pages
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Advance Information
MT9042C
DPLL and the Guard Time Circuit. Control is based
on the logic levels at the control inputs LOS1, LOS2,
RSEL, MS1, MS2 and GTi of the Guard Time Circuit
(See Figure 6).
To
Reference
Select MUX
To TIE
Corrector
Enable
To DPLL
State
Select
RSEL
LOS1
LOS2
Automatic/Manual Control
State Machine
To
and From
Guard Time
Circuit
MS1 MS2
Figure 6 - Automatic/Manual Control State
Machine Block Diagram
All state machine changes occur synchronously on
the rising edge of F8o. See the Controls and Modes
of Operation section for full details on Automatic
Control and Manual Control.
Guard Time Circuit
The GTi pin is used by the Automatic/Manual Control
State Machine in the MT9042C under either Manual
or Automatic control. The logic level at the GTi pin
performs two functions, it enables and disables the
TIE Corrector Circuit (Manual and Automatic), and it
selects which mode change takes place (Automatic
only). See the Applications - Guard Time section.
For both Manual and Automatic control, when
switching from Primary Holdover to Primary Normal,
the TIE Corrector Circuit is enabled when GTi=1, and
disabled when GTi=0.
Under Automatic control and in Primary Normal
Mode, two state changes are possible (not counting
Auto-Holdover). These are state changes to Primary
Holdover or to Secondary Normal. The logic level at
the GTi pin determines which state change occurs.
When GTi=0, the state change is to Primary
Holdover. When GTi=1, the state change is to
Secondary Normal.
Master Clock
The MT9042C can use either a clock or crystal as
the master timing source. For recommended master
timing circuits, see the Applications - Master Clock
section.
Control and Modes of Operation
The MT9042C can operate either in Manual or
Automatic Control. Each control method has three
possible modes of operation, Normal, Holdover and
Freerun.
As shown in Table 3, Mode/Control Select pins MS2
and MS1 select the mode and method of control.
Control RSEL
Input Reference
MANUAL
0
PRI
1
SEC
AUTO
0
State Machine Control
1
Reserved
Table 2 - Input Reference Selection
MS2 MS1 Control
Mode
0
0 MANUAL
NORMAL
0
1 MANUAL
HOLDOVER
1
0 MANUAL
FREERUN
1
1
AUTO State Machine Control
Table 3 - Operating Modes and States
Manual Control
Manual Control should be used when either very
simple MT9042C control is required, or when
complex control is required which is not
accommodated by Automatic Control. For example,
very simple control could include operation in a
system which only requires Normal Mode with
reference switching using only a single input stimulus
(RSEL). Very simple control would require no
external circuitry. Complex control could include a
system which requires state changes between
Normal, Holdover and Freerun Modes based on
numerous input stimuli. Complex control would
require external circuitry, typically a microcontroller.
Under Manual Control, one of the three modes is
selected by mode/control select pins MS2 and MS1.
The active reference input (PRI or SEC) is selected
by the RSEL pin as shown in Table 2. Refer to Table
4 and Figure 7 for details of the state change
sequences.
7
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