MT9042CP1 Zarlink Semiconductor, Inc., MT9042CP1 Datasheet - Page 7

• Manufacturer Part Number: MT9042CP1
• Description: PLL, Dual Reference Frequency Selectable Digital PLL with Multiple Clock Outputs
• Manufacturer: Zarlink Semiconductor, Inc.

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).
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.
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.
RSEL
LOS1
LOS2
Figure 6 - Automatic/Manual Control State
Select MUX
Reference
To
When GTi=1, the state change is to
Automatic/Manual Control
MS1
Machine Block Diagram
State Machine
MS2
Corrector
Enable
To TIE
To DPLL
Select
State
Guard Time
and From
Circuit
To
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.
Manual Control
Manual Control should be used when either very
simple MT9042C control is required, or when
complex
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).
external circuitry. Complex control could include a
system which requires state changes between
Normal, Holdover and Freerun Modes based on
numerous input stimuli.
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
sequences.
MS2
MANUAL
Control
0
0
1
1
AUTO
and Figure 7 for details of the state change
Table 3 - Operating Modes and States
MS1
Table 2 - Input Reference Selection
0
1
0
1
Very simple control would require no
control
RSEL
MANUAL
MANUAL
MANUAL
Control
AUTO
0
1
0
1
is
required
State Machine Control
Complex control would
State Machine Control
Input Reference
Reserved
HOLDOVER
FREERUN
NORMAL
MT9042C
SEC
which
PRI
Mode
is
not
7