CMOS
at 8 kHz to generate T1 (1.544 MHz) clock. For
DPLL #2, the divisions are set at 8 and 256 to
provide the CEPT/ST-BUS clock at 2.048 MHz
synchronized to the falling edge of the input signal (8
kHz). The master clock source is specified to be
12.352 MHz for DPLL #1 and 16.384 MHz for DPLL
#2 over the entire temperature range of operation.
The inputs MS0 to MS3 are used to select the
operating mode of the MT8941B, see Tables 1 to 4.
All the outputs are controlled to the high impedance
condition by their respective enable controls. The
uncommitted NAND gate is available for use in
applications involving Mitel’s MT8976/ MH89760 (T1
Interfaces)
and
MT8979/MH89790
(CEPT
Interfaces).
M
S
0
X
M
S
1
0
Mode of
Operation
NORMAL
MT8941B
Function
Provides the T1 (1.544 MHz) clock
synchronized to the falling edge of
the input frame pulse (F0i).
DPLL #1 divides the CVb input by
193. The divided output is
connected to DPLL #2.
DPLL #1 divides the CVb input by
256. The divided output is
connected to DPLL #2.
0
1
DIVIDE-1
1
Note:
1
DIVIDE-2
X: indicates don’t care
Table 1. Major Modes of DPLL #1
M M
S S
0 1
0
0
Mode of
Operation
NORMAL
Function
Provides CEPT/ST-BUS timing
signals locked to the falling edge of
the 8 kHz input signal at C8Kb.
Modes of Operation
The operation of the MT8941B is categorized into
major modes and minor modes. The major modes
are defined for both DPLLs by the mode select pins
MS0 and MS1. The minor modes are selected by
pins MS2 and MS3 and are applicable only to DPLL
#2. There are no minor modes for DPLL #1.
Major modes of DPLL #1
DPLL #1 can be operated in three major modes as
selected by MS0 and MS1 (Table 1). When MS1 is
LOW, it is in NORMAL mode, which provides a T1
(1.544 MHz) clock signal locked to the falling edge
of the input frame pulse F0i (8 kHz). DPLL #1
requires a master clock input of 12.352 MHz (C12i).
In the second and third major modes (MS1 is HIGH),
DPLL #1 is set to DIVIDE an external 1.544 MHz or
2.048 MHz signal applied at CVb (pin 21). The
division can be set by MS0 to be either 193 (LOW) or
256 (HIGH). In these modes, the 8 kHz output at
C8Kb is connected internally to DPLL #2, which
operates in SINGLE CLOCK mode.
Major modes of DPLL #2
There are four major modes for DPLL #2 selectable
by MS0 and MS1, as shown in Table 2. In all these
modes DPLL #2 provides the CEPT PCM30 timing,
and the ST-BUS clock and framing signals.
In NORMAL mode, DPLL #2 provides the CEPT/ST-
BUS compatible timing signals locked to the falling
edge of the 8 kHz input signal (C8Kb). These
signals are 4.096 MHz (C4o and C4b) and 2.048
MHz (C2o and C2o) clocks, and the 8 kHz frame
pulse (F0b) derived from the 16.384 MHz master
clock. This mode can be the same as the FREE-
RUN mode if the C8Kb pin is tied to V
DD
or V
SS
.
0
1
1
SINGLE
CLOCK-2
1
0
Provides CEPT/ST-BUS timing and
FREE-RUN framing signals with no external
inputs, except the master clock.
SINGLE
CLOCK-1
Provides CEPT/ST-BUS timing
signals locked to the falling edge of
the 8 kHz internal signal provided by
DPLL #1.
Provides CEPT/ST-BUS timing
signals locked to the falling edge of
the 8 kHz internal signal provided by
DPLL #1.
0
1
Table 2. Major Modes of DPLL #2
M
S
2
1
M
S
3
Functional Description
Provides CEPT/ST-BUS 4.096 MHz and 2.048
1 MHz clocks and 8kHz frame pulse depending on
the major mode selected.
Provides CEPT/ST-BUS 4.096 MHz & 2.048 MHz
clocks depending on the major mode selected
1 while F0b acts as an input. However, the input on
F0b has no effect on the operation of DPLL #2
unless it is in FREE-RUN mode.
Overrides the major mode selected and accepts
properly phase related external 4.096 MHz clock
0
and 8 kHz frame pulse to provide the ST-BUS
compatible clock at 2.048 MHz.
Overrides the major mode selected and accepts a
4.096 MHz external clock to provide the ST-BUS
0
clock and frame pulse at 2.048 MHz and 8 kHz,
respectively.
0
1
Table 3. Minor Modes of DPLL #2
In FREE-RUN mode, DPLL #2 generates the stand-
alone CEPT and ST-BUS timing and framing signals
with no external inputs except the master clock set at
16.384 MHz. The DPLL makes no correction in this
configuration and provides the timing signals without
any jitter.
5
MITEL [ MITEL NETWORKS CORPORATION ]
