MT8940 datasheet(6/16 Pages) MITEL

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MT8940 ISO-CMOS

3-32

F0b (refer to Figure 15). Otherwise, the input on pin

F0b will have no bearing on the operation of DPLL

#2, unless it is in FREE-RUN mode as selected by

MS0 and MS1. In FREE-RUN mode, the input on

F0b is treated the same way as the C8Kb input in

NORMAL mode. The frequency of the input signal on

F0b should be 16 kHz for DPLL #2 to provide the ST-

BUS compatible clocks at 4.096 MHz and 2.048

MHz.

When MS2 is HIGH, the F0b pin provides the ST-

BUS frame pulse output locked to the 8kHz internal

or external signal as determined by the other mode

select pins MS0, MS1 and MS3.

Table 4 summarizes the modes of the two DPLLs. It

should be noted that each of the major modes

selected for DPLL #2 can have any of the minor

modes, although some of the combinations are

functionally similar. The required operation of both

DPLL#1 and DPLL#2 must be considered when

determining MS0-MS3.

Table 4. Summary of Modes of Operation - DPLL #1 and #2

Operating Modes

DPLL #1

DPLL #2

0000

NORMAL MODE

Properly phase related External 4.096 MHz

clock and 8 kHz frame pulse provide the ST-

BUS clock at 2.048 MHz.

0001

NORMAL MODE

F0b is an input but has no function in this mode.

0010

NORMAL MODE

External 4.096 MHz provides the ST-BUS clock

and Frame Pulse at 2.048 MHz and 8 kHz,

respectively.

0011

NORMAL MODE:

Provides the T1 (1.544 MHz) clock

synchronized to the falling edge of the

input frame pulse (F0i).

NORMAL MODE:

Provides the CEPT/ST-BUS compatible timing

signals locked to the 8 kHz input signal (C8Kb).

0100

DIVIDE-1 MODE

Same as mode ‘0’.

0101

DIVIDE-1 MODE

SINGLE CLOCK-1 MODE

F0b is an input, but has no function in this

mode.

0110

DIVIDE-1 MODE

Same as mode 2.

0111

DIVIDE-1 MODE:

Divides the CVb input by 193. The divided

output is connected to DPLL #2.

SINGLE CLOCK-1 MODE:

Provides the CEPT/ST-BUS compatible timing

signals locked to the 8 kHz internal signal

provided by DPLL #1.

1000

NORMAL MODE

Same as mode ‘0’.

1001

NORMAL MODE

F0b is an input and DPLL #2 locks on to

it only if it is at 16 kHz to provide the ST-BUS

control signals.

1010

NORMAL MODE

Same as mode 2.

1011

NORMAL MODE

Provides the T1 (1.544 MHz) clock

synchronized to the falling edge of input frame

pulse (F0i).

FREE-RUN MODE:

Provides the ST-BUS timing signals with no

external inputs except the master clock.

1100

DIVIDE-2 MODE

Same as mode ‘0’.

1101

DIVIDE-2 MODE

SINGLE CLOCK-2 MODE:

F0b is an input, but has no function in this

mode.

1110

DIVIDE-2 MODE

Same as mode 2.

1111

DIVIDE-2 MODE:

Divides the CVb input by 256. The divided

output is connected to DPLL#2.

SINGLE CLOCK-2 MODE:

Provides the CEPT/ST-BUS compatible timing

signals locked to the 8 kHz internal signal

provided by DPLL #1.

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