NSAM266SAASLASHV datasheet(7/52 Pages) NSC

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10 Hardware (Continued)

13 FUNCTIONAL DESCRIPTION

This section provides details of the functional characteris-

tics of the CompactSPEECH processor It is divided into the

following sections

Resetting

Clocking

Power-down Mode

Power and Grounding

Memory Interface

Codec Interface

131 Resetting

The RESET pin is used to reset the CompactSPEECH proc-

essor

On application of power RESET must be held low for at

least tpwr after VCC is stable This ensures that all on-chip

voltages are completely stable before operation Whenever

RESET is applied it must also remain active for not less

than tRST During this period and for 100 ms after the TST

signal must be high This can be done with a pull-up resistor

on the TST pin

The value of MWRDY is undefined during the reset period

and for 100 ms after The microcontroller should either wait

before polling the signal for the first time or the signal

should be pulled high during this period

Upon reset the ENV0 signal is sampled to determine the

operating environment During reset the EMCS ENV0 pin is

used for the ENV0 input signals An internal pull-up resistor

sets ENV0 to 1

After reset the same pin is used for EMCS

System Load on ENV0

For any load on the ENV0 pin the voltage should not drop

below VENVh

If the load on the ENV0 pin causes the current to exceed

10 mA use an external pull-up resistor to keep the pin at 1

Figure 1-3 shows a recommended circuit for generating a

reset signal when the power is turned on

TLEE12584 – 5

FIGURE 1-3 Recommended Power-On Reset Circuit

132 Clocking

The CompactSPEECH provides an internal oscIllator that

interacts with an external clock source through the X1 and

X2CLKIN pins Either an external single-phase clock sig-

nal or a crystal oscillator may be used as the clock source

External Single-Phase Clock Signal

If an external single-phase clock source is used it should be

connected to the CLKIN signal as shown in

Figure 1-4 and

should conform to the voltage-level requirements for CLKIN

stated in Section 142

TLEE12584 – 6

FIGURE 1-4 External Clock Source

Crystal Oscillator

A crystal oscillator is connected to the on-chip oscillator

circuit via the X1 and X2 signals as shown in

Figure 1-5

TLEE12584 – 7

FIGURE 1-5 Connections for an

External Crystal Oscillator

Keep stray capacitance and inductance in the oscillator cir-

cuit as low as possible The crystal resonator and the ex-

ternal components should be as close to the X1 and

X2CLKIN pins as possible to keep the trace lengths in the

printed circuit to an absolute minimum

You can use crystal resonators with maximum load capaci-

tance of 20 pF although the oscillation frequency may differ

from the crystal’s specified value

Table 1-2 lists the components in the crystal oscillator cir-

cuit

TABLE 1-2 Crystal Oscillator Component List

Component

Parameters

Values

Tolerance

Resonator

Crystal

Resonance Frequency 4096 MHz

Third Overtone

Parallel

Type

AT-Cut

Maximum Serial

50X

Resistance

Maximum Shunt

7pF

Capacitance

Maximum Load

12 pF

Capacitance

Resistor R1

10 MX

Capacitor C1

1000 pF

20%

Inductor L

39 mH

10%

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