NSAM266SA Datasheet, PDF (7/52 Pages) National Semiconductor (TI) – NSAM266SA CompactSPEECHTM Digital Speech Processor with Serial Flash Interface

1 0 Hardware (Continued)
1 3 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
1 3 1 Resetting
The RESET pin is used to reset the CompactSPEECH proc-
essor
On application of power RESET must be held low for at
least t_pwr after V_CC 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 t_RST 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 V_ENVh
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
TL EE 12584 – 5
FIGURE 1-3 Recommended Power-On Reset Circuit
1 3 2 Clocking
The CompactSPEECH provides an internal oscIllator that
interacts with an external clock source through the X1 and
X2 CLKIN 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 1 4 2
TL EE 12584 – 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
TL EE 12584 – 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
X2 CLKIN 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
Resonance Frequency 40 96 MHz
Third Overtone
Parallel
Type
AT-Cut
Crystal ^{Maximum Serial}
Resonator ^Resistance
Maximum Shunt
Capacitance
50X
NA
7 pF
Maximum Load
Capacitance
12 pF
Resistor R1
10 MX
5%
Capacitor C1
1000 pF 20%
Inductor L
3 9 mH 10%
7
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