21
AT90S/LS2323/2343
1004D–09/01
Note:
1. The Power-on Reset will not work unless the supply voltage has been below V
POT
(falling).
Note:
1. The Power-on Reset will not work unless the supply voltage has been below V
POT
(falling).
Power-on Reset
The AT90S2323/2343 is designed for use in systems where it can operate from the
internal RC oscillator (AT90S/LS2343), on-chip oscillator (AT90S/LS2323), or in appli-
cations where a clock signal is provided by an external clock source. After V
CC
has
reached V
POT
, the device will start after the time t
TOUT
(see Figure 25). If the clock signal
is provided by an external clock source, the clock must not be applied until V
CC
has
reached the minimum voltage defined for the applied frequency.
For AT90S2323, the user can select the start-up time according to typical oscillator
start-up. The number of WDT oscillator cycles used for each time-out is shown in
Table 6. For AT90S2343, the start-up time is one Watchdog cycle only. The frequency
of the Watchdog oscillator is voltage-dependent as shown in “Typical Characteristics” on
page 49.
Table 4.
Reset Characteristics (V
CC
= 5.0V)
Symbol
Parameter
Min
Typ
Max
Units
V
POT
Power-on Reset Threshold Voltage, rising
1.0
1.4
1.8
V
Power-on Reset Threshold Voltage, falling
0.4
0.6
0.8
V
V
RST
RESET Pin Threshold Voltage
0.6 V
CC
V
t
TOUT
Reset Delay Time-out Period AT90S/LS2323
FSTRT Programmed
1.0
1.1
1.2
ms
t
TOUT
Reset Delay Time-out Period AT90S/LS2323
FSTRT Unprogrammed
11.0
16.0
21.0
ms
t
TOUT
Reset Delay Time-out Period AT90S/LS2343
11.0
16.0
21.0
µs
Table 5.
Reset Characteristics (V
CC
= 3.0V)
Symbol
Parameter
Min
Typ
Max
Units
V
POT
Power-on Reset Threshold Voltage, rising
1.0
1.4
1.8
V
Power-on Reset Threshold Voltage, falling
0.4
0.6
0.8
V
V
RST
RESET Pin Threshold Voltage
0.6 V
CC
V
t
TOUT
Reset Delay Time-out Period AT90S/LS2323
FSTRT Programmed
2.0
2.2
2.4
ms
t
TOUT
Reset Delay Time-out Period AT90S/LS2323
FSTRT Unprogrammed
22.0
32.0
42.0
ms
t
TOUT
Reset Delay Time-out Period AT90S/LS2343
22.0
32.0
42.0
µs
Table 6.
Number of Watchdog Oscillator Cycles
FSTRT
Time-out at V
CC
= 5V
Number of WDT Cycles
Programmed
1.1 ms
1K
Unprogrammed
16.0 ms
16K