Atmel AT90S2313 User Manual

AT90S2313
21
Notes: 1. The Power-On Reset will not work unless the supply voltage has been below Vpot (falling).
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 4. The frequency of the watchdog oscillator is voltage dependent as shown in “Typical
characteristics” on page 71.
Power-On Reset
A Power-On Reset (POR) circuit ensures that the device is reset from power-on. As shown in Figure 23, an internal timer is
clocked from the Watchdog timer. This timer prevents the MCU from starting until after a certain period after V
CC
has
reached the Power-On Threshold voltage - V
POT
(see Figure 24). The FSTRT fuse bit in the Flash can be programmed to
give a shorter start-up time if a ceramic resonator or any other fast-start oscillator is used to clock the MCU.
If the built-in start-up delay is sufficient, RESET
can be connected to V
CC
directly or via an external pull-up resistor. By
holding the RESET
pin low for a period after V
CC
has been applied, the Power-On Reset period can be extended. Refer to
Figure 25 for a timing example on this.
Figure 24. MCU Start-Up, RESET
Tied to V
CC
.
Table 3. Reset Characteristics (V
CC
= 5.0V)
Symbol Parameter Min Typ Max Units
V
POT
(1)
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
-0.85V
CC
V
t
TOUT
Reset Delay Time-Out Period
FSTRT Unprogrammed
11 16 21 ms
t
TOUT
Reset Delay Time-Out Period
FSTRT Programmed
1.0 1.1 1.2 ms
Table 4. Number of Watchdog Oscillator Cycles
FSTRT Time-out at V
CC
= 5V Number of WDT cycles
Programmed 1.1ms 1K
Unprogrammed 16.0ms 16K
VCC
RESET
TIME-OUT
INTERNAL
RESET
t
TOUT
V
POT
V
RST

Atmel AT90S2313 Specifications

General

Brand	Atmel
Model	AT90S2313
Category	Microcontrollers
Language	English