Atmel AT90S1200 Datasheet page 14

Table 3. Reset Characteristics (V
Symbol Parameter
(1)
V Power-On Reset Threshold Voltage (rising)
POT
Power-On Reset Threshold Voltage (falling)
V Pin Threshold Voltage
RST
t Power-On Reset Period
POR
t Reset Delay Time-Out Period (The Time-out
TOUT
period equals 16K WDT cycles. See "Typical
Characteristics" on page 48. for typical WDT
frequency at different voltages).
Notes: 1. The Power-On Reset will not work unless the supply voltage has been below Vpot (falling).
Power-on Reset
A Power-on Reset (POR) circuit ensures that the device is reset from power-on. As shown in Figure 13, an internal timer
clocked from the Watchdog timer oscillator prevents the MCU from starting until after a certain period after V
reached the Power-on Threshold voltage - V
Figure 14. MCU Start-Up, RESET Tied to V
VCC
RESET
TIME-OUT
INTERNAL
RESET
If the build-in start-up delay is sufficient, RESET can be connected to V
holding the RESET pin low for a period after V
Figure 15 for a timing example on this.
AT90S1200
14
= 5.0V)
CC
, regardless of the V
POT
.
CC
V
POT
V
RST
t
TOUT
has been applied, the Power-on Reset period can be extended. Refer to
CC
Min Typ
0.8 1.2
0.2 0.4
- -
2 3
11 16
rise time (see Figure 14).
CC
directly or via an external pull-up resistor. By
CC
Max Units
1.6 V
0.6 V
0.85V V
CC
4 ms
21 ms
has
CC