AT90S8515

Manufacturer Part NumberAT90S8515
Description8-bit microcontroller with 8K bytes in-system programmable flash, 2.7-6.0V
ManufacturerATMEL Corporation
AT90S8515 datasheet
 
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Page 24/112:

Number of Watchdog Oscillator Cycles

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Power-on Reset
AT90S8515
24
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 95.
Table 4. Number of Watchdog Oscillator Cycles
FSTRT
Time-out at V
Programmed
0.28 ms
Unprogrammed
16.0 ms
A Power-on Reset (POR) circuit ensures that the device is reset from power-on. As
shown in Figure 23, an internal timer clocked from the Watchdog Timer oscillator pre-
vents the MCU from starting until after a certain period after V
on Threshold Voltage (V
), regardless of the V
POT
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
an external pull-up resistor. By holding the pin low for a period after V
applied, the Power-on Reset period can be extended. Refer to Figure 25 for a timing
example of this.
Figure 24. MCU Start-up, RESET Tied to V
V
POT
VCC
V
RST
RESET
t
TOUT
TIME-OUT
INTERNAL
RESET
Figure 25. MCU Start-up, RESET Controlled Externally
V
POT
VCC
RESET
TIME-OUT
INTERNAL
RESET
= 5V
Number of WDT Cycles
CC
256
16K
has reached the Power-
CC
rise time (see Figure 24). The
CC
CC
.
CC
V
RST
t
TOUT
directly or via
has been
CC
0841G–09/01