AT90LS4433-4AI datasheet(23/126 Pages) ATMEL

23 / 126 page

AT90S/LS4433

1042H–AVR–04/03

Note:

1. Or external Power-on Reset.

This table shows the Start-up times from Reset. From sleep, only the clock counting part

of the Start-up time is used. The Watchdog Oscillator is used for timing the Real Time

part of the Start-up time. The number WDT Oscillator cycles used for each time-out is

shown in Table 6.

The frequency of the Watchdog Oscillator is voltage dependent, as shown in the Electri-

cal Characteristics section.

Power-on Reset

A Power-on Reset (POR) pulse is generated by an On-chip Detection circuit. The detec-

tion level is nominally 2.2V. The POR is activated whenever V

CC is below the detection

level. The POR circuit can be used to trigger the Start-up Reset, as well as detect a fail-

ure in supply voltage.

The Power-on Reset (POR) circuit ensures that the device is Reset from Power-on.

Reaching the Power-on Reset threshold voltage invokes a delay counter, which deter-

mines the delay, for which the device is kept in RESET after V

CC rise. The Time-out

period of the delay counter is a combination of Internal RC Oscillator cycles and Exter-

nal Oscillator cycles, and it can be defined by the user through the CKSEL Fuses. The

eight different selections for the delay period are presented in Table 5. The RESET sig-

nal is activated again, without any delay, when the V

CC decreases to below detection

level.

Table 5. Reset Delay Selections

CKSEL

[2:0]

Start-up Time,

TOUT at VCC = 2.7V

Start-up Time,

TOUT at VCC = 5.0V

Recommended Usage

000

16 ms + 6 CK

4 ms + 6 CK

External Clock, slowly rising power

001

6 CK

External Clock, BOD enabled(1)

010

256 ms + 16K CK

64 ms + 16K CK

Crystal Oscillator

011

16 ms + 16K CK

4 ms + 16K CK

Crystal Oscillator, fast rising power

100

16K CK

Crystal Oscillator, BOD enabled(1)

101

256 ms + 1K CK

64 ms + 1K CK

Ceramic Resonator

110

16 ms + 1K CK

4 ms + 1K CK

Ceramic Resonator, fast rising power

111

1K CK

Ceramic Resonator, BOD enabled(1)

Table 6. Number of Watchdog Oscillator Cycles

Time-out

Number of Cycles

4.0 ms (at VCC = 5.0V)

64 ms (at V

CC = 5.0V)

64K

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