Specifications

34
3706C–MICRO–2/11
AT89LP3240/6440
generated reset can be extended beyond the power-on period by holding the RST pin low longer
than the time-out.
Figure 7-1. Power-on Reset Sequence (BOD Disabled)
If the Brown-out Detector (BOD) is also enabled, the start-up timer does not begin counting until
after V
DD
reaches the BOD threshold voltage V
BOD
as shown in Figure 7-2. However, if this event
occurs prior to the end of the initialization sequence, the timer must first wait for that sequence to
complete before counting.
Figure 7-2. Power-on Reset Sequence (BOD Enabled)
Note: t
POR
is approximately 143 µs ± 5%.
The start-up timer delay is user-configurable with the Start-up Time User Fuses and depends on
the clock source (Table 7-1). The Start-Up Time fuses also control the length of the start-up time
after a Brown-out Reset or when waking up from Power-down during internally timed mode. The
start-up delay should be selected to provide enough settling time for V
DD
and the selected clock
source. The device operating environment (supply voltage, frequency, temperature, etc.) must
V
DD
RST
Time-out
t
POR
+ t
SUT
t
RHD
V
POR
Internal
Reset
RST
Internal
Reset
V
IH
(RST Tied to V
CC
)
(RST Controlled Externally)
V
POR
V
DD
RST
Time-out
t
POR
t
RHD
V
POR
Internal
Reset
RST
Internal
Reset
V
IH
t
SUT
V
BOD
(RST Tied to V
CC
)
(RST Controlled Externally)