ISL88813 Intersil Corporation, ISL88813 Datasheet - Page 8

• Manufacturer Part Number: ISL88813
• Description: (ISL88705 - ISL88813) uP Supervisor
• Manufacturer: Intersil Corporation

Manual Reset
The manual-reset input (MR) allows the user to trigger a
reset by using a push-button switch. The MR input is an
active low debounced input. By connecting a push-button
directly from MR to ground, the designer adds manual
system reset capability (see Figure 4). Reset is asserted if
the MR pin is pulled low to less than 100mV for the minimum
MR pulse width or longer while the push-button is closed.
After MR is released, the reset outputs remain asserted for
t
POR
FIGURE 4. CONNECTING A MANUAL RESET PUSH-BUTTON
(200ms) and then released.
V
WDI
WDO
RST
DD
V
1V
TH1
ISL8870X
ISL88705, ISL88706, ISL88707, ISL88708, 8SL88716, ISL88813
20k
MR
8
t
< t
POR
WDT
FIGURE 5. WATCHDOG TIMING DIAGRAM
PB
>t
< t
WDPS
WDT
t
t
WDT
POR
Watchdog Timer
The Watchdog Timer circuit checks microprocessor activity
by monitoring the WDI input pin. The microprocessor must
periodically toggle the WDI pin within t
otherwise the WDO pin goes low (see Figure 5). Internally,
the 1.6s timer is cleared by either a reset or by toggling the
WDI input, which can detect pulses longer than 50ns.
Whenever there is a low-voltage V
low. Unlike the reset outputs, however, WDO does not have
a minimum reset pulse width (t
soon as V
With WDI open or connected to a tristated high impedance
input, the Watchdog Timer is disabled and only pulls low
when V
< t
WDT
DD
DD
< V
t
rises above its voltage trip point (see Figure 5).
RPD
TH1.
POR
DD
). WDO goes high as
condition, WDO goes
WDT
t
POR
(typically 1.6s),
December 6, 2006
FN8092.3