STM802T/S/R STMicroelectronics, STM802T/S/R Datasheet - Page 14

• Manufacturer Part Number: STM802T/S/R
• Description: 3V Supervisor
• Manufacturer: STMicroelectronics

Specifications of STM802T/S/R

• Operating Temperature: –40 °C to 85 °C (industrial grade)

Operation
2
2.1
2.2
2.3
Note:
14/42
Operation
Reset output
The STM690/704/795/802/804/805/806 supervisor asserts a reset signal to the MCU
whenever V
the push-button reset input (MR) is taken low. RST is guaranteed to be a logic low (logic
high for STM804/805) for 0 V < V
battery, RST is guaranteed valid down to V
During power-up, once V
the reset time-out period, t
If V
low for at least the reset time-out period (t
the internal timer clears. The reset timer starts when V
Push-button reset input (STM704/806)
A logic low on MR asserts reset. Reset remains asserted while MR is low, and for t
Figure
it to be left open if not used. This input can be driven with TTL/CMOS-logic levels or with
open-drain/ collector outputs. Connect a normally open momentary switch from MR to GND
to create a manual reset function; external debounce circuitry is not required. If MR is driven
from long cables or the device is used in a noisy environment, connect a 0.1µF capacitor
from MR to GND to provide additional noise immunity. MR may float, or be tied to V
not used.
Watchdog input (NOT available on STM704/795/806)
The watchdog timer can be used to detect an out-of-control MCU. If the MCU does not
toggle the watchdog input (WDI) within t
watchdog timer is cleared by either:
1.
2.
The timer remains cleared and does not count for as long as reset is asserted. As soon as
reset is released, the timer starts counting (see
Input frequency greater than 20 ns (50 MHz) will be filtered.
CC
a reset pulse, or
by toggling WDI (high-to-low or low-to-high), which can detect pulses as short as 50 ns.
If WDI is tied high or low, a reset pulse is triggered every 1.8 s (t
drops below the reset threshold, RST goes low. Each time RST is asserted, it stays
36) after it returns high. The MR input has an internal 40 k
CC
goes below the reset threshold (V
STM690, STM704, STM795, STM802, STM804, STM805, STM806
CC
rec
exceeds the reset threshold an internal timer keeps RST low for
. After this interval RST returns high.
Doc ID 10519 Rev 9
CC
< V
RST
WD
rec
CC
(1.6 s typ), the reset is asserted. The internal
if V
). Any time V
= 1 V.
BAT
Figure
RST
is greater than 1 V. Without a backup
), a watchdog time-out occurs, or when
CC
37).
CC
returns above the reset threshold.
goes below the reset threshold
pull-up resistor, allowing
WD
+ t
rec
).
CC
rec
(see
when