ASM813LCPA ALSC [Alliance Semiconductor Corporation], ASM813LCPA Datasheet - Page 4

• Manufacturer Part Number: ASM813LCPA
• Description: Low Power UP Supervisor Circuits
• Manufacturer: ALSC [Alliance Semiconductor Corporation]

rev 1.2
July 2004
Detailed Description
A
microcontroller to start in a known state. ASM70X and
ASM813L assert reset to prevent code execution errors
during power-up, power-down and brown-out conditions.
RESET/RESET Timing
The RESET/RESET signals are designed to start a µP/µC in
a known state or return the system to a known state.
The ASM707/708 have two reset outputs, one active-HIGH
RESET and one active-LOW RESET output. The ASM813L
has only an active-HIGH output. RESET is simply the
complement of RESET.
RESET is guaranteed to be LOW with V
During a power-up sequence, RESET remains low until the
supply rises above the threshold level, either 4.65V or 4.40V.
RESET goes high approximately 200ms after crossing the
threshold.
During power-down, RESET goes LOW as V
the threshold level and is guaranteed to be under 0.4V with
V
In a brownout situation where V
level, RESET pulses low. If a brownout occurs during an
already initiated reset, the pulse will continue for a minimum
of 140ms.
Power Failure Detection With Auxiliary Comparator
All devices have an auxiliary comparator with 1.25V trip point
and uncommitted output (PFO) and noninverting input (PFI).
This comparator can be used as a supply voltage monitor
with an external resistor voltage divider. The attenuated
voltage at PFI should be set just below the 1.25 threshold. As
the supply level falls, PFI is reduced causing the PFO output
to transit LOW. Normally PFO interrupts the processor so the
system can be shut down in a controlled manner.
CC
proper
above 1.2V.
reset
input
enables
CC
Notice: The information in this document is subject to change without notice
falls below the threshold
a
microprocessor
Low Power µP Supervisor Circuits
CC
CC
above 1.2V.
falls below
/
Manual Reset (MR)
The active-LOW manual reset input is pulled high by a 250µA
pull-up current and can be driven low by CMOS/TTL logic or
a mechanical switch to ground. An external debounce circuit
is unnecessary since the 140ms minimum reset time will
debounce mechanical pushbutton switches.
By connecting the watchdog output (WDO) and MR, a
watchdog timeout forces RESET to be generated. The
ASM813L should be used when an active-HIGH RESET is
required.
Watchdog Timer
The watchdog timer available on the ASM705/706/813L
monitors µP/µC activity. An output line on the processor is
used to toggle the WDI line. If this line is not toggled within
1.6 seconds, the internal timer puts the watchdog output,
WDO, into a LOW state. WDO will remain LOW until a toggle
is detected at WDI.
If WDI is floated or connected to a three-stated circuit, the
watchdog function is disabled, meaning, it is cleared and not
counting. The watchdog timer is also disabled if RESET is
asserted. When RESET becomes inactive and the WDI input
sees a high or low transition as short as 50ns, the watchdog
timer will begin a 1.6 second countdown. Additional
Figure 1: WDI Three-state operation
RESET
V
WDO
MR
CC
5V
0V
5V
0V
5V
0V
5V
0V
ASM705 / 706 / 707 / 708
V
RT
MR externally
set low
t
RS
ASM813L
t
MD
t
t
RS
MR
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