Datasheet

MAXQ610
16-Bit Microcontroller with Infrared Module
______________________________________________________________________________________ 23
If a reset is caused by a power-fail, the power-fail moni-
tor can be set to one of the following intervals:
• Always on—continuous monitoring
•2
11
nanopower ring oscillator clocks (~256ms)
•2
12
nanopower ring oscillator clocks (~512ms)
•2
13
nanopower ring oscillator clocks (~1.024s)
In the case where the power-fail circuitry is periodically
turned on, the power-fail detection is turned on for two
nanopower ring oscillator cycles. If V
DD
> V
RST
during
detection, V
DD
is monitored for an additional nanopow-
er ring oscillator period. If V
DD
remains above V
RST
for
the third nanopower ring period, the CPU exits the reset
state and resumes normal operation from utility ROM at
8000h after satisfying the crystal warmup period.
If a reset is generated by any other event, such as the
RESET pin being driven low externally or the watchdog
timer, the power-fail, internal regulator, and crystal
remain on during the CPU reset. In these cases, the
CPU exits the reset state in less than 20 crystal cycles
after the reset source is removed.
STATE POWER-FAIL
INTERNAL
REGULATOR
CRYSTAL
OSCILLATOR
SRAM
RETENTION
COMMENTS
A On Off Off — V
DD
< V
POR.
B On On On —
V
POR
< V
DD
< V
RST.
Crystal warmup time, t
XTAL_RDY
.
CPU held in reset.
C On On On —
V
DD
> V
RST
.
CPU normal operation.
D On On On —
Power drop too short.
Power-fail not detected.
E On On On —
V
RST
< V
DD
< V
PFW
.
PFI is set when V
RST
< V
DD
< V
PFW
and maintains
this state for at least t
PFW
, at which time a power-
fail interrupt is generated (if enabled).
CPU continues normal operation.
F
On
(Periodically)
Off Off Yes
V
POR
< V
DD
< V
RST.
Power-fail detected.
CPU goes into reset.
Power-fail monitor turns on periodically.
G On On On —
V
DD
> V
RST.
Crystal warmup time, t
XTAL_RDY
.
CPU resumes normal operation from 8000h.
H
On
(Periodically)
Off Off Yes
V
POR
< V
DD
< V
RST.
Power-fail detected.
CPU goes into reset.
Power-fail monitor is turned on periodically.
I Off Off Off —
V
DD
< V
POR.
Device held in reset.
No operation allowed.
Table 4. Power-Fail Detection States During Normal Operation