參數(shù)資料
型號: X5645
元件分類: CPU監(jiān)測
英文描述: RTC Module With CPU Supervisor
中文描述: 時鐘模塊CPU監(jiān)控
文件頁數(shù): 3/19頁
文件大小: 312K
代理商: X5645
3
FN8135.1
July 18, 2005
PRINCIPLES OF OPERATION
Power-on Reset
Application of power to the X5643/X5645 activates a
power-on reset circuit. This circuit goes active at about
1V and pulls the RESET/RESET pin active. This signal
prevents the system microprocessor from starting to
operate with insufficient voltage or prior to stabilization
of the oscillator. When V
CC
exceeds the device V
TRIP
value for 200ms (nominal) the circuit releases
RESET/RESET, allowing the processor to begin execut-
ing code.
Low Voltage Monitoring
During operation, the X5643/X5645 monitors the V
CC
level and asserts RESET/RESET if supply voltage falls
below a preset minimum V
TRIP
. The RESET/RESET
signal prevents the microprocessor from operating in a
power fail or brownout condition. The RESET/RESET
signal remains active until the voltage drops below 1V.
It also remains active until V
CC
returns and exceeds
V
TRIP
for 200ms.
Watchdog Timer
The watchdog timer circuit monitors the microprocessor
activity by monitoring the WDI input. The microproces-
sor must toggle the CS/WDI pin periodically to prevent a
RESET/RESET signal. The CS/WDI pin must be toggled
from HIGH to LOW prior to the expiration of the watch-
dog time out period. The state of two nonvolatile con-
trol bits in the status register determine the watchdog
timer period. The microprocessor can change these
watchdog bits, or they may be “l(fā)ocked” by tying the WP
pin LOW and setting the WPEN bit HIGH.
V
CC
Threshold Reset Procedure
The X5643/X5645 has a standard V
CC
threshold
(V
TRIP
) voltage. This value will not change over normal
operating and storage conditions. However, in applica-
tions where the standard V
TRIP
is not exactly right, or
for higher precision in the V
TRIP
value, the
X5643/X5645 threshold may be adjusted.
Setting the V
TRIP
Voltage
This procedure sets the V
TRIP
to a higher voltage
value. For example, if the current V
TRIP
is 4.4V and the
new V
TRIP
is 4.6V, this procedure directly makes the
change. If the new setting is lower than the current set-
ting, then it is necessary to reset the trip point before
setting the new value.
To set the new V
TRIP
voltage, apply the desired V
TRIP
threshold to the Vcc pin and tie the CS/WDI pin and
the WP pin HIGH. RESET/RESET and SO pins are
left unconnected. Then apply the programming voltage
V
P
to both SCK and SI and pulse CS/WDI LOW then
HIGH. Remove V
P
and the sequence is complete.
Figure 1. Set V
TRIP
Voltage
Resetting the V
TRIP
Voltage
This procedure sets the V
TRIP
to a “native” voltage
level. For example, if the current V
TRIP
is 4.4V and the
V
TRIP
is reset, the new V
TRIP
is something less than
1.7V. This procedure must be used to set the voltage
to a lower value.
To reset the V
TRIP
voltage, apply a voltage between 2.7
and 5.5V to the V
CC
pin. Tie the CS/WDI pin, the WP pin,
and the SCK pin HIGH. RESET/RESET and SO pins are
left unconnected. Then apply the programming voltage
V
P
to the SI pin ONLY and pulse CS/WDI LOW then
HIGH. Remove V
P
and the sequence is complete.
Figure 2. Reset V
TRIP
Voltage
SCK
SI
V
P
V
P
CS
SCK
SI
V
CC
V
P
CS
X5643, X5645
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