X5645 XICOR [Xicor Inc.], X5645 Datasheet - Page 3

• Manufacturer Part Number: X5645
• Description: CPU Supervisor with 64Kbit SPI EEPROM
• Manufacturer: XICOR [Xicor Inc.]

X5643/X5645
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
value for 200ms (nominal) the circuit releases RESET/
RESET, allowing the processor to begin executing code.
Low Voltage Monitoring
During operation, the X5643/X5645 monitors the V
level and asserts RESET/RESET if supply voltage falls
below a preset minimum V
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
V
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 watchdog
time out period. The state of two nonvolatile control bits
in the status register determine the watchdog timer
period. The microprocessor can change these watchdog
bits, or they may be “locked” by tying the WP pin LOW
and setting the WPEN bit HIGH.
V
The X5643/X5645 has a standard V
(V
operating and storage conditions. However, in applica-
tions where the standard V
for higher precision in the V
X5645 threshold may be adjusted.
Setting the V
This procedure sets the V
value. For example, if the current V
new V
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.
REV 1.1.1 3/5/01
TRIP
CC
TRIP
Threshold Reset Procedure
for 200ms.
TRIP
) voltage. This value will not change over normal
is 4.6V, this procedure directly makes the
TRIP
Voltage
CC
TRIP
TRIP
exceeds the device V
TRIP
CC
TRIP
. The RESET/RESET
is not exactly right, or
returns and exceeds
to a higher voltage
TRIP
value, the X5643/
is 4.4V and the
CC
threshold
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TRIP
CC
To set the new V
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
to both SCK and SI and pulse CS/WDI LOW then
HIGH. Remove V
Figure 1. Set V
Resetting the V
This procedure sets the V
level. For example, if the current V
V
1.7V. This procedure must be used to set the voltage to
a lower value.
To reset the V
and 5.5V to the V
pin, and the SCK pin HIGH. RESET/RESET and SO
pins are left unconnected. Then apply the programming
voltage V
then HIGH. Remove V
Figure 2. Reset V
TRIP
is reset, the new V
SCK
SCK
SI
CS
SI
CS
P
to the SI pin ONLY and pulse CS/WDI LOW
V
V
V
V
TRIP
P
CC
P
P
TRIP
TRIP
TRIP
P
CC
Characteristics subject to change without notice.
TRIP
voltage, apply a voltage between 2.7
and the sequence is complete.
Voltage
Voltage
P
pin. Tie the CS/WDI pin, the WP
voltage, apply the desired V
Voltage
and the sequence is complete.
TRIP
TRIP
is something less than
to a “native” voltage
TRIP
is 4.4V and the
3 of 19
TRIP
P