X5163 Datasheet, PDF (3/21 Pages) Xicor Inc. – CPU Supervisor with 16Kbit SPI EEPROM

X5163/X5165 – Preliminary Information
PRINCIPLES OF OPERATION
Power On Reset
Application of power to the X5163/X5165 activates a
Power On Reset Circuit. This circuit goes active at 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 executing code.
Low Voltage Monitoring
During operation, the X5163/X5165 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 microproces-
sor activity by monitoring the WDI input. The micropro-
cessor 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 expira-
tion of the watchdog time out period. The state of two
nonvolatile control bits in the Status Register deter-
mine 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_CC Threshold Reset Procedure
The X5163/X5165 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 X5163/
X5165 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 V_CC pin and tie the CS/WDI pin and
the WP pin HIGH. RESET and SO pins are left uncon-
nected. 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
CS
V_P
SCK
V_P
SI
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 and SO
pins are left unconnected. Then apply the program-
ming 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
CS
SCK ^VCC
V_P
SI
REV 1.1 3/5/01
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Characteristics subject to change without notice. 3 of 21