PRINCIPLES OF OPERATION
Power On Reset
Application of power to the X5043/X5045 activates a
Power On Reset Circuit. This circuit pulls the RESET/
RESET pin active. RESET/RESET prevents the sys-
tem microprocessor from starting to operate with insuf-
ﬁcient voltage or prior to stabilization of the oscillator.
When VCC exceeds the device VTRIP value for 200ms
(nominal) the circuit releases RESET/RESET, allowing
the processor to begin executing code.
Low Voltage Monitoring
During operation, the X5043/X5045 monitors the VCC
level and asserts RESET/RESET if supply voltage falls
below a preset minimum VTRIP. 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 VCC returns and exceeds
VTRIP for 200ms.
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 an active 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
determines the watchdog timer period. The micropro-
cessor can change these watchdog bits. With no
microprocessor action, the watchdog timer control bits
remain unchanged, even during total power failure.
VCC Threshold Reset Procedure
The X5043/X5045 is shipped with a standard VCC
threshold (VTRIP) voltage. This value will not change
over normal operating and storage conditions. How-
ever, in applications where the standard VTRIP is not
exactly right, or if higher precision is needed in the
VTRIP value, the X5043/X5045 threshold may be
adjusted. The procedure is described below, and uses
the application of a high voltage control signal.
Setting the VTRIP Voltage
This procedure is used to set the VTRIP to a higher volt-
age value. For example, if the current VTRIP is 4.4V
and the new VTRIP is 4.6V, this procedure will directly
make the change. If the new setting is to be lower than
the current setting, then it is necessary to reset the trip
point before setting the new value.
To set the new VTRIP voltage, apply the desired VTRIP
threshold voltage to the VCC pin and tie the WP pin to
the programming voltage VP. Then send a WREN com-
mand, followed by a write of Data 00h to address 01h.
CS going HIGH on the write operation initiates the
VTRIP programming sequence. Bring WP LOW to com-
plete the operation.
Note: This operation also writes 00h to array address 01h.
Figure 1. Set VTRIP Level Sequence (VCC = desired VTRIP value.)
WP VPE = 15-18V
0 1 23 4 56 7
REV 1.1.2 5/29/01
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Characteristics subject to change without notice. 3 of 20