PRINCIPLES OF OPERATION
Application of power to the X5323/X5325 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. As long as RESET/RESET pin is
active, the device will not respond to any Read/Write
instruction. When VCC exceeds the device VTRIP value
for 200ms (nominal) the circuit releases
RESET/RESET, allowing the processor to begin exe-
Low Voltage Monitoring
During operation, the X5323/X5325 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 microprocessor
activity by monitoring the WDI input. The microprocessor
must toggle the CS/WDI pin periodically to prevent a
RESET/RESET signal. The CS/WDI pin must be tog-
gled 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 watch-
dog 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.
VCC Threshold Reset Procedure
The X5323/X5325 has a standard VCC threshold
(VTRIP) voltage. This value will not change over normal
operating and storage conditions. However, in applica-
tions where the standard VTRIP is not exactly right, or
for higher precision in the VTRIP value, the
X5323/X5325 threshold may be adjusted.
Setting the VTRIP Voltage
This procedure sets the VTRIP to a higher voltage
value. For example, if the current VTRIP is 4.4V and
the new VTRIP is 4.6V, this procedure directly makes
the change. If the new setting is 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 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
VP to both SCK and SI and pulse CS/WDI LOW then
HIGH. Remove VP and the sequence is complete.
Figure 1. Set VTRIP Voltage
Resetting the VTRIP Voltage
This procedure sets the VTRIP to a “native” voltage
level. For example, if the current VTRIP is 4.4V and the
VTRIP is reset, the new VTRIP is something less than
1.7V. This procedure must be used to set the voltage
to a lower value.
To reset the VTRIP voltage, apply a voltage between
2.7 and 5.5V to the VCC 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 pro-
gramming voltage VP to the SI pin ONLY and pulse
CS/WDI LOW then HIGH. Remove VP and the
sequence is complete.
Figure 2. Reset VTRIP Voltage
October 27, 2005