WDI: WATCHDOG INPUT
If there is no transition on the WDI for more than 1.6
seconds, the watchdog timer times out.
WP: WRITE PROTECT
If the pin is tied to VCC the entire memory array becomes
Write Protected (READ only). When the pin is tied to VSS
or left floating normal read/write operations are allowed
to the device.
SCL: SERIAL CLOCK
The serial clock input clocks all data transferred into or
out of the device.
RESET/RESET: RESET I/O
These are open drain pins and can be used as reset
trigger inputs. By forcing a reset condition on the pins the
device will initiate and maintain a reset condition for
approximately 200ms. RESET pin must be connected
through a pull-down and RESET pin must be connected
through a pull-up device.
SDA: SERIAL DATA/ADDRESS
The bidirectional serial data/address pin is used to
transfer all data into and out of the device. The SDA pin
is an open drain output and can be wire-ORed with other
open drain or open collector outputs.
Reset Controller Description
The CAT24CXXX provides a precision RESET control-
ler that ensures correct system operation during brown-
out and power up/down conditions. It is configured
with open drain RESET outputs. During power-up, the
RESET outputs remain active until VCC reaches the
VTH threshold and will continue driving the outputs for
approximately 200ms (tPURST) after reaching VTH. After
the tPURST timeout interval, the device will cease to drive
reset outputs. At this point the reset outputs will be pulled
up or down by their respective pull up/pull down devices.
During power-down, the RESET outputs will begin driv-
ing active when VCC falls below VTH. The RESET
outputs will be valid so long as VCC is >1.0V (VRVALID).
The RESET pins are I/Os; therefore, the CAT24CXXX
can act as a signal conditioning circuit for an externally
applied reset. The inputs are level triggered; that is, the
RESET input in the 24CXXX will initiate a reset timeout
after detecting a high and the RESET input in the
24CXXX will initiate a reset timeout after detecting a low.
The Watchdog Timer provides an independent protec-
tion for microcontrollers. During a system failure, the
CAT24CXXX will respond with a reset signal after a
time-out interval of 1.6 seconds for a lack of activity. The
24C323/643 is designed with a WDI input pin for the
Watchdog Timer function. For the 24C323/643, if the
microcontroller does not toggle the WDI input pin within
1.6 seconds, the Watchdog Timer times out. This will
generate a reset condition on reset outputs. The Watch-
dog Timer is cleared by any transition on WDI.
As long as the reset signal is asserted, the Watchdog
Timer will not count and will stay cleared.
Figure 1. RESET Output Timing
Doc. No. 25084-00 12/98