Advanced
CAT24CXX1/XX2
PIN DESCRIPTIONS
WP: WRITE PROTECT
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 driving active when VCC falls below VTH. The
RESET outputs will be valid so long as VCC is >1.0V
(VRVALID).
If the pin is tied to VCC the entire memory array becomes
WriteProtected(READonly). WhenthepinistiedtoVSS
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
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
24CXXXwillinitiatearesettimeoutafterdetectingalow.
These are open drain pins and can be used as reset
triggerinputs. Byforcingaresetconditiononthepinsthe
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.
Watchdog Timer
SDA: SERIAL DATA/ADDRESS
The Watchdog Timer provides an independent protec-
tion for microcontrollers. During a system failure, the
CAT24CXX1willrespondwitharesetsignalafteratime-
out interval of 1.6 seconds for lack of activity. 24CXX1
isdesignedwiththeWatchdogTimerfeatureontheSDA
input. For the 24CXX1, if the microcontroller does not
toggle the SDA input pin within 1.6 seconds the Watch-
dog Timer times out. This will generate a reset condition
onresetoutputs. The WatchdogTimerisclearedbyany
transition on SDA.
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
opendrainoropencollectoroutputs. Inthe24CXX1, the
SDA line is also used as the Watchdog Timer Monitor.
DEVICE OPERATION
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
As long as the reset signal is asserted, the Watchdog
Timer will not count and will stay cleared. 24CXX2 does
not feature the Watchdog Timer function.
Figure 1. RESET Output Timing
tGLITCH
VTH
V
RVALID
VCC
tRPD
tPURST
tPURST
RESET
tRPD
RESET
Doc. No. 25079-00 1/98 M-1
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