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24C642 View Datasheet(PDF) - Catalyst Semiconductor => Onsemi

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24C642 Datasheet PDF : 12 Pages
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CAT24C321/322/641/642
PIN DESCRIPTIONS
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. In the 24C321/
641, 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
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).
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.
Watchdog Timer
The Watchdog Timer provides an independent protec-
tion for microcontrollers. During a system failure, the
CAT24C321/641 will respond with a reset signal after a
time-out interval of 1.6 seconds for lack of activity.
24CXX1 is designed with the Watchdog Timer feature
on the SDA input. For the 24C321/641, if the
microcontroller does not toggle the SDA 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 SDA.
As long as the reset signal is asserted, the Watchdog
Timer will not count and will stay cleared. 24C322/642
does not feature the Watchdog Timer function.
Figure 1. RESET Output Timing
t
GLITCH
VTH
VRVALID
VCC
tPURST
t RPD
tPURST
RESET
t RPD
RESET
Doc. No. 25083-00 12/98
5
 

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