1996 Microchip Technology Inc.

Preliminary

DS21160B-page 1

FEATURES

• Single supply with operation down to 2.5V
• Completely implements DDC1



/DDC2




interface for monitor identification, including recov-
ery to DDC1
• Pin and function compatible with 24LC21
• Low power CMOS technology
- 1 mA typical active current
- 10

m

A standby current typical at 5.5V
• 2-wire serial interface bus, I

2

C



compatible
• 100 kHz (2.5V) and 400 kHz (5V) compatibility
• Self-timed write cycle (including auto-erase)
• Page-write buffer for up to eight bytes
• 10,000,000 erase/write cycles guaranteed
• Data retention > 200 years
• ESD Protection > 4000V
• 8-pin PDIP and SOIC package
• Available for extended temperature ranges

DESCRIPTION

The Microchip Technology Inc. 24LC21A is a 128 x 8-
bit dual-mode Electrically Erasable PROM. This device
is designed for use in applications requiring storage
and serial transmission of configuration and control
information. Two modes of operation have been imple-
mented: Transmit-Only Mode and Bi-directional Mode.
Upon power-up, the device will be in the Transmit-Only
Mode, sending a serial bit stream of the memory array
from 00h to 7Fh, clocked by the VCLK pin. A valid high
to low transition on the SCL pin will cause the device to
enter the transition mode, and look for a valid control
byte on the I

2

C bus. If it detects a valid control byte from
the master, it will switch into Bi-directional Mode, with
byte selectable read/write capability of the memory
array using SCL. If no control byte is received, the
device will revert to the Transmit-Only Mode after it
receives 128 consecutive VCLK pulses while the SCL
pin is idle. The 24LC21A is available in a standard 8-pin
PDIP and SOIC package in both commercial and
industrial temperature ranges.
- Commercial (C): 0



C to +70



C
- Industrial (I): -40



C to +85



C

PACKAGE TYPES
BLOCK DIAGRAM
PDIP
SOIC
24LC21A
NC
NC
NC
VSS
1
2
3
4
8
7
6
5
VCC
VCLK
SCL
SDA
24LC21A
NC
NC
NC
VSS
1
2
3
4
8
7
6
5
VCC
VCLK
SCL
SDA
HV GENERATOR
EEPROM
ARRAY
PAGE LATCHES
YDEC
XDEC
SENSE AMP
R/W CONTROL
MEMORY
CONTROL
LOGIC
I/O
CONTROL
LOGIC
SDA SCL
VCC
VSS
VCLK

24LC21A

1K 2.5V Dual Mode I

2

C



Serial EEPROM

DDC is a trademark of the Video Electronics Standards Association.
I

2

C is a trademark of Philips Corporation.

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