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PDF 24C21 Data sheet ( Hoja de datos )
| Número de pieza | 24C21 | |
| Descripción | 2-Wire Serial EEPROM | |
| Fabricantes | ATMELCorporation | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de 24C21 (archivo pdf) en la parte inferior de esta página. Total 13 Páginas | ||
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Features
• 2-Wire Serial Interface
• Schmitt Trigger, Filtered Inputs For Noise Suppression
• DDC1™/ DDC2™ Interface Compliant for Monitor Identification
• Low Voltage Operation
– 2.5 (VCC = 2.5V to 5.5V)
• Internally Organized 128 x 8
• 100 kHz (2.5V) Compatibility
• 8-Byte Page Write Mode
• Write Protection Available
• Self-timed Write Cycle (10 ms max)
• High Reliability
– Endurance: 1 Million Write Cycles
– Data Retention: 100 Years
– ESD Protection: >3000V
• 8-Pin PDIP and JEDEC SOIC Packages
Description
The AT24C21 provides 1024 bits of serial electrically erasable and programmable
read only memory (EEPROM) organized as 128 words of 8 bits each. The device is
optimized for use in applications requiring data storage and serial transmission of con-
figuration and control information. The AT24C21 features two modes of operation:
Transmit-Only Mode and Bidirectional Mode. Upon power-up, the AT24C21 will be in
the Transmit-Only Mode, sending a serial-bit stream of the entire memory contents,
clocked via the VCLK pin. The Bidirectional Mode is selected by a valid high-to-low
transition on the SCL pin and offers byte selectable read/write capability of the entire
memory array. The AT24C21 is available in space saving 8-pin PDIP and 8-pin SOIC
packages.
Pin Configurations
Pin Name
NC
SDA
SCL
VCLK
Function
No Connect
Serial Data
Serial Clock Input
(Bidirectional Mode)
Serial Clock Input
(Transmit-Only Mode)
2-Wire Serial
EEPROM
1K (128 x 8)
AT24C21
2-Wire, 1K
Serial EEPROM
8-Pin PDIP
8-Pin SOIC
Rev. 0405E–07/98
1
1 page  
AT24C21
Functional Description
The AT24C21 has two modes of operation: the Transmit-
Only Mode and the Bidirectional Mode. There is a separate
2-wire protocol to support each mode, each having a sepa-
rate clock input (SCL and VCLK) and both modes sharing a
common Bidirectional data line (SDA). The AT24C21
enters the Transmit-Only Mode upon powering up the
device. In this mode, the device transmits data on the SDA
pin upon a clock signal on the VCLK pin. The device will
remain in the Transmit-Only Mode until a valid high-to-low
transition takes place on the SCL pin. The device will
switch into the Bidirectional Mode when a valid transition
on the SCL pin is recognized. Once the device has transi-
tioned to the Bidirectional Mode, there is no way to return to
the Transmit-Only Mode, except to power down (reset) the
device.
Transmit-Only Mode (DDC1)
The AT24C21 will power up in the Transmit-Only Mode. In
this mode, the device will output one bit of data on the SDA
pin on each rising edge on the VCLK pin. Data is transmit-
ted in 8 bit words with the most significant bit first. Each
Figure 1. Transmit-Only Mode
word is followed by a 9th “don't care” bit which will be in
high impedance state (refer to Figure 1). The AT24C21 will
continuously cycle through the entire memory array in
incremental sequence as long a VCLK is present and no
falling edges on SCL are received. When the maximum
address (7FH) is reached, the output will wrap around to
the zero location (00H) and continue. The Bidirectional
mode clock (SCL) pin must be held high for the device to
remain in the Transmit-Only mode.
Upon power-up, the AT24C21 will not output valid data until
it has been initialized. During initialization, data will not be
available until after the first nine clocks are sent to the
device (refer to Figure 2). The starting address for the
Transmit-Only mode can be determined during initializa-
tion. If the SDA pin is held high during the first eight clocks
(refer to Figure 2), the starting address will be 7FH. If the
SDA pin is low during the first eight clocks, the starting
address will be 00H. During the ninth clock, SDA should be
in high impedance.
Figure 2. Device Initialization for Transmit-Only Mode
5
5 Page 
Figure 9. Sequential Read
(*=Don’t care bits)
AT24C21
11
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet 24C21.PDF ] | |
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