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AT24C21
Features
* * * * * * * * * *
2-Wire Serial Interface DDC1TM/ DDC2TM Interface Compliant for Monitor Identification Low Voltage and Standard Voltage Operation 2.5 (VCC = 2.5V to 5.5V) Internally Organized 128 x 8 100 kHz (2.5V) and 400 kHz (5V) Compatibility 8-Byte Page Write Mode Write Protection Available Self-timed Write Cycle (10 ms max) High Reliability Endurance: 1 Million Cycles Data Retention: 100 Years 8-Pin PDIP and JEDEC SOIC Packages
2-Wire Serial CMOS E2PROM
1K (128 x 8)
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 configuration and control information. The AT24C21 features two modes of operation: Transmit-Only Mode and Bi-Directional 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 Bi-Directional 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 (Bi-Directional Mode) Serial Clock Input (Transmit-Only Mode)
AT24C21
8-Pin PDIP
8-Pin SOIC
0405D
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Absolute Maximum Ratings*
Operating Temperature................... -55C to +125C Storage Temperature...................... -65C to +150C Voltage on Any Pin with Respect to Ground ..................... -0.1V to +7.0V Maximum Operating Voltage ........................... 6.25V DC Output Current ......................................... 5.0 mA
*NOTICE: Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
Block Diagram
Pin Description
SERIAL CLOCK (SCL): The SCL input is used to positive edge clock data into each E2PROM device and negative edge clock data out of each device. SERIAL DATA (SDA): The SDA pin is bidirectional for serial data transfer. This pin is open-drain driven and may be wire-ORed with any number of other open drain or open collector devices.
SERIAL CLOCK (VCLK): Upon power-up, the device is in the Transmit-Only mode and will transmit the entire memory contents via the SDA pin with positive signals on the VCLK pin.
Memory Organization
AT24C21, 1K SERIAL E2PROM: Internally organized with 128 pages of one byte each. The 1K requires a 7 bit data word address for random word addressing.
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AT24C21
AT24C21
DC Characteristics
Applicable over recommended operating range from: TAI = -40C to +85C, TAC = 0C to +70C, VCC = +2.5V to +5.5V (unless otherwise noted). Symbol Parameter VCC ICC ICC ISB ILI ILO VIL Supply Voltage Supply Current VCC = 5.0V Supply Current VCC = 5.0V Standby Current VCC = 2.5V VCC = 5.0V Input Leakage Current Output Leakage Current Input Low Level
(1)
Test Condition READ at 100 kHz WRITE at 100 kHz VIN = VCC or VSS VIN = VCC or VSS VIN = VCC or VSS VOUT = VCC or VSS VCC 2.7V VCC < 2.7V
Min 2.5
Typ 0.4 2.0 3.0 12.0 0.10 0.05
Max 5.5 1.0 3.0 4.0 30.0 1.0 1.0 VCC x 0.3 0.8 0.2 x VCC
Units V mA mA A A A A V V V V V V
SCL, SDA Pin
Input Low Level VCLK Pin VIH VOL
Note:
Input High Level
(1)
SCL, SDA Pin IOL = 2.1 mA
VCC x 0.7 2.0
VCC + 0.5 0.40
Input High Level VCLK Pin Output Low Level VCC = 3.0V
1. VIL min and VIH max are for reference only and not tested.
Pin Capacitance (1)
Applicable over recommended operating range from TA = 25C, f = 1.0 MHz, VCC = +1.8V. Symbol CI/O CIN
Note:
Test Condition Input/Output Capacitance (SDA) Input Capacitance (A0, A1, A2, SCL, VCLK)
Max 8 6
Units pF pF
Conditions VI/O = 0V VIN = 0V
1. This parameter is characterized and is not 100% tested.
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Transmit-Only Mode
2.5-volt Symbol TVAA TVHIGH TVLOW TVHZ TVPU Parameter Output valid from VCLK VCLK high-time VCLK low-time Mode transition time Transmit-Only power-up time 0 4.0 4.7 500 0 Min Max 500 .6 1.3 500 5.0-volt Min Max 500 Units ns s s ns ns
AC Characteristics
Applicable over recommended operating range from TA = -40C to +85C, VCC = +2.5V to +5.5V CL = 1 TTL Gate and 100 pF (unless otherwise noted). Symbol fSCL tLOW tHIGH tI tAA tBUF tHD.STA tSU.STA tHD.DAT tSU.DAT tR tF tSU.STO tDH tWR
Note:
Parameter Min Clock Frequency, SCL Clock Pulse Width Low Clock Pulse Width High Noise Suppression Time (1) (SDA and SCL pins) Clock Low to Data Out Valid Time the bus must be free before a new transmission can start Start Hold Time Start Set-up Time Data In Hold Time Data In Set-up Time Inputs Rise Time Inputs Fall Time
(1) (1)
2.5-volt Max 100 Min 0 1.3 0.6 NA 0.1 4.7 4.0 4.7 0 250 1.0 300 4.0 100 10 0.6 50 3.5 0.1 1.3 0.6 0.6 0 100 0 4.7 4.0
5.0-volt Max 400 Units kHz s s 50 0.9 ns s s s s s ns 0.3 300 s ns s ns 10 ms
Stop Set-up Time Data Out Hold Time Write Cycle Time
1. This parameter is characterized and is not 100% tested.
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AT24C21
AT24C21
Functional Description
The AT24C21 has two modes of operation: the TransmitOnly Mode and the Bi-Directional Mode. There is a separate 2-wire protocol to support each mode, each having a separate clock input (SCL and VCLK) and both modes sharing a common bi-directional 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 Bi-Directional Mode when a valid transition on the SCL pin is recognized. Once the device has transitioned to the Bi-Directional 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 transmitted in 8 bit words with the most significant bit first. Each 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 ouput will wrap around to the zero location (00H) and continue. The Bi-Directional 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 initialization. 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 1. Transmit-Only Mode
Figure 2. Device Initialization for Transmit-Only Mode
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Bi-Directional Mode (DDC2)
This mode supports a 2-wire, bi-directional data transmission protocol. The AT24C21 can be switched into the BiDirectional Mode by issuing a valid high to low transition on the SCL pin (refer to Figure 3). After the device is in the Bi-Directional Mode, all inputs to the VCLK pin are ignored, except when a logic high is required to enable write capability. All byte and page writes and byte and sequential reads are supported in this mode. ACKNOWLEDGE: All addresses and data words are serially transmitted to and from the E2PROM in 8 bit words. The E2PROM sends a zero to acknowledge that it has received each word. This happens during the ninth clock cycle.
Device Addressing
The AT24C21 requires an 8 bit device address word following a start condition to enable the chip for a read or write operation (refer to Figure 4). The device address word consists of a mandatory one, zero sequence for the first four most significant bits as shown. This is common to all the E2PROM devices. The next three bits are don't care for the AT24C21. The eighth bit of the device address is the read/write operation select bit. A read operation is initiated if this bit is high and a write operation is initiated if this bit is low. Upon a compare of the device address, the E2PROM will output a zero. If a compare is not made, the chip will return to a standby state. STANDBY MODE: The AT24C21 features a low power standby mode which is enabled: (a) upon power-up and (b) after the receipt of the STOP bit and the completion of any internal operations.
Bi-Directional Mode Operation:
CLOCK and DATA TRANSITIONS: The SDA pin is normally pulled high with an external device. Data on the SDA pin may change only during SCL low time periods (refer to Data Validity timing diagram). Data changes during SCL high periods will indicate a start or stop condition as defined below. START CONDITION: A high-to-low transition of SDA with SCL high is a start condition which must precede any other command (refer to Start and Stop Definition timing diagram). STOP CONDITION: A low-to-high transition of SDA with SCL high is a stop condition. After a read or write sequence, the stop command will place the E2PROM in a standby power mode (refer to Start and Stop Definition timing diagram).
Figure 3. Mode Transition
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AT24C21
AT24C21
Bus Timing SCL: Serial Clock SDA: Serial Data I/O
Write Cycle Timing SCL: Serial Clock SDA: Serial Data I/O
Note:
The write cycle time tWR is the time from a valid stop condition of a write sequence to the end of the internal clear/write cycle.
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Data Validity
Start and Stop Definition
Output Acknowledge
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AT24C21
AT24C21
Write Operations
BYTE WRITE: A write operation requires an 8 bit data word addresses following the device address word and acknowlegement. Upon receipt of this address, the E2PROM will again respond with a zero and then clock in the first 8 bit data word. Following receipt of the 8 bit data word, the E2PROM will output a zero and the addressing device, such as a microcontroller, must terminate the write sequence with a stop condition. At this time the E2PROM enters an internally-timed write cycle to the nonvolatile memory. All inputs are disabled during this write cycle and the E2PROM will not respond until the write is complete (refer to Figure 5). It is required that VCLK be held at a high logic level in order to program the device. This applies to byte write and page write operation. Note that VCLK can go low while the device is in its self-timed program operation and not affect programming. PAGE WRITE: The AT24C21 is capable of an 8-byte page write. A page write is initiated the same as a byte write, but the microcontroller does not send a stop condition after the first data word is clocked in. Instead, after the E2PROM acknowledges receipt of the first data word, the microcontroller can transmit up to seven more data words. The E2PROM will respond with a zero after each data word received. The microcontroller must terminate the page write sequence with a stop condition (refer to Figure 6). The data word address lower three bits are internally incremented following the receipt of each data word. The higher data word address bits are not incremented, retaining the memory page row location. If more than eight data words are transmitted to the E2PROM, the data word address will "roll over" and previous data will be overwritten. The address "roll over" during write is from the last byte of the current page to the first byte of the same page. It is required that VCLK be held at a high logic level in order to program the device. This applies to byte write and page write operation. Note that VCLK can go low while the device is in its self-timed program operation and not affect programming. ACKNOWLEDGE POLLING: Once the internally-timed write cycle has started and the E2PROM inputs are disabled, acknowledge polling can be initiated. This involves sending a start condition followed by the device address word. The read/write bit is representative of the operation desired. Only if the internal write cycle has completed will the E2PROM respond with a zero allowing the read or write sequence to continue. WRITE PROTECTION: When VCLK pin is connected to GND and in the Bi-Directional Mode, the entire memory is protected and becomes ROM only. This protects the device memory from any inadvertent write operations. NOISE PROTECTION: Special internal circuitry placed on the SDA and SCL pins prevent small noise spikes from activating the device. Furthermore, the AT24C21 employs a low VCC detector circuit which disables the erase\write logic whenever VCC falls below 1.5 volts.
Read Operations
Read operations are initiated the same way as write operations with the exception that the read/write select bit in the device address word is set to one. There are three read operations: current address read, random address read and sequential read. CURRENT ADDRESS READ: The internal data word address counter maintains the last address accessed during the last read or write operation, incremented by one. This address stays valid between operations as long as the chip power is maintained. The address "roll over" during read is from the last byte of the last memory page to the first byte of the first page. Once the device address with the read/write select bit set to one is clocked in and acknowledged by the E2PROM, the current address data word is serially clocked out. The microcontroller does not respond with an input zero but does generate a following stop condition (refer to Figure 7). RANDOM READ: A random read requires a "dummy" byte write sequence to load in the data word address. Once the device address word and data word address are clocked in and acknowledged by the E2PROM, the microcontroller must generate another start condition. The microcontroller now initiates a current address read by sending a device address with the read/write select bit high. The E2PROM acknowledges the device address and serially clocks out the data word. The microcontroller does not respond with a zero but does generate a following stop condition (refer to Figure 8). SEQUENTIAL READ: Sequential reads are initiated by either a current address read or a random address read. After the microcontroller receives a data word, it responds with an acknowledge. As long as the E2PROM receives an acknowledge, it will continue to increment the data word address and serially clock out sequential data words. When the memory address limit is reached, the data word address will "roll over" and the sequential read will continue. The sequential read operation is terminated when the microcontroller does not respond with a zero but does generate a following stop condition (refer to Figure 9). 2-21
Figure 4. Device Address
Figure 5. Byte Write
Figure 6. Page Write
(* = Don't care bits)
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AT24C21
AT24C21
Figure 7. Current Address Read
Figure 8. Random Read
Figure 9. Sequential Read
(* = Don't care bits)
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Ordering Information
tWR (max) (ms) 10 ICC (max) (A) 3000 3000 ISB (max) (A) 4 4 fMAX (kHz) 400 400 Ordering Code AT24C21-10PC-2.5 AT24C21-10SC-2.5 AT24C21-10PI-2.5 AT24C21-10SI-2.5 Package 8P3 8S1 8P3 8S1 Operation Range Commercial (0C to 70C) Industrial (-40C to 85C)
Package Type 8P3 8S1 8 Lead, 0.300" Wide, Plastic Dual Inline Package (PDIP) 8 Lead, 0.150" Wide, Plastic Gull Wing Small Outline (JEDEC SOIC) Options -2.5 Low Voltage (2.5V to 5.5V)
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AT24C21

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