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1 features ? low-voltage and standard-voltage operation ? 1.8 (v cc = 1.8v to 3.6v) internally organized as 32,768 x 8 two-wire serial interface schmitt trigger, filtered inputs for noise suppression bidirectional data transfer protocol 1 mhz (3.6v, 2.7v, 2.5v), and 400 khz (1.8v) compatibility write protect pin for hardware and software data protection 64-byte page write mode (partial page writes allowed) self-timed write cycle (5 ms max) high reliability ? endurance: one million write cycles ? data retention: 40 years extended temperature and lead-free/halogen-free devices available 8-lead jedec pdip, 8-lead jedec soic, 8-lead map, 8-lead tssop, and 8-ball dbga2 tm packages description the AT24C256B provides 262,144 bits of serial electrically erasable and programma- ble read-only memory (eeprom) organized as 32,768 words of 8 bits each. the device?s cascadable feature allows up to eight devices to share a common two-wire bus. the device is optimized for use in many industrial and commercial applications where low-power and low-voltage operation are essential. the devices are available in space-saving 8-lead jedec pdip, 8-lead jedec soic, 8-lead map, 8-lead tssop, and 8-ball dbga2 packages. in addition, the entire family is available in a 1.8v (1.8v to 3.6v) version. two-wire serial eeprom 256k (32,768 x 8) AT24C256B preliminary rev. 5080a?seepr?9/04 table 1. pin configurations pin name function a0?a2 address inputs sda serial data scl serial clock input wp write protect nc no connect gnd ground a0 a1 a2 gnd vcc wp s cl s da 1 2 3 4 8 7 6 5 vcc wp s cl s da 8 7 6 5 1 2 3 4 a0 a1 a2 gnd 8 7 6 5 1 2 3 4 vcc wp s cl s da a0 a1 a2 gnd 8 7 6 5 1 2 3 4 vcc wp s cl s da a0 a1 a2 gnd 8 -le a d pdip 8 -le a d s oic 8 -le a d dbga2 8 -le a d map a0 a1 a2 gnd vcc wp s cl s da 1 2 3 4 8 7 6 5 8 -le a d t ss op bottom view bottom view
2 AT24C256B 5080a?seepr?9/04 figure 1. block diagram absolute maximum ratings* operating temperature ......................................? 55 c to +125 c *notice: stresses beyond those listed under ?absolute maximum ratings? may cause permanent dam- age to the device. this is a stress rating only; 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. storage temperature .........................................? 65 c to +150 c voltage on any pin with respect to ground ........................................ ? 1.0v to +5.0v maximum operating voltage ............................................ 4.3v dc output current........................................................ 5.0 ma
3 AT24C256B 5080a?seepr?9/04 pin description serial clock (scl): the scl input is used to positive-edge clock data into each eeprom 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. device/page addresses (a2, a1, a0): the a2, a1, and a0 pins are device address inputs that are hardwired (directly to gnd or to vcc) for compatibility with other at24cxx devices. when the pins are hardwired, as many as eight 256k devices may be addressed on a single bus system. (device addressing is discussed in detail under ?device addressing,? page 8.) a device is selected when a corresponding hardware and software match is true. if these pins are left floating, the a2, a1, and a0 pins will be internally pulled down to gnd. how- ever, due to capacitive coupling that may appear during customer applications, atmel recommends always connecting the address pins to a known state. when using a pull-up resistor, atmel recommends using 10k ? or less. write protect (wp): the write protect input, when connected to gnd, allows normal write operations. when wp is connected directly to vcc, all write operations to the memory are inhibited. if the pin is left floating, the wp pin will be internally pulled down to gnd. however, due to capacitive coupling that may appear during customer applications, atmel recommends always connecting the wp pins to a known state. when using a pull-up resistor, atmel recom- mends using 10k ? or less. memory organization AT24C256B, 256k serial eeprom: the 256k is internally organized as 512 pages of 64 bytes each. random word addressing requires a 15-bit data word address.
4 AT24C256B 5080a?seepr?9/04 table 1 . pin capacitance (1) note: 1. this parameter is characterized and is not 100% tested. table 2 . dc characteristics notes: 1. v il min and v ih max are reference only and are not tested. applicable over recommended operating range from t a = 25 c, f = 1.0 mhz, v cc = +1.8v symbol test condition max units conditions c i/o input/output capacitance (sda) 8 pf v i/o = 0v c in input capacitance (a 0 , a 1 , scl) 6 pf v in = 0v applicable over recommended operating range from: t ai = ? 40 c to +85 c, v cc = +1.8v to +3.6v (unless otherwise noted) symbol parameter test condition min typ max units v cc1 supply voltage 1.8 3.6 v i cc1 supply current v cc = 3.6v read at 400 khz 1.0 2.0 ma i cc2 supply current v cc = 3.6v write at 400 khz 2.0 3.0 ma i sb1 standby current (1.8v option) v cc = 1.8v v in = v cc or v ss 1.0 a v cc = 3.6v 3.0 i li input leakage current v in = v cc or v ss 0.10 3.0 a i lo output leakage current v out = v cc or v ss 0.05 3.0 a v il input low level (1) ? 0.6 v cc x 0.3 v v ih input high level (1) v cc x 0.7 v cc + 0.5 v v ol2 output low level v cc = 3.0v i ol = 2.1 ma 0.4 v v ol1 output low level v cc = 1.8v i ol = 0.15 ma 0.2 v
5 AT24C256B 5080a?seepr?9/04 table 3 . ac characteristics (industrial temperature) notes: 1. this parameter is characterized and is not 100% tested. 2. ac measurement conditions: r l (connects to v cc ): 1.3 k ? (2.5v, 3.6v), 10 k ? (1.8v) input pulse voltages: 0.3 v cc to 0.7 v cc input rise and fall times: 50 ns input and output timing reference voltages: 0.5 v cc applicable over recommended operating range from t ai = ? 40 c to +85 c, v cc = +1.8v to +3.6v, cl = 100 pf (unless oth- erwise noted). test conditions are listed in note 2. symbol parameter 1.8-volt 2.5-volt 3.6-volt units min max min max min max f scl clock frequency, scl 400 1000 1000 khz t low clock pulse width low 1.3 0.4 0.4 s t high clock pulse width high 0.6 0.4 0.4 s t aa clock low to data out valid 0.05 0.9 0.05 0.55 0.05 0.55 s t buf time the bus must be free before a new transmission can start (1) 1.3 0.5 0.5 s t hd.sta start hold time 0.6 0.25 0.25 s t su.sta start set-up time 0.6 0.25 0.25 s t hd.dat data in hold time 0 0 0 s t su.dat data in set-up time 100 100 100 ns t r inputs rise time (1) 0.3 0.3 0.3 s t f inputs fall time (1) 300 100 100 ns t su.sto stop set-up time 0.6 0.25 0.25 s t dh data out hold time 50 50 50 ns t wr write cycle time 5 5 5 ms endurance (1) 25c, page mode, 3.3v 1,000,000 write cycles
6 AT24C256B 5080a?seepr?9/04 device 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 (see figure 2). data changes during scl high periods will indicate a start or stop condition as defined below. figure 2. data validity start condition: a high-to-low transition of sda with scl high is a start condition that must precede any other command (see figure 3). figure 3. start and stop definition stop condition: a low-to-high transition of sda with scl high is a stop condition. after a read sequence, the stop command will place the eeprom in a standby power mode (see fig- ure 3). acknowledge: all addresses and data words are serially transmitted to and from the eeprom in 8-bit words. the eeprom sends a ?0? during the ninth clock cycle to acknowl- edge that it has received each word. standby mode: the AT24C256B features a low-power standby mode that is enabled upon power-up and after the receipt of the stop bit and the completion of any internal operations. s da s cl s ta rt s top
7 AT24C256B 5080a?seepr?9/04 memory reset: after an interruption in protocol, power loss or system reset, any two-wire part can be reset by following these steps: 1. clock up to 9 cycles; 2. look for sda high in each cycle while scl is high; 3. create a start condition as sda is high. figure 4. bus timing figure 5. write cycle timing note: 1. the write cycle time t wr is the time from a valid stop condition of a write sequence to the end of the internal clear/write cycle. t wr (1) stop condition start condition wordn ack 8th bit scl sda
8 AT24C256B 5080a?seepr?9/04 figure 6. output acknowledge device addressing the 256k eeprom requires an 8-bit device address word following a start condition to enable the chip for a read or write operation (see figure 7). the device address word consists of a mandatory ?1?, ?0? sequence for the first four most significant bits as shown. this is common to all two-wire eeprom devices. figure 7. device address the next three bits are the a2, a1, a0 device address bits to allow as many as eight devices on the same bus. these bits must compare to their corresponding hardwired input pins. the a2, a1, and a0 pins use an internal proprietary circuit that biases them to a logic low condition if the pins are allowed to float. 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 eeprom will output a ?0?. if a compare is not made, the device will retu rn to a standby state. data security: the AT24C256B has a hardware data protection scheme that allows the user to write protect the whole memory when the wp pin is at v cc . m s b 1 0 1 0 a2 a1 a0 r/w l s b
9 AT24C256B 5080a?seepr?9/04 write operations byte write: a write operation requires two 8-bit data word addresses following the device address word and acknowledgment. upon receip t of this address, the eeprom will again respond with a ?0? and then clock in the first 8-bit data word. following receipt of the 8-bit data word, the eeprom will output a ?0?. the addressing device, such as a microcontroller, must then terminate the write sequence with a stop condition. at this time the eeprom enters an internally-timed write cycle, t wr , to the nonvolatile memory. all inputs are disabled during this write cycle and the eeprom will not res pond until the write is complete (see figure 8). figure 8. byte write note: * = don?t care bit page write: the 256k eeprom is capable of 64-byte page writes. a page write is initiated the same way as a byte write, but the microcontroller does not send a stop condition after the first data word is clocked in. instead, after the eeprom acknowledges receipt of the first data word, the microcontroller can transmit up to 63 more data words. the eeprom will respond with a ?0? after each data word received. the microcontroller must ter- minate the page write sequence with a stop condition (see figure 9). figure 9. page write note: * = don?t care bit the data word address lower six 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. when the word address, internally generated, reaches the page boundary, the following byte is placed at the beginning of the same page. if more than 64 data words are transmitted to the eeprom, 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. acknowledge polling: once the internally-timed write cycle has started and the eeprom 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 eeprom respond with a ?0?, allowing the read or write sequence to continue.
10 AT24C256B 5080a?seepr?9/04 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 ?1?. 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 ?1? is clocked in and acknowl- edged by the eeprom, the current address data word is serially clocked out. the microcontroller does not respond with an input ?0? but does generate a following stop condition (see figure 10). figure 10. current address read 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 eeprom, 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 eeprom acknowledges the device address and serially clocks out the data word. the microcontroller does not respond with a ?0? but does generate a follow- ing stop condition (see figure 11). figure 11. random read note: * = don?t care bit
11 AT24C256B 5080a?seepr?9/04 sequential read: sequential reads are initiated by either a current address read or a ran- dom address read. after the microcontroller receives a data word, it responds with an acknowledge. as long as the eeprom 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 addre ss will ?roll over? and the sequential read will con- tinue. the sequential read operation is terminated when the microcontroller does not respond with a ?0? but does generate a following stop condition (see figure 12). figure 12. sequential read
12 AT24C256B 5080a?seepr?9/04 AT24C256B ordering information ordering code package operation range AT24C256B-10pu-1.8 AT24C256Bn-10su-1.8 AT24C256Bu2-10uu-1.8 AT24C256B-10tu-1.8 AT24C256By1-10yu-1.8 8p3 8s1 8u2-1 8a2 8y1 lead-free/halogen-free industrial temperature (? 40 c to 85 c package type 8p3 8-lead, 0.300" wide, plastic dual inline package (pdip) 8s1 8-lead, 0.150" wide, plastic gull wing small outline package (jedec soic) 8u2-1 8-ball, die ball grid array package (dbga2) 8a2 8-lead, 0.170" wide, thin shrink small outline package (tssop) 8y1 8-lead, 4.90 mm x 3.00 mm body, dual footprint, non-leaded, miniature array package (map) options ? 1.8 low-voltage (1.8v to 3.6v)
13 AT24C256B 5080a?seepr?9/04 packaging information 8p3 ? pdip 2 3 25 orch a rd p a rkw a y sa n jo s e, ca 951 3 1 title drawing no. r rev. 8 p 3 , 8 -le a d, 0. 3 00" wide body, pl as tic d ua l in-line p a ck a ge (pdip) 01/09/02 8 p 3 b note s : 1. thi s dr a wing i s for gener a l inform a tion only; refer to jedec dr a wing m s -001, v a ri a tion ba, for a ddition a l inform a tion. 2. dimen s ion s a a nd l a re me asu red with the p a ck a ge s e a ted in jedec s e a ting pl a ne g au ge g s - 3 . 3 . d, d1 a nd e1 dimen s ion s do not incl u de mold fl as h or protr us ion s . mold fl as h or protr us ion s s h a ll not exceed 0.010 inch. 4. e a nd ea me asu red with the le a d s con s tr a ined to b e perpendic u l a r to d a t u m. 5. pointed or ro u nded le a d tip s a re preferred to e as e in s ertion. 6. b 2 a nd b3 m a xim u m dimen s ion s do not incl u de d a m ba r protr us ion s . d a m ba r protr us ion s s h a ll not exceed 0.010 (0.25 mm). common dimen s ion s (unit of me asu re = inche s ) s ymbol min nom max note d d1 e e1 e l b 2 b a2 a 1 n ea c b3 4 plc s a ? ? 0.210 2 a2 0.115 0.1 3 0 0.195 b 0.014 0.01 8 0.022 5 b 2 0.045 0.060 0.070 6 b3 0.0 3 0 0.0 3 9 0.045 6 c 0.00 8 0.010 0.014 d 0. 3 55 0. 3 65 0.400 3 d1 0.005 ? ? 3 e 0. 3 00 0. 3 10 0. 3 25 4 e1 0.240 0.250 0.2 8 0 3 e 0.100 b s c ea 0. 3 00 b s c 4 l 0.115 0.1 3 0 0.150 2 top view s ide view end view
14 AT24C256B 5080a?seepr?9/04 8s1 ? jedec soic 1150 e. cheyenne mtn. blvd. colorado springs, co 80906 title drawing no. r rev. note: 10/7/03 8s1 , 8-lead (0.150" wide body), plastic gull wing small outline (jedec soic) 8s1 b common dimensions (unit of measure = mm) symbol min nom max note a1 0.10 ? 0.25 these drawings are for general information only. refer to jedec drawing ms-012, variation aa for proper dimensions, tolerances, datums, etc. a 1.35 ? 1.75 b 0.31 ? 0.51 c 0.17 ? 0.25 d 4.80 ? 5.00 e1 3.81 ? 3.99 e 5.79 ? 6.20 e 1.27 bsc l 0.40 ? 1.27 ? 0? ? 8? ? top view end view side view e b d a a1 n e 1 c e1 l
15 AT24C256B 5080a?seepr?9/04 8u2-1 ? dbga2 1150 e. cheyenne mtn. blvd. color a do s pring s , co 8 0906 title drawing no. r rev. po 8 u2-1 a 6/24/0 3 common dimen s ion s (unit of me asu re = mm) s ymbol min nom max note 8 u2-1, 8 - ba ll, 2. 3 5 x 3 .7 3 mm body, 0.75 mm pitch, s m a ll die b a ll grid arr a y p a ck a ge (dbga2) a 0. 8 1 0.91 1.00 a1 0.15 0.20 0.25 a2 0.40 0.45 0.50 b 0.25 0. 3 0 0. 3 5 1 d 2. 3 5 b s c e 3 .7 3 b s c e 0.75 b s c e1 0.74 ref d 0.75 b s c d1 0. 8 0 ref 1. dimen s ion ' b ' i s me asu red a t the m a xim u m s older ba ll di a meter. thi s dr a wing i s for gener a l inform a tion only. d a s ide view top view bottom view 8 s older b a ll s 1 a b c d 2 (e1) e a1 ball pad corner (d1) 1. b a1 a2 d a1 ball pad corner e
16 AT24C256B 5080a?seepr?9/04 8a2 ? tssop 2325 orchard parkway san jose, ca 95131 title drawing no. r rev. 5/30/02 common dimensions (unit of measure = mm) symbol min nom max note d 2.90 3.00 3.10 2, 5 e 6.40 bsc e1 4.30 4.40 4.50 3, 5 a ? ? 1.20 a2 0.80 1.00 1.05 b 0.19 ? 0.30 4 e 0.65 bsc l 0.45 0.60 0.75 l1 1.00 ref 8a2 , 8-lead, 4.4 mm body, plastic thin shrink small outline package (tssop) notes: 1. this drawing is for general information only. refer to jedec drawing mo-153, variation aa, for proper dimensions, tolerances, datums, etc. 2. dimension d does not include mold flash, protrusions or gate burrs. mold flash, protrusions and gate burrs shall not exceed 0.15 mm (0.006 in) per side. 3. dimension e1 does not include inter-lead flash or protrusions. inter-lead flash and protrusions shall not exceed 0.25 mm (0.010 in) per side. 4. dimension b does not include dambar protrusion. allowable dambar protrusion shall be 0.08 mm total in excess of the b dimension at maximum material condition. dambar cannot be located on the lower radius of the foot. minimum space between protrusion and adjacent lead is 0.07 mm. 5. dimension d and e1 to be determined at datum plane h. 8a2 b side view end view top view a2 a l l1 d 1 2 3 e1 n b pin 1 indicator this corner e e
17 AT24C256B 5080a?seepr?9/04 8y1 ? map a ? ? 0.90 a1 0.00 ? 0.05 d 4.70 4.90 5.10 e 2. 8 0 3 .00 3 .20 d1 0. 8 5 1.00 1.15 e1 0. 8 5 1.00 1.15 b 0.25 0. 3 0 0. 3 5 e 0.65 typ l 0.50 0.60 0.70 pin 1 index area d e a a1 b 8 7 6 e 5 l d1 e1 pin 1 index area 1 2 3 4 a to p v i e w end view bottom view s ide view 2 3 25 orch a rd p a rkw a y sa n jo s e, ca 951 3 1 title drawing no. r rev. 8 y1, 8 -le a d (4.90 x 3 .00 mm body) m s op arr a y p a ck a ge (map) y1 c 8 y1 2/2 8 /0 3 common dimen s ion s (unit of me asu re = mm) s ymbol min nom max note
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