Preliminary FM24CL64 64Kb 2.7V-3.6V FRAM Serial Memory Features 64K bit Ferroelectric Nonvolatile RAM • Organized as 8,192 x 8 bits • Unlimited read/write cycles • 10 year data retention at 85° C • NoDelay™ write • Advanced high-reliability ferroelectric process Fast Two-wire Serial Interface • Up to 1 MHz maximum bus frequency • Direct hardware replacement for EEPROM • Supports legacy timing for 100 kHz & 400 kHz Description Low Power Operation • True 2.7V-3.6V operation • 75 µA Active current (100 kHz) • 1 µA Standby current Industry Standard Configuration • Industrial temperature -40° C to +85° C • 8-pin SOP Pin Configuration The FM24CL64 is a 64-kilobit nonvolatile memory employing an advanced ferroelectric process. A ferroelectric random access memory or FRAM is nonvolatile but operates in other respects as a RAM. It provides reliable data retention for 10 years while eliminating the complexities, overhead, and system level reliability problems caused by EEPROM and other nonvolatile memories. The FM24CL64 performs write operations at bus speed. No write delays are incurred. Data is written to the memory array mere hundreds of nanoseconds after it has been successfully transferred to the device. The next bus cycle may commence immediately. Fast-write time and unlimited read/write endurance make it superior to other types of nonvolatile memory and a good substitute for ordinary SRAM These capabilities make the FM24CL64 ideal for nonvolatile memory applications requiring frequent or rapid writes. Examples range from data collection where the number of write cycles may be critical, to demanding industrial controls where the long write time of EEPROM can cause data loss. The combination of features allows more frequent data writing with less overhead for the system. A0 A1 A2 VSS VDD WP SCL SDA Pin Names A0-A2 SDA SCL WP VSS VDD Function Device Select Address Serial Data/address Serial Clock Write Protect Ground Supply Voltage Ordering Information FM24CL64-S 8-pin SOP The FM24CL64 provides substantial benefits to users of serial EEPROM, yet these benefits are available in a hardware drop-in replacement. The FM24CL64 is provided in industry standard 8-pin surface mount package using a familiar two-wire protocol. It is guaranteed over an industrial temperature range of -40°C to +85°C. This data sheet contains specifications for a product under development. Characterization is not complete; the specifications may change without notice. Ramtron International Corporation 1850 Ramtron Drive, Colorado Springs, CO 80921 (800) 545-FRAM, (719) 481-7000, Fax (719) 481-7058 www.ramtron.com 9 May 2001 1/1 Ramtron FM24CL64 Figure 1. FM24CL64 Block Diagram Address Latch Counter 2,048 x 32 FRAM Array 8 ` SDA Serial to Parallel Converter Data Latch SCL WP Control Logic A0-A2 Pin Description Pin Name A0-A2 Pin Number 1-3 I/O I VSS SDA 4 5 I I/O SCL 6 I WP 7 I VDD 8 I 9 May 2001 Pin Description Address 0-2. These pins are used to select one of up to 8 devices of the same type on the same two-wire bus. To select the device, the address value on the three pins must match the corresponding bits contained in the device address. The address pins are pulled down internally. Ground Serial Data Address. This is a bi-directional line for the two-wire interface. It is open-drain and is intended to be wire-ORed with other devices on the two-wire bus. The input buffer incorporates a schmitt trigger for noise immunity and the output driver includes slope control for falling edges. A pull-up resistor is required. Serial Clock. The serial clock line for the two-wire interface. Data is clocked out of the part on the falling edge, and in on the rising edge. The SCL input also incorporates a schmit trigger input for noise immunity. Write Protect. When tied to VDD, addresses in the entire memory map will be write-protected. When WP is connected to ground, all addresses may be written. This pin is pulled down internally. Supply Voltage 2.7V to 3.6V. 2/2 Ramtron FM24CL64 Overview Two-wire Interface The FM24CL64 is a serial FRAM memory. The memory array is logically organized as a 8,192 x 8 bit memory array and is accessed using an industry standard two-wire interface. Functional operation of the FRAM is similar to serial EEPROMs. The major difference between the FM24CL64 and a serial EEPROM with the same pin-out relates to its superior write performance. The FM24CL64 employs a bi-directional two-wire bus protocol using few pins or board space. Figure 2 illustrates a typical system configuration using the FM24CL64 in a microcontroller-based system. The industry standard two-wire bus is familiar to many users but is described in this section. Memory Architecture When accessing the FM24CL64, the user addresses 8,192 locations each with 8 data bits. These data bits are shifted serially. The 8,192 addresses are accessed using the two-wire protocol, which includes a slave address (to distinguish other non-memory devices), and an extended 16-bit address. Only the lower 13 bits are used by the decoder for accessing the memory. The upper three address bits should be set to 0 for compatibility with larger devices in the future. The access time for memory operation is essentially zero beyond the time needed for the serial protocol. That is, the memory is read or written at the speed of the two-wire bus. Unlike an EEPROM, it is not necessary to poll the device for a ready condition since writes occur at bus speed. That is, by the time a new bus transaction can be shifted into the part, a write operation will be complete. This is explained in more detail in the interface section below. Users expect several obvious system benefits from the FM24CL64 due to its fast write cycle and high endurance as compared with EEPROM. However there are less obvious benefits as well. For example in a high noise environment, the fast-write operation is less susceptible to corruption than an EEPROM since it is completed quickly. By contrast, an EEPROM requiring milliseconds to write is vulnerable to noise during much of the cycle. By convention, any device that is sending data onto the bus is the transmitter while the target device for this data is the receiver. The device that is controlling the bus is the master. The master is responsible for generating the clock signal for all operations. Any device on the bus that is being controlled is a slave. The FM24CL64 always is a slave device. The bus protocol is controlled by transition states in the SDA and SCL signals. There are four conditions including start, stop, data bit, or acknowledge. Figure 3 illustrates the signal conditions that specify the four states. Detailed timing diagrams are in the electrical specifications. Figure 2. Typical System Configuration VDD Rmin = 1.1 KΩ Rmax = tR/Cbus Microcontroller SDA SCL SDA SCL FM24CL64 FM24CL64 A0 A1 A2 A0 A1 A2 Note that it is the user’s responsibility to ensure that VDD is within data sheet tolerances to prevent incorrect operation. 9 May 2001 3/3 Ramtron FM24CL64 Figure 3. Data Transfer Protocol SCL SDA 7 Stop (Master) Start (Master) 6 Data bits (Transmitter) Start Condition A start condition is indicated when the bus master drives SDA from high to low while the SCL signal is high. All commands should be preceded by a start condition. An operation in progress can be aborted by asserting a start condition at any time. Aborting an operation using the start condition will ready the FM24CL64 for a new operation. If during operation the power supply drops below the specified VDD minimum, the system should issue a start condition prior to performing another operation. Stop Condition A stop condition is indicated when the bus master drives SDA from low to high while the SCL signal is high. All operations using the FM24CL64 should end with a stop condition. If an operation is in progress when a stop is asserted, the operation will be aborted. The master must have control of SDA (not a memory read) in order to assert a stop condition. Data/Address Transfer All data transfers (including addresses) take place while the SCL signal is high. Except under the two conditions described above, the SDA signal should not change while SCL is high. Acknowledge The acknowledge takes place after the 8th data bit has been transferred in any transaction. During this state the transmitter should release the SDA bus to allow the receiver to drive it. The receiver drives the SDA signal low to acknowledge receipt of the byte. If the receiver does not drive SDA low, the condition is a no-acknowledge and the operation is aborted. 0 Data bit Acknowledge (Transmitter) (Receiver) Second and most common, the receiver does not acknowledge to deliberately end an operation. For example, during a read operation, the FM24CL64 will continue to place data onto the bus as long as the receiver sends acknowledges (and clocks). When a read operation is complete and no more data is needed, the receiver must not acknowledge the last byte. If the receiver acknowledges the last byte, this will cause the FM24CL64 to attempt to drive the bus on the next clock while the master is sending a new command such as stop. Slave Address The first byte that the FM24CL64 expects after a start condition is the slave address. As shown in Figure 4, the slave address contains the device type, the device select address bits, and a bit that specifies if the transaction is a read or a write. Bits 7-4 are the device type and should be set to 1010b for the FM24CL64. These bits allow other types of function types to reside on the 2-wire bus within an identical address range. Bits 3-1 are the address select bits. They must match the corresponding value on the external address pins to select the device. Up to eight, FM24CL64s can reside on the same two-wire bus by assigning a different address to each. Bit 0 is the read/write bit. A 0 indicates a write operation. The receiver would fail to acknowledge for two distinct reasons. First is that a byte transfer fails. In this case, the no-acknowledge ceases the current operation so that the part can be addressed again. This allows the last byte to be recovered in the event of a communication error. 9 May 2001 4/4 Ramtron FM24CL64 Memory Operation Figure 4. Slave Address Device Select Slave ID 1 0 1 0 A2 A1 A0 R/W 7 6 5 4 3 2 1 0 Addressing Overview After the FM24CL64 (as receiver) acknowledges the device address, the master can place the memory address on the bus for a write operation. The address requires two bytes. The first is the MSB. Since the device uses only 13 address bits, the value of the upper three bits are don’t care. Following the MSB is the LSB with the remaining eight address bits. The address value is latched internally. Each access causes the latched address value to be incremented automatically. The current address is the value that is held in the latch -- either a newly written value or the address following the last access. The current address will be held for as long as power remains or until a new value is written. Reads always use the current address. A random read address can be loaded by beginning a write operation as explained below. After transmission of each data byte, just prior to the acknowledge, the FM24CL64 increments the internal address latch. This allows the next sequential byte to be accessed with no additional addressing. After the last address (1FFFh) is reached, the address latch will roll over to 0000h. There is no limit to the number of bytes that can be accessed with a single read or write operation. Data Transfer After the address information has been transmitted, data transfer between the bus master and the FM24CL64 can begin. For a read operation the FM24CL64 will place 8 data bits on the bus then wait for an acknowledge from the master. If the acknowledge occurs, the FM24CL64 will transfer the next sequential byte. If the acknowledge is not sent, the FM24CL64 will end the read operation. For a write operation, the FM24CL64 will accept 8 data bits from the master then send an acknowledge. All data transfer occurs msb (most significant bit) first. The FM24CL64 is designed to operate in a manner very similar to other 2-wire interface memory products. The major differences result from the higher performance write capability of FRAM technology. These improvements result in some differences between the FM24CL64 and a similar configuration EEPROM during writes. The complete operation for both writes and reads is explained below. Write Operation All writes begin with a device address, then a memory address. The bus master indicates a write operation by setting the lsb of the device address to a 0. After addressing, the bus master sends each byte of data to the memory and the memory generates an acknowledge condition. Any number of sequential bytes may be written. If the end of the address range is reached internally, the address counter will wrap from 1FFFh to 0000h. Unlike other nonvolatile memory technologies, there is no effective write delay with FRAM. Since the read and write access times of the underlying memory are the same, the user experiences no delay through the bus. The entire memory cycle occurs in less time than a single bus clock. Therefore, any operation including read or write can occur immediately following a write. Acknowledge polling, a technique used with EEPROMs to determine if a write is complete is unnecessary and will always return a ready condition. Internally, an actual memory write occurs after the 8th data bit is transferred. It will be complete before the acknowledge is sent. Therefore, if the user desires to abort a write without altering the memory contents, this should be done using start or stop condition prior to the 8th data bit. The FM24CL64 uses no page buffering. The memory array can be write protected using the WP pin. Setting the WP pin to a high condition (VDD) will write-protect all addresses. The FM24CL64 will not acknowledge data bytes that are written to protected addresses. In addition, the address counter will not increment if writes are attempted to these addresses. Setting WP to a low state (VSS) will deactivate this feature. WP is pulled down internally. Figure 5 below illustrates both a single-byte and multiple-write. 9 May 2001 5/5 Ramtron FM24CL64 Figure 5 Byte Write Start By Master S Stop Address & Data Slave Address 0 A Address MSB A Address LSB A Data Byte A P By FM24CL64 Acknowledge Figure 6 Multiple Byte Write Start Stop Address & Data By Master S By FM24CL64 Slave Address 0 A Address MSB A Address LSB Data Byte A Data Byte A P Acknowledge Read Operation There are two basic types of read operations. They are current address read and selective address read. In a current address read, the FM24CL64 uses the internal address latch to supply the address. In a selective read, the user performs a procedure to set the address to a specific value. most likely create a bus contention as the FM24CL64 attempts to read out additional data onto the bus. The four valid methods are as follows. 1. 2. Current Address & Sequential Read As mentioned above the FM24CL64 uses an internal latch to supply the address for a read operation. A current address read uses the existing value in the address latch as a starting place for the read operation. The system reads from the address immediately following that of the last operation. To perform a current address read, the bus master supplies a device address with the lsb set to 1. This indicates that a read operation is requested. After receiving the complete device address, the FM24CL64 will begin shifting out data from the current address on the next clock. The current address is the value held in the internal address latch. Beginning with the current address, the bus master can read any number of bytes. Thus, a sequential read is simply a current address read with multiple byte transfers. After each byte the internal address counter will be incremented. Each time the bus master acknowledges a byte, this indicates that the FM24CL64 should read out the next sequential byte. There are four ways to properly terminate a read operation. Failing to properly terminate the read will 9 May 2001 A 3. 4. The bus master issues a no-acknowledge in the 9th clock cycle and a stop in the 10th clock cycle. This is illustrated in the diagrams below. This is preferred. The bus master issues a no-acknowledge in the 9th clock cycle and a start in the 10th. The bus master issues a stop in the 9th clock cycle. The bus master issues a start in the 9th clock cycle. If the internal address reaches 1FFFh, it will wrap around to 0000h on the next read cycle. Figures 7 and 8 below show the proper operation for current address reads. Selective (Random) Read There is a simple technique that allows a user to select a random address location as the starting point for a read operation. This involves using the first three bytes of a write operation to set the internal address followed by subsequent read operations. To perform a selective read, the bus master sends out the device address with the lsb set to 0. This specifies a write operation. According to the write protocol, the bus master then sends the address bytes that are loaded into the internal address latch. After the FM24CL64 acknowledges the address, the bus master issues a start condition. This simultaneously aborts the write operation and allows the read command to be issued with the device address lsb set to a 1. The operation is now a current address read. 6/6 Ramtron FM24CL64 Figure 7 Current Address Read Start By Master No Acknowledge Address Stop S Slave Address 1 A By FM24CL64 Data Byte Acknowledge 1 P Data Figure 8 Sequential Read Start By Master Address No Acknowledge Acknowledge Stop S Slave Address By FM24CL64 1 A Data Byte A Acknowledge Data Byte 1 P Data Figure 9 Selective (Random) Read Start Address By Master Start No Acknowledge Address Stop S Slave Address By FM24CL64 0 A Address MSB A Address LSB Acknowledge Applications Clearly the strength of higher write endurance and faster writes make FRAM superior to EEPROM in all but one-time programmable applications. The advantage is most obvious in data collection environments where writes are frequent and data must be nonvolatile, but the benefits combine in other ways. A short list of ideas is provided here. 1. Data collection. In applications where data is collected and saved, FRAM provides a superior alternative to other solutions. It is more cost effective than battery backup for SRAM and provides better write attributes than EEPROM. 2. Configuration. Any nonvolatile memory can retain a configuration. However, if the configuration changes and power failure is a possibility, the higher write endurance of FRAM allows changes to be recorded without restriction. Any time the system state is altered, the change can be written. This avoids writing to memory on power down when the available time is short and power scarce. 3. High noise environments. Writing to EEPROM in a noisy environment can be challenging. When severe noise or power fluctuations are present, the long write time of EEPROM creates a window of vulnerability during which the write can be 9 May 2001 A S Slave Address 1 A Data Byte 1 P Data corrupted. The fast write of FRAM is complete within a microsecond. This time is typically too short for noise or power fluctuation to disturb it. 4. Time to market. In a complex system, multiple software routines may need to access the nonvolatile memory. In this environment the time delay associated with programming EEPROM adds undue complexity to the software development. Each software routine must wait for complete programming before allowing access to the next routine. 5. RF/ID. In the area of contactless memory, FRAM provides an ideal solution. Since RF/ID memory is powered by an RF field, the long programming time and high current consumption needed to write EEPROM is unattractive. FRAM provides a superior solution. The FM24CL64 is suitable for multi-chip RF/ID products. 6. Maintenance tracking. In sophisticated systems, the operating history and system state during a failure is important knowledge. Maintenance can be expedited when this information has been recorded. Due to the high write endurance, FRAM makes an ideal system log. In addition, the convenient 2-wire interface of the FM24CL64 allows memory to be distributed throughout the system using minimal additional resources. 7/7 Ramtron FM24CL64 Electrical Specifications Absolute Maximum Ratings Description Ambient storage or operating temperature Voltage on any pin with respect to ground D.C. output current on any pin Lead temperature (Soldering, 10 seconds) Ratings -40°C to + 85°C -1.0V to +5.0V 5 mA 300° C Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only, and the functional operation of the device at these or any other conditions above those listed in the operational section of this specification is not implied. Exposure to absolute maximum ratings conditions for extended periods may affect device reliability. DC Operating Conditions TA = -40° C to + 85° C, VDD =2.7V to 3.65V unless otherwise specified Symbol Parameter Min Typ Max Units Notes VDD Main Power Supply 2.7 3.65 V 1 2 IDD VDD Supply Current 75 @ SCL = 100 kHz µA 150 @ SCL = 400 kHz µA 400 @ SCL = 1 MHz µA ISB Standby Current 1 3 µA ILI Input Leakage Current 10 4 µA ILO Output Leakage Current 10 4 µA VIL Input Low Voltage -0.3 VDD x 0.3 V 1,5 VIH Input High Voltage VDD x 0.7 VDD + 0.5 V 1,5 VOL Output Low Voltage 0.4 V 1 @ IOL = 3.0 mA ZI Input impedance of 50 6 KΩ WP, A0-2 1 MΩ VHYS Input Hysteresis VDD x .05 V 1, 5 Notes 1. Referenced to VSS. 2. SCL toggling between VDD-0.3V and VSS, other inputs VSS or VDD-0.3V 3. SCL = SDA = VDD. All inputs VSS or VDD. Stop command issued. 4. VIN or VOUT = VSS to VDD. Does not apply to pins with pull down resistors. 5. This parameter is characterized but not tested. 6. The input pull-down circuit is strong (50KΩ) when the input voltage is below VIL and weak (1MΩ) when the input voltage is above VIH. 9 May 2001 8/8 Ramtron FM24CL64 AC Parameters TA = -40° C to + 85° C, VDD =2.7V to 3.65V unless otherwise specified Symbol Parameter Min Max Min Max Min Max fSCL SCL Clock Frequency 0 100 0 400 0 1000 tLOW Clock Low Period 4.7 1.3 0.6 tHIGH Clock High Period 4.0 0.6 0.4 tAA SCL Low to SDA Data Out Valid 3 0.9 0.55 tBUF tHD:STA tSU:STA tHD:DAT tSU:DAT tR tF tSU:STO tDH tSP Bus Free Before New Transmission Start Condition Hold Time Start Condition Setup for Repeated Start Data In Hold Data In Setup Input Rise Time Input Fall Time Stop Condition Setup Data Output Hold (from SCL @ VIL) Noise Suppression Time Constant on SCL, SDA Units kHz µs µs µs 4.7 1.3 0.5 µs 4.0 4.7 0.6 0.6 0.25 0.25 µs µs 0 250 0 100 0 100 300 100 ns ns ns ns µs ns 50 ns 1000 300 4.0 0 300 300 0.6 0 50 0.25 0 50 Notes 1 2 2 Notes : All SCL specifications as well as start and stop conditions apply to both read and write operations. 1 The speed-related specifications are guaranteed characteristic points along a continuous curve of operation from D.C. to 1 MHz. 2 This parameter is periodically sampled and not 100% tested. Capacitance TA = 25° C, f=1.0 MHz, VDD = 3V Symbol Parameter Max CI/O Input/output capacitance (SDA) 8 CIN Input capacitance 6 Units pF pF Notes 1 1 Notes 1 This parameter is periodically sampled and not 100% tested. AC Test Conditions Input Pulse Levels Input rise and fall times Input and output timing levels VDD * 0.1 to VDD * 0.9 10 ns VDD*0.5 Equivalent AC Load Circuit 3.65V 1100 Ω Output 100 pF 9 May 2001 9/9 Ramtron FM24CL64 Diagram Notes All start and stop timing parameters apply to both read and write cycles. Clock specifications are identical for read and write cycles. Write timing parameters apply to slave address, word address, and write data bits. Functional relationships are illustrated in the relevant data sheet sections. These diagrams illustrate the timing parameters only. Read Bus Timing tR ` tF tHIGH tSP tLOW tSP SCL tSU:SDA 1/fSCL tBUF tHD:DAT tSU:DAT SDA Start tDH tAA Stop Start Acknowledge Write Bus Timing t HD:DAT SCL tHD:STA t SU:STO t SU:DAT tAA SDA Start Stop Start Acknowledge Data Retention TA = -40° C to + 85° C, VDD = 2.7V to 3.65V unless otherwise specified Parameter Min Units Notes Data Retention 10 Years 1 Endurance 1E16 Cycles 2 Notes 1. Data retention is specified at 85° C. 2. Endurance is the guaranteed number of read- or write-cycles per address that can be performed while maintaining the specified data retention. It should be impossible to reach this limit for most applications. 9 May 2001 10/10 Ramtron FM24CL64 8-pin SOP JEDEC MS-012 Index Area E H Pin 1 h D 45 ° A e B α .10 mm .004 in. A1 L C Selected Dimensions Refer to JEDEC MS-012 for complete dimensions and notes. Controlling dimensions is in millimeters. Conversions to inches are not exact. Symbol A A1 B C D E e H h L α 9 May 2001 Dim mm in. mm in. mm in. mm in. mm in. mm in. mm in. mm in. mm in. mm in. Min 1.35 .053 .10 .004 .33 .013 .19 .007 4.80 .189 3.80 .150 Nom. Max 1.75 .069 .25 .010 .51 .020 .25 .010 5.00 .197 4.00 .157 1.27 BSC .050 BSC 5.80 .228 .25 .010 .40 .016 0° 6.20 .244 .50 .197 1.27 .050 8° 11/11