FM24CL04 4Kb FRAM Serial Memory Features 4K bit Ferroelectric Nonvolatile RAM • Organized as 512 x 8 bits • Unlimited Read/Writes • 10 Year Data Retention • NoDelay™ Writes • Advanced High-Reliability Ferroelectric Process Fast Two-wire Serial Interface • Up to 1 MHz maximum bus frequency • Direct hardware replacement for EEPROM Description The FM24CL04 is a 4-kilobit nonvolatile memory employing an advanced ferroelectric process. A ferroelectric random access memory or FRAM is nonvolatile and performs reads and writes like 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. Low Power Operation • 2.7V to 3.65V operation • 75 µA Active Current (100 kHz) @ 3V • 1 µA Standby Current Industry Standard Configuration • Industrial Temperature -40° C to +85° C • 8-pin SOIC Pin Configuration NC A1 A2 1 8 2 7 3 6 VSS 4 5 VDD WP SCL SDA Unlike serial EEPROMs, the FM24CL04 performs write operations at bus speed. No write delays are incurred. Data is written to the memory array in the cycle after it has been successfully transferred to the device. The next bus cycle may commence immediately. These capabilities make the FM24CL04 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. The FM24CL04 provides substantial benefits to users of serial EEPROM, yet these benefits are available in a hardware drop-in replacement. The FM24CL04 is available in an industry standard 8-pin package using a two-wire protocol. The specifications are guaranteed over an industrial temperature range of 40°C to +85°C. This product conforms to specifications per the terms of the Ramtron standard warranty. Production processing does not necessarily include testing of all parameters. Pin Names A1-A2 SDA SCL WP VSS VDD Function Device Select Address 1 and 2 Serial Data/Address Serial Clock Write Protect Ground Supply Voltage 3V Ordering Information FM24CL04-S 8-pin SOIC Ramtron International Corporation 1850 Ramtron Drive, Colorado Springs, CO 80921 (800) 545-FRAM, (719) 481-7000, Fax (719) 481-7058 www.ramtron.com Rev. 2.0 July 2003 Page 1 of 12 FM24CL04 Address Latch Counter 128 x 32 FRAM Array 8 SDA ` Serial to Parallel Converter Data Latch SCL WP A1 A2 Control Logic Figure 1. Block Diagram Pin Description Pin Name A1-A2 I/O Input SDA I/O SCL Input WP Input NC VDD VSS Supply Supply Pin Description Address 1-2: The address pins set the device select address. The device address value in the 2-wire slave address must match the setting of these two pins. These pins are internally pulled down. Serial Data/Address: This is a bi-directional pin used to shift serial data and addresses for the two-wire interface. It employs an open-drain output and is intended to be wireOR’d 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 input for the two-wire interface. Data is clocked out of the device on the SCL falling edge, and clocked in on the SCL rising edge. The SCL input also incorporates a Schmitt trigger input for improved noise immunity. Write Protect: When WP is high the entire array is write protected. When WP is low, all addresses may be written. This pin is internally pulled down. No connect Supply Voltage Ground Rev. 2.0 July 2003 Page 2 of 12 FM24CL04 Overview Two-wire Interface The FM24CL04 is a serial FRAM memory. The memory array is logically organized as 512 x 8 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 FM24CL04 and a serial EEPROM with the same pinout relates to its superior write performance. The FM24CL04 employs a bi-directional two-wire bus protocol using few pins and little board space. Figure 2 illustrates a typical system configuration using the FM24CL04 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 FM24CL04, the user addresses 512 locations each with 8 data bits. These data bits are shifted serially. The 512 addresses are accessed using the two-wire protocol, which includes a slave address (to distinguish other devices), a page address, and a word address. The word address consists of 8bits that specify one of 256 addresses. The page address is 1-bit and so there are 2 pages each of 256 locations. The complete address of 9-bits specifies each byte address uniquely. Most functions of the FM24CL04 either are controlled by the two-wire interface or are handled automatically by on-board circuitry. 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 can expect several obvious system benefits from the FM24CL04 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 FM24CL04 is always a slave device. The bus protocol is controlled by transition states in the SDA and SCL signals. There are four conditions: Start, Stop, Data bit, and Acknowledge. Figure 3 illustrates the signal conditions that specify the four states. Detailed timing diagrams are shown in the electrical specifications. VDD Rmin = 1.1 KΩ Rmax = tR/Cbus Microcontroller SDA SCL SDA SCL FM24CL04 FM24CL64 A1 A2 A0 A1 A2 Figure 2. Typical System Configuration Note that the FM24CL04 contains no power management circuits other than a simple internal power-on reset. It is the user’s responsibility to ensure that VDD is within data sheet tolerances to prevent incorrect operation. Rev. 2.0 July 2003 Page 3 of 12 FM24CL04 Figure 3. Data Transfer Protocol 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 must end with a Stop condition. If an operation is pending 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. Start Condition A Start condition is indicated when the bus master drives SDA from high to low while the SCL signal is high. All read and write transactions begin with 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 FM24CL04 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. 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 NoAcknowledge and the operation is aborted. The receiver could fail to acknowledge for two distinct reasons. First, if a byte transfer fails, the NoAcknowledge ends the current operation so that the device can be addressed again. This allows the last byte to be recovered in the event of a communication error. Second and most common, the receiver does not acknowledge the data to deliberately end an operation. For example, during a read operation, the FM24CL04 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 FM24CL04 to attempt to drive the bus on the next clock while the master is sending a new command such as a Stop command. Slave Address The first byte that the FM24CL04 expects after a start condition is the slave address. As shown in Figure 4, the slave address contains the device type, the device select, the page of memory to be accessed, 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 FM24CL04. The device type allows other types of functions to reside on the 2-wire bus within an identical address range. Bits 3-2 are the device address. If bit 3 matches the A2 pin and bit 2 matches the A1 pin the device will be selected. Bit 1 is the page select. It specifies the 256-byte block of memory that is targeted for the current operation. Bit 0 is the read/write bit. A 0 indicates a write operation. Word Address After the FM24CL04 (as receiver) acknowledges the slave ID, the master will place the word address on the bus for a write operation. The word address is the lower 8-bits of the address to be combined with the 1-bit page select to specify exactly the byte to be written. The complete 9-bit address is latched internally. Rev. 2.0 July 2003 Page 4 of 12 FM24CL04 Memory Operation Figure 4. Slave Address No word address occurs for a read operation. Reads always use the lower 8-bits that are held internally in the address latch and the 9th address bit is part of the slave address. Reads always begin at the address following the previous access. A random read address can be loaded by doing a write operation as explained below. After transmission of each data byte, just prior to the acknowledge, the FM24CL04 increments the internal address latch. This allows the next sequential byte to be accessed with no additional addressing. After the last address (1FFh) is reached, the address latch will roll over to 000h. There is no limit to the number of bytes that can be accessed with a single read or write operation. Data Transfer After all address information has been transmitted, data transfer between the bus master and the FM24CL04 can begin. For a read operation the FM24CL04 will place 8 data bits on the bus then wait for an acknowledge. If the acknowledge occurs, the next sequential byte will be transferred. If the acknowledge is not sent, the read operation is concluded. For a write operation, the FM24CL04 will accept 8 data bits from the master then send an acknowledge. All data transfer occurs MSB (most significant bit) first. The FM24CL04 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 FM24CL04 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 slave address then a word address. The bus master indicates a write operation by setting the LSB of the Slave 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 1FFh to 000h. Unlike other nonvolatile memory technologies, there is no write delay with FRAM. 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 done condition. An actual memory array 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 a start or stop condition prior to the 8th data bit. The FM24CL04 needs no page buffering. Pulling write protect high will disable writes to the entire array. The FM24CL04 will not acknowledge data bytes that are written when write protect is asserted. In addition, the address counter will not increment if writes are attempted. Pulling WP low (VSS) will deactivate this feature. Figure 5 below illustrates both a single- and multiple- byte write. Rev. 2.0 July 2003 Page 5 of 12 FM24CL04 Start By Master S Address & Data Slave Address 0 A Word Address By FM24CL04 Stop A Data Byte A P Acknowledge Figure 5. Byte Write By Master Start S Address & Data Slave Address 0 A Word Address Stop A By FM24CL04 Data Byte A Data Byte A P Acknowledge Figure 6. Multiple Byte Write 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 FM24CL04 uses the internal address latch to supply the lower 8 address bits. In a selective read, the user performs a procedure to set these lower address bits to a specific value. Current Address & Sequential Read The FM24CL04 uses an internal latch to supply the lower 8 address bits for a read operation. A current address read uses the existing value in the address latch as a starting place for the read operation. This is the address immediately following that of the last operation. To perform a current address read, the bus master supplies a slave address with the LSB set to 1. This indicates that a read operation is requested. The page select bit in the slave address specifies the block of memory that is used for the read operation. After the acknowledge, the FM24CL04 will begin shifting out data from the current address. The current address is the bit from the slave address combined with the 8 bits that were 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 FM24CL04 should read out the next sequential byte. There are four ways to properly terminate a read operation. Failing to properly terminate the read will most likely create a bus contention as the FM24CL04 attempts to read out additional data onto the bus. The four valid methods are as follows. 1. 2. 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 the preferred method. 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. Bus contention may result. The bus master issues a start in the 9th clock cycle. Bus contention may result. If the internal address reaches 1FFh it will wrap around to 000h on the next read cycle. Figures 7 and 8 show the proper operation for current address reads. Selective (Random) Read A simple technique allows a user to select a random address location as the starting point for a read operation. This involves using the first two bytes of a write operation to set the internal address byte followed by subsequent read operations. To perform a selective read, the bus master sends out the slave address with the LSB set to 0. This specifies a write operation. According to the write protocol, the bus master then sends the word address byte that is loaded into the internal address latch. After the FM24CL04 acknowledges the word address, the bus master issues a start condition. This simultaneously aborts the write operation and allows the read command to be issued with the slave address LSB set to a 1. The operation is now a current address read. See Figure 9. Rev. 2.0 July 2003 Page 6 of 12 FM24CL04 Figure 7. Current Address Read Figure 8. Sequential Read Figure 9. Selective (Random) Read Rev. 2.0 July 2003 Page 7 of 12 FM24CL04 Applications The versatility of FRAM technology fits into many diverse 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. The attributes of fast writes and high write endurance combine in many innovative 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 corrupted. The fast write of FRAM is completed 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. When time to market is critical, FRAM can eliminate this simple obstacle. As soon as a write is issued to the FM24CL04, it is effectively done -- no waiting. 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 FM24CL04 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 FM24CL04 allows memory to be distributed throughout the system using minimal additional resources. Rev. 2.0 July 2003 Page 8 of 12 FM24CL04 Electrical Specifications Absolute Maximum Ratings Symbol VDD VIN TSTG TLEAD Description Power Supply Voltage with respect to VSS Voltage on any signal pin with respect to VSS Storage Temperature Lead Temperature (Soldering, 10 seconds) Ratings -1.0V to +5.0V -1.0V to +5.0V and VIN < VDD+1.0V * -55°C to + 125°C 300° C * Exception: The “VIN < VDD+1.0V” restriction does not apply to the SCL and SDA inputs. 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 VDD IDD ISB ILI ILO VIH VIL VOL RIN VHYS Parameter Main Power Supply VDD Supply Current @ SCL = 100 kHz @ SCL = 400 kHz @ SCL = 1 MHz Standby Current Input Leakage Current Output Leakage Current Input High Voltage Input Low Voltage Output Low Voltage @ IOL = 3.0 mA Input Resistance (WP, A2, A1) For VIN = VIL (max) For VIN = VIH (min) Input Hysteresis Min 2.7 Typ Max 3.65 Units V 75 150 300 1 10 10 VDD + 0.5 0.3 VDD 0.4 µA µA µA µA µA µA V V V Notes 1 0.7 VDD -0.3 50 1 0.05 VDD KΩ MΩ V 2 3 3 4 4 5 4 Notes 1. SCL toggling between VDD-0.3V and VSS, other inputs VSS or VDD-0.3V 2. SCL = SDA = VDD. All inputs VSS or VDD. Stop command issued. 3. VIN or VOUT = VSS to VDD 4. This parameter is periodically sampled and not 100% tested. Rev. 2.0 July 2003 Page 9 of 12 FM24CL04 AC Parameters (TA = -40° C to + 85° C, VDD = 2.7V to 3.65V, CL = 100 pF unless otherwise specified) Symbol fSCL tLOW tHIGH tAA Parameter SCL Clock Frequency Clock Low Period Clock High Period SCL Low to SDA Data Out Valid Min 0 4.7 4.0 tBUF 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 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 tHD:STA tSU:STA tHD:DAT tSU:DAT tR tF tSU:STO tDH tSP Max 100 Min 0 1.3 0.6 3 Min 0 0.6 0.4 0.9 1000 300 4.0 0 Max 400 0.55 300 300 0.6 0 50 Max 1000 0.25 0 50 Units kHz µs µs µs Notes 1 1 Notes : All SCL specifications as well as start and stop conditions apply to both read and write operations. 1 This parameter is periodically sampled and not 100% tested. Capacitance (TA = 25° C, f=1.0 MHz, VDD = 3V) Symbol CI/O CIN Parameter Input/output capacitance (SDA) Input capacitance Max 8 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 0.1 VDD to 0.9 VDD 10 ns 0.5 VDD Equivalent AC Load Circuit Rev. 2.0 July 2003 Page 10 of 12 FM24CL04 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 Write Bus Timing Data Retention (VDD = 2.7V to 3.65V unless otherwise specified) Parameter Min Units Data Retention 10 Years Notes 1 Notes 1. The relationship between retention, temperature, and the associated reliability level is characterized separately. Rev. 2.0 July 2003 Page 11 of 12 FM24CL04 8-pin SOIC (JEDEC Standard MS-012 variation AA) Controlling dimensions in millimeters. Conversions to inches are not exact. Symbol Dim Min Nom. A mm 1.35 in. 0.053 A1 mm 0.10 in. 0.004 B mm 0.33 in. 0.013 C mm 0.19 in. 0.007 D mm 4.80 in. 0.189 E mm 3.80 in. 0.150 e mm 1.27 BSC in. 0.050 BSC H mm 5.80 in. 0.228 h mm 0.25 in. 0.010 L mm 0.40 in. 0.016 α 0° Max 1.75 0.069 0.25 0.010 0.51 0.020 0.25 0.010 5.00 0.197 4.00 0.157 6.20 0.244 0.50 0.197 1.27 0.050 8° Rev. 2.0 July 2003 Page 12 of 12