Pre-Production FM25256 256Kb FRAM Serial 5V Memory Features 256K bit Ferroelectric Nonvolatile RAM • Organized as 32,768 x 8 bits • Unlimited Read/Write Cycles • 10 Year Data Retention • NoDelay™ Writes • Advanced High-Reliability Ferroelectric Process Very Fast Serial Peripheral Interface - SPI • Up to 25 MHz Frequency • Direct Hardware Replacement for EEPROM • SPI Mode 0 & 3 (CPOL, CPHA=0,0 & 1,1) Description The FM25256 is a 256-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. Unlike serial EEPROMs, the FM25256 performs write operations at bus speed. No write delays are incurred. The next bus cycle may commence immediately without the need for data polling. The next bus cycle may start immediately. In addition, the product offers virtually unlimited write endurance. Also, FRAM exhibits much lower power consumption than EEPROM. These capabilities make the FM25256 ideal for nonvolatile memory applications requiring frequent or rapid writes or low power operation. 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 FM25256 provides substantial benefits to users of serial EEPROM as a hardware drop-in replacement. The FM25256 uses the high-speed SPI bus, which enhances the high-speed write capability of FRAM technology. Device specifications are guaranteed over an industrial temperature range of -40°C to +85°C. This is a product in the pre-production phase of development. Device characterization is complete and Ramtron does not expect to change the specifications. Ramtron will issue a Product Change Notice if any specification changes are made. Rev. 2.0 Apr. 2005 Write Protection Scheme • Hardware Protection • Software Protection Wide Operating Range • Wide Voltage Operation 4.0V – 5.5V Industry Standard Configurations • Industrial Temperature -40°C to +85°C • 8-pin SOIC (-S) • “Green” 8-pin SOIC (-G) Pin Configuration CS SO WP 1 8 2 7 3 6 VSS 4 5 Pin Name /CS /WP /HOLD SCK SI SO VDD VSS VDD HOLD SCK SI Function Chip Select Write Protect Hold Serial Clock Serial Data Input Serial Data Output Supply Voltage (4.0 to 5.5V) Ground Ordering Information FM25256-S FM25256-G 8-pin SOIC “Green” 8-pin SOIC Ramtron International Corporation 1850 Ramtron Drive, Colorado Springs, CO 80921 (800) 545-FRAM, (719) 481-7000 www.ramtron.com Page 1 of 13 FM25256 WP Instruction Decode Clock Generator Control Logic Write Protect CS HOLD SCK 8192 x 32 FRAM Array Instruction Register Address Register Counter SI 15 8 Data I/O Register SO 3 Nonvolatile Status Register Figure 1. Block Diagram Pin Descriptions Pin Name /CS I/O Input SCK Input /HOLD Input /WP Input SI Input SO Output VDD VSS Supply Supply Rev. 2.0 Apr. 2005 Description Chip Select: This active low input activates the device. When high, the device enters low-power standby mode, ignores other inputs, and all outputs are tri-stated. When low, the device internally activates the SCK signal. A falling edge on /CS must occur prior to every op-code. Serial Clock: All I/O activity is synchronized to the serial clock. Inputs are latched on the rising edge and outputs occur on the falling edge. Since the device is static, the clock frequency may be any value between 0 and 25 MHz and may be interrupted at any time. Hold: The /HOLD pin is used when the host CPU must interrupt a memory operation for another task. When /HOLD is low, the current operation is suspended. The device ignores any transition on SCK or /CS. All transitions on /HOLD must occur while SCK is low. Write Protect: This active low pin prevents write operations to the status register only. A complete explanation of write protection is provided on pages 6 and 7. Serial Input: All data is input to the device on this pin. The pin is sampled on the rising edge of SCK and is ignored at other times. It should always be driven to a valid logic level to meet IDD specifications. * SI may be connected to SO for a single pin data interface. Serial Output: This is the data output pin. It is driven during a read and remains tristated at all other times including when /HOLD is low. Data transitions are driven on the falling edge of the serial clock. * SO may be connected to SI for a single pin data interface. Power Supply (4.0V to 5.5V) Ground Page 2 of 13 FM25256 Overview The FM25256 is a serial FRAM memory. The memory array is logically organized as 32,768 x 8 and is accessed using an industry standard Serial Peripheral Interface or SPI bus. Functional operation of the FRAM is similar to serial EEPROMs. The major difference between the FM25256 and a serial EEPROM with the same pinout is the FRAM’s superior write performance and power consumption. Memory Architecture When accessing the FM25256, the user addresses 32K locations of 8 data bits each. These data bits are shifted serially. The addresses are accessed using the SPI protocol, which includes a chip select (to permit multiple devices on the bus), an op-code, and a twobyte address. The upper bit of the address range is a “don’t care” value. The complete address of 15-bits specifies each byte address uniquely. Most functions of the FM25256 either are controlled by the SPI interface or are handled automatically by on-board circuitry. 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 SPI bus. Unlike an EEPROM, it is not necessary to poll the device for a ready condition since writes occur at bus speed. So, by the time a new bus transaction can be shifted into the device, a write operation will be complete. This is explained in more detail in the interface section. Users expect several obvious system benefits from the FM25256 due to its fast write cycle and high endurance as compared to EEPROM. In addition 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. Note that the FM25256 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 datasheet tolerances to prevent incorrect operation. It is recommended that the part is not powered down with chip enable active. Serial Peripheral Interface – SPI Bus The FM25256 employs a Serial Peripheral Interface (SPI) bus. It is specified to operate at speeds up to 25 MHz. This high-speed serial bus provides high performance serial communication to a host Rev. 2.0 Apr. 2005 microcontroller. Many common microcontrollers have hardware SPI ports allowing a direct interface. It is quite simple to emulate the port using ordinary port pins for microcontrollers that do not. The FM25256 operates in SPI Mode 0 and 3. The SPI interface uses a total of four pins: clock, data-in, data-out, and chip select. A typical system configuration uses one or more FM25256 devices with a microcontroller that has a dedicated SPI port, as Figure 2 illustrates. Note that the clock, data-in, and data-out pins are common among all devices. The Chip Select and Hold pins must be driven separately for each FM25256 device. For a microcontroller that has no dedicated SPI bus, a general purpose port may be used. To reduce hardware resources on the controller, it is possible to connect the two data pins together and tie off the Hold pin. Figure 3 shows a configuration that uses only three pins. Protocol Overview The SPI interface is a synchronous serial interface using clock and data pins. It is intended to support multiple devices on the bus. Each device is activated using a chip select. Once chip select is activated by the bus master, the FM25256 will begin monitoring the clock and data lines. The relationship between the falling edge of /CS, the clock and data is dictated by the SPI mode. The device will make a determination of the SPI mode on the falling edge of each chip select. While there are four such modes, the FM25256 supports only modes 0 and 3. Figure 4 shows the required signal relationships for modes 0 and 3. For both modes, data is clocked into the FM25256 on the rising edge of SCK and data is expected on the first rising edge after /CS goes active. If the clock starts from a high state, it will fall prior to the first data transfer in order to create the first rising edge. The SPI protocol is controlled by op-codes. These op-codes specify the commands to the device. After /CS is activated the first byte transferred from the bus master is the op-code. Following the op-code, any addresses and data are then transferred. Note that the WREN and WRDI op-codes are commands with no subsequent data transfer. Important: The /CS must go inactive after an operation is complete and before a new op-code can be issued. There is one valid op-code only per active chip select. Page 3 of 13 FM25256 SCK MOSI MISO SO SPI Microcontroller SI SCK SO CS SI SCK FM25256 FM25256 HOLD CS HOLD SS1 SS2 HOLD1 MOSI : Master Out Slave In MISO : Master In Slave Out SS : Slave Select HOLD2 Figure 2. System Configuration with SPI port P1.0 P1.1 Microcontroller SO SI SCK FM25256 CS HOLD P1.2 Figure 3. System Configuration without SPI port SPI Mode 0: CPOL=0, CPHA=0 7 6 5 4 3 2 1 0 SPI Mode 3: CPOL=1, CPHA=1 7 6 5 4 3 2 1 0 Figure 4. SPI Modes 0 & 3 Rev. 2.0 Apr. 2005 Page 4 of 13 FM25256 Power Up to First Access The FM25256 is not accessible for a period of time (10 ms) after power up. Users must comply with the timing parameter tPU, which is the minimum time from VDD (min) to the first /CS low. WREN - Set Write Enable Latch The FM25256 will power up with writes disabled. The WREN command must be issued prior to any write operation. Sending the WREN op-code will allow the user to issue subsequent op-codes for write operations. These include writing the status register and writing the memory. Data Transfer All data transfers to and from the FM25256 occur in 8-bit groups. They are synchronized to the clock signal (SCK), and they transfer most significant bit (MSB) first. Serial inputs are registered on the rising edge of SCK. Outputs are driven from the falling edge of SCK. Sending the WREN op-code causes the internal Write Enable Latch to be set. A flag bit in the status register, called WEL, indicates the state of the latch. WEL=1 indicates that writes are permitted. Attempting to write the WEL bit in the status register has no effect on the state of this bit. Completing any write operation will automatically clear the write-enable latch and prevent further writes without another WREN command. Figure 5 illustrates the WREN command bus configuration. Command Structure There are six commands called op-codes that can be issued by the bus master to the FM25256. They are listed in the table below. These op-codes control the functions performed by the memory. They can be divided into three categories. First, there are commands that have no subsequent operations. They perform a single function such as to enable a write operation. Second are commands followed by one byte, either in or out. They operate on the status register. The third group includes commands for memory transactions followed by address and one or more bytes of data. Table 1. Op-code Commands Name Description Set Write Enable Latch WREN Write Disable WRDI Read Status Register RDSR Write Status Register WRSR Read Memory Data READ WRITE Write Memory Data WRDI - Write Disable The WRDI command disables all write activity by clearing the Write Enable Latch. The user can verify that writes are disabled by reading the WEL bit in the status register and verifying that WEL=0. Figure 6 illustrates the WRDI command bus configuration. Op-code 0000 0000 0000 0000 0000 0000 0110b 0100b 0101b 0001b 0011b 0010b CS 0 1 2 3 4 5 6 7 0 1 1 0 SCK SI SO 0 0 0 0 Hi-Z Figure 5. WREN Bus Configuration Rev. 2.0 Apr. 2005 Page 5 of 13 FM25256 CS 0 1 2 3 4 5 6 7 0 1 0 0 SCK SI 0 0 0 0 Hi-Z SO Figure 6. WRDI Bus Configuration RDSR - Read Status Register The RDSR command allows the bus master to verify the contents of the Status register. Reading Status provides information about the current state of the write protection features. Following the RDSR opcode, the FM25256 will return one byte with the contents of the Status register. The Status register is described in detail in a later section. WRSR – Write Status Register The WRSR command allows the user to select certain write protection features by writing a byte to the Status register. Prior to issuing a WRSR command, the /WP pin must be high or inactive. Prior to sending the WRSR command, the user must send a WREN command to enable writes. Note that executing a WRSR command is a write operation and therefore clears the Write Enable Latch. Figure 7. RDSR Bus Configuration Figure 8. WRSR Bus Configuration Status Register & Write Protection The write protection features of the FM25256 are multi-tiered. Taking the /WP pin to a logic low state is the hardware write protect function. All write operations are blocked when /WP is low. To write the memory with /WP high, a WREN op-code must first be issued. Assuming that writes are enabled using WREN and by /WP, writes to memory are controlled by the Status register. As described above, writes to the status register are performed using the WRSR command and subject to the /WP pin. The Status register is organized as follows. Rev. 2.0 Apr. 2005 Table 2. Status Register Bit Name 7 6 5 4 3 2 1 0 WPEN 0 0 0 BP1 BP0 WEL 0 Bits 0 and 4-6 are fixed at 0 and cannot be modified. Note that bit 0 (Ready in EEPROMs) is unnecessary as the FRAM writes in real-time and is never busy. The BP1 and BP0 control software write protection features. They are nonvolatile (shaded yellow). The WEL flag indicates the state of the Write Enable Latch. Attempting to directly write the WEL bit in the status register has no effect on its state. This bit is internally set by the WREN command and cleared Page 6 of 13 FM25256 by terminating a write cycle (/CS high) or by using the WRDI command. BP1 and BP0 are memory block write protection bits. They specify portions of memory that are write protected as shown in the following table. Table 3. Block Memory Write Protection BP1 BP0 Protected Address Range 0 0 None 0 1 6000h to 7FFFh (upper ¼) 1 0 4000h to 7FFFh (upper ½) 1 1 0000h to 7FFFh (all) The BP1 and BP0 bits and the Write Enable Latch are the only mechanisms that protect the memory from writes. The remaining write protection features protect inadvertent changes to the block protect bits. Table 4. Write Protection WEL WPEN /WP 0 X X 1 0 X 1 1 0 1 1 1 Protected Blocks Protected Protected Protected Protected Memory Operation The SPI interface, which is capable of a relatively high clock frequency, highlights the fast write capability of the FRAM technology. Unlike SPI-bus EEPROMs, the FM25256 can perform sequential writes at bus speed. No page register is needed and any number of sequential writes may be performed. Write Operation All writes to the memory array begin with a WREN op-code. The next op-code is the WRITE instruction. This op-code is followed by a two-byte address value. The upper bit of the address is a “don’t care”. In total, 15-bits specify the address of the first data byte of the write operation. Subsequent bytes are data and they are written sequentially. Addresses are incremented internally as long as the bus master continues to issue clocks. If the last address of 7FFFh is reached, the counter will roll over to 0000h. Data is written MSB first. A write operation is shown in Figure 9. Unlike EEPROMs, any number of bytes can be written sequentially and each byte is written to memory immediately after it is clocked in (after the 8th clock). The rising edge of /CS terminates a WRITE op-code operation. Asserting /WP active in Rev. 2.0 Apr. 2005 The WPEN bit controls the effect of the hardware /WP pin. When WPEN is low, the /WP pin is ignored. When WPEN is high, the /WP pin controls write access to the status register. Thus the Status register is write protected if WPEN=1 and /WP=0. This scheme provides a write protection mechanism, which can prevent software from writing the memory under any circumstances. This occurs if the BP1 and BP0 are set to 1, the WPEN bit is set to 1, and /WP is set to 0. This occurs because the block protect bits prevent writing memory and the /WP signal in hardware prevents altering the block protect bits (if WPEN is high). Therefore in this condition, hardware must be involved in allowing a write operation. The following table summarizes the write protection conditions. Unprotected Blocks Protected Unprotected Unprotected Unprotected Status Register Protected Unprotected Protected Unprotected the middle of a write operation will have no effect until the next falling edge of /CS. Read Operation After the falling edge of /CS, the bus master can issue a READ op-code. Following this instruction is a twobyte address value. The upper bit of the address is a don’t care. In total, 15-bits specify the address of the first byte of the read operation. After the op-code and address are complete, the SI line is ignored. The bus master issues 8 clocks, with one bit read out for each. Addresses are incremented internally as long as the bus master continues to issue clocks. If the last address of 7FFFh is reached, the counter will roll over to 0000h. Data is read MSB first. The rising edge of /CS terminates a READ op-code operation. A read operation is shown in Figure 10. Hold The /HOLD pin can be used to interrupt a serial operation without aborting it. If the bus master pulls the /HOLD pin low while SCK is low, the current operation will pause. Taking the /HOLD pin high while SCK is low will resume an operation. The transitions of /HOLD must occur while SCK is low, but the SCK and /CS pins can toggle during a hold state. Page 7 of 13 FM25256 CS 0 1 2 3 4 5 6 7 0 1 2 14 13 3 4 6 7 0 1 2 6 5 3 4 5 6 3 2 1 7 7 SCK SI 0 0 0 Op-code 0 16-bit Address 1 0 0 0 X 11 Data In 1 MSB Hi-Z SO 12 0 LSB 7 4 MSB 0 0 LSB Figure 9. Memory Write CS 0 1 2 3 4 5 6 7 0 1 2 14 13 3 4 6 7 0 1 2 3 4 5 6 6 5 Data Out 4 3 2 1 7 7 SCK SI 0 SO 0 0 Op-code 0 Hi-Z 16-bit Address 0 0 1 1 X MSB 12 11 1 0 LSB 7 MSB 0 0 LSB Figure 10. Memory Read Rev. 2.0 Apr. 2005 Page 8 of 13 FM25256 Electrical Specifications Absolute Maximum Ratings Symbol Description VDD Power Supply Voltage with respect to VSS VIN Voltage on any pin with respect to VSS TSTG TLEAD VESD Storage Temperature Lead Temperature (Soldering, 10 seconds) Electrostatic Discharge Voltage - Human Body Model (JEDEC Std JESD22-A114-B) - Charged Device Model (JEDEC Std JESD22-C101-A) - Machine Model (JEDEC Std JESD22-A115-A) Package Moisture Sensitivity Level Ratings -1.0V to +7.0V -1.0V to +7.0V and VIN < VDD+1.0V -55°C to + 125°C 300° C 3kV 1kV 100V MSL-1 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 = 4.0V to 5.5V unless otherwise specified) Symbol Parameter Min Typ Max Units VDD Power Supply Voltage 4.0 5.5 V IDD Power Supply Current @ SCK = 1.0 MHz 0.8 mA @ SCK = 5.0 MHz 1.8 @ SCK = 25.0 MHz 7.0 ISB Standby Current 150 µA ILI Input Leakage Current ±1 µA ILO Output Leakage Current ±1 µA VIH Input High Voltage 0.7 VDD VDD + 0.5 V VIL Input Low Voltage -0.3 0.3 VDD V VOH Output High Voltage V VDD – 0.8 @ IOH = -2 mA VOL Output Low Voltage 0.4 V @ IOL = 2 mA VHYS Input Hysteresis 0.05 VDD V Notes 1. SCK toggling between VDD-0.3V and VSS, other inputs VSS or VDD-0.3V. 2. SCK = SI = /CS=VDD. All inputs VSS or VDD. 3. VSS ≤ VIN ≤ VDD and VSS ≤ VOUT ≤ VDD. 4. This parameter is characterized but not 100% tested. Rev. 2.0 Apr. 2005 Notes 1 2 3 3 4 Page 9 of 13 FM25256 AC Parameters (TA = -40°C to + 85°C, VDD = 4.0V to 5.5V, CL = 30pF) Symbol Parameter Min fCK SCK Clock Frequency 0 tCH Clock High Time 18 tCL Clock Low Time 18 tCSU Chip Select Setup 10 tCSH Chip Select Hold 10 tOD Output Disable Time tODV Output Data Valid Time tOH Output Hold Time 0 tD Deselect Time 60 tR Data In Rise Time tF Data In Fall Time tSU Data Setup Time 5 tH Data Hold Time 5 tHS /Hold Setup Time 10 tHH /Hold Hold Time 10 tHZ /Hold Low to Hi-Z tLZ /Hold High to Data Active Notes 1. 2. 3. Max 25 Units MHz ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns 15 15 50 50 20 15 Notes 1 1 2 1,3 1,3 2 2 tCH + tCL = 1/fCK. This parameter is characterized but not 100% tested. Rise and fall times measured between 10% and 90% of waveform. Power Cycle Timing (TA = -40° C to + 85° C, VDD = 4.0V to 5.5V) Symbol Parameter tPU Power Up (VDD min) to First Access (/CS low) tPD Last Access (/CS high) to Power Down (VDD min) tVR VDD Rise Time tVF VDD Fall Time Capacitance (TA = 25° C, f=1.0 MHz, VDD = 5.0V) Symbol Parameter CO Output capacitance (SO) CI Input capacitance Notes 1. This parameter is characterized and not 100% tested. 2. Slope measured at any point on VDD waveform. AC Test Conditions Input Pulse Levels Input rise and fall times Input and output timing levels Output Load Capacitance Rev. 2.0 Apr. 2005 Min - Min 10 0 50 100 Max - Max 8 6 Units ms µs µs/V µs/V Notes Units pF pF Notes 1 1 1,2 1,2 10% and 90% of VDD 5 ns 0.5 VDD 30 pF Page 10 of 13 FM25256 Serial Data Bus Timing tD CS tCSU SCK tSU tF 1/tCK tCL tR tCSH tCH tH SI tOH tODV tOD SO /Hold Timing tHS CS tHH SCK tHH tHS HOLD SO tHZ tLZ Power Cycle Timing VDD VDD min tVF tVR tPD tPU CS Data Retention (VDD = 4.0V to 5.5V) Parameter Data Retention Rev. 2.0 Apr. 2005 Min 10 Max - Units Years Notes Page 11 of 13 FM25256 Mechanical Drawing 8-pin SOIC (JEDEC MS-012 variation AA) Recommended PCB Footprint 7.70 3.90 ±0.10 3.70 6.00 ±0.20 2.00 Pin 1 0.65 1.27 4.90 ±0.10 1.27 0.33 0.51 0.25 0.50 1.35 1.75 0.10 0.25 0.10 mm 0°- 8° 0.19 0.25 45 ° 0.40 1.27 Refer to JEDEC MS-012 for complete dimensions and notes. All dimensions in millimeters. SOIC Package Marking Scheme XXXXXXX-P LLLLLLL RICYYWW Legend: XXXX= part number, P= package type LLLLLLL= lot code RIC=Ramtron Int’l Corp, YY=year, WW=work week Example: FM25256, Standard SOIC package, Year 2004, Work Week 39 FM25256-S A40003S RIC0439 Rev. 2.0 Apr. 2005 Page 12 of 13 FM25256 Revision History Revision 0.1 0.11 0.12 0.13 1.0 Date 9/9/03 12/9/03 1/7/04 4/28/04 8/16/04 1.1 3/14/05 2.0 4/5/05 Rev. 2.0 Apr. 2005 Summary Initial release. Reduced IDD spec limits. Added tVR spec, “green” package, and modified Power Cycling diagram. Changed tOD, tODV , and tLZ timing specs. Changed tVR and tVF conditions. Changed VDD range in AC Parameters table. Changed IDD limits. Added package marking scheme. Changed tODV spec. New rev. number to comply with new scheme. New part number FM25256 replaces FM25W256 since operating voltage is no longer wide (2.7V – 5.5V). Added note about powering down with /CS active (pg 3). Added ESD and package MSL ratings. Changed ISB spec. Changed to Pre-Production status. Page 13 of 13