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FM25640
64Kb FRAM Serial Memory Features
64K bit Ferroelectric Nonvolatile RAM * Organized as 8,192 x 8 bits * High Endurance 1 Trillion (1012) Read/Writes * 10 Year Data Retention * NoDelayTM Writes * Advanced high-reliability ferroelectric process Very Fast Serial Peripheral Interface - SPI * Up to 5 MHz maximum bus frequency * Direct hardware replacement for EEPROM * SPI Mode 0 & 3 (CPOL, CPHA=0,0 & 1,1) Sophisticated Write Protection Scheme * Hardware Protection * Software Protection Low Power Consumption * 10 A Standby Current Industry Standard Configuration * Industrial Temperature -40 C to +85 C * 8-pin SOIC
Description
The FM25640 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. Unlike serial EEPROMs, the FM25640 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. In addition, the product offers substantial write endurance compared with other nonvolatile memories. The FM25640 is capable of supporting up to 1012-read/write cycles -far more than most systems will require from a serial memory. These capabilities make the FM25640 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 FM25640 provides substantial benefits to users of serial EEPROM, in a hardware drop-in replacement. The FM25640 uses the high-speed SPI bus, which enhances the high-speed write capability of FRAM technology. The specifications are guaranteed over an industrial temperature range of -40C to +85C.
Pin Configuration CS SO WP VSS
1 2 3 4 8 7 6 5
VDD HOLD SCK SI
Pin Names /CS /HOLD /WP SCK SI SO VDD VSS
Function Chip Select Hold Write Protect Serial Clock Serial Data Input Serial Data Output 5V Ground
Ordering Information
FM25640-S 8-pin SOIC
This product conforms to specifications per the terms of the Ramtron standard warranty. Production processing does not necessarily include testing of all parameters. Rev. 2.1
Ramtron International Corporation 1850 Ramtron Drive, Colorado Springs, CO 80921 (800) 545-FRAM, (719) 481-7000, Fax (719) 481-7058 www.ramtron.com
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FM25640
WP CS HOLD SCK
Instruction Decode Clock Generator Control Logic Write Protect 2,048 x 32 FRAM Array
Instruction Register
Address Register Counter
13
8
Data I/O Register 3 Nonvolatile Status Register
SO
Figure 1. Block Diagram Pin Description Pin Name /CS I/O Input Pin Description Chip Select. Activates the device. When high, all outputs are tri-state and the device ignores other inputs. The part remains in a low-power standby mode. When low, the part recognizes activity on 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. The part is static so the clock frequency may be any value between 0 and 5 MHz and may be interrupted at any time. Hold. The /HOLD signal is used when the host CPU must interrupt a memory operation for another task. Taking the /HOLD signal to a low state pauses the current operation. The part ignores any transition on SCK or /CS. All transitions on /HOLD must occur while SCK is low. Write Protect. This pin prevents write operations to the status register. This is critical since other write protection features are controlled through the status register. A complete explanation of write protection is provided below. *Note that the function of /WP is different from the FM25040 where it prevents all writes to the part. 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. SO is the data output pin. It is driven actively during a read and remains tri-state at all other times including when HOLD\ is low. Data transitions are driven on the falling edge of the serial clock. * SO can be connected to SI for a single pin data interface since the part communicates in half-duplex. Supply Voltage: 5V Ground
SCK
Input
/HOLD
Input
/WP
Input
SI
Input
SO
Output
VDD VSS
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Supply Supply
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FM25640
Overview
The FM25640 is a serial FRAM memory. The memory array is logically organized as 8,192 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 FM25640 and a serial EEPROM with the same pin-out relates to its superior write performance.
Serial Peripheral Interface - SPI Bus
The FM25640 employs a Serial Peripheral Interface (SPI) bus. It is specified to operate at speeds up to 5 MHz. This high-speed serial bus provides high performance serial communication to a host 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 FM25640 operates in SPI Mode 0 and 3. The SPI interface uses a total of four pins: clock, data-in, data-out, and chip select. It is possible to connect the two data lines together. Figure 2 illustrates a typical system configuration using the FM25640 with a microcontroller that offers an SPI port. Figure 3 shows a similar configuration for a microcontroller that has no hardware support for the SPI bus. Protocol Overview The SPI interface is a synchronous serial interface using clock and data lines. 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 FM25640 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 FM25640 supports modes 0 and 3. Figure 4 shows the required signal relationships for modes 0 and 3. For both modes, data is clocked into the FM25640 on the rising edge of SCK and data is expected on the first rising edge after /CS goes active. If the clock begins from a high state, it will fall prior to beginning 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 part. 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. Certain op-codes are commands with no subsequent data transfer. 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.
Memory Architecture
When accessing the FM25640, the user addresses 8,192 locations each with 8 data bits. 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 two-byte address. The upper 3 bits of the address range are `don't care' values. The complete address of 13-bits specifies each byte address uniquely. Most functions of the FM25640 either are controlled by the SPI interface or are handled automatically by on-board circuitry. The access time for memory operation essentially is 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. 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 FM25640 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. Note that the FM25640 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.
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FM25640
SPI Microcontroller
FM25640
FM25640
MOSI : Master Out Slave In MISO : Master In Slave Out SS : Slave Select
Figure 2. System Configuration with SPI port
P1.0
P1.1
Microcontroller
FM25640
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
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Ramtron Data Transfer All data transfers to and from the FM25640 occur in 8-bit groups. They are synchronized to the clock signal (SCK) and they transfer most significant bit (MSB) first. Serial inputs are clocked in on the rising edge of SCK. Outputs are driven on the falling edge of SCK. Command Structure There are six commands called op-codes that can be issued by the bus master to the FM25640. 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, 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. Last are commands for memory transactions followed by address and one or more bytes of data. Table 1. Op-code Commands Name Description WREN Set Write Enable Latch WRDI Write Disable RDSR Read Status Register WRSR Write Status Register READ Read Memory Data WRITE Write Memory Data
FM25640 WREN - Set Write Enable Latch The FM25640 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. 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. Completing any write operation will automatically clear the write-enable latch and prevent further writes without another WREN command. Figure 4 below illustrates the WREN command bus configuration. 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 5 below illustrates the WRDI command bus configuration.
Op-code value 00000110b 00000100b 00000101b 00000001b 00000011b 00000010b
Figure 5. WREN Bus Configuration
Figure 6. WRDI Bus Configuration
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Ramtron 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 FM25640 will return one byte with the contents of the Status register. The Status register is described in detail in a later section.
FM25640 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. Note that on the FM25640, /WP only prevents writing to the Status register, not the memory array. 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. The bus configuration of RDSR and WRSR are shown below.
Figure 7. RDSR Bus Configuration
Figure 8. WRSR Bus Configuration
Status Register & Write Protection
The write protection features of the FM25640 are multi-tiered. First, a WREN op-code must be issued prior to any write operation. Assuming that writes are enabled using WREN, 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. Table 2. Status Register
Bit Name 7 WPEN 6 0 5 0 4 0 3 BP1 2 BP0 1 WEL 0 0
Writing the WEL bit in the status register has no effect. 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 1800h to 1FFFh (upper 1/4) 1 0 1000h to 1FFFh (upper 1/2) 1 1 0000h to 1FFFh (all)
Bits 0 and 4-6 are fixed at 0 and can not be modified. Note that the Ready bit in many EEPROMs is unnecessary as the FRAM writes in real-time and is never busy. The WPEN, BP1 and BP0 control write protection features. They are nonvolatile! The WEL flag indicates the state of the Write Enable Latch.
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FM25640 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. 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.
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
Unprotected Blocks Protected Unprotected Unprotected Unprotected
Status Register Protected Unprotected Protected Unprotected
Memory Operation
The SPI interface, with its relatively high maximum clock frequency, highlights the fast write capability of the FRAM technology. Unlike SPI-bus EEPROMs, the FM25640 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 3-bits of the address are don't care. In total, the 13-bits specify the address of the first 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 1FFFh is reached, the counter will roll over to 0000h. Data is written MSB first. 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. 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 3-bits of the address are don't care. In total, the 13-bits specify the address of the first byte of the read operation. After the opcode 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 1FFFh 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. The bus configuration for read and write operations is shown below. Hold The /HOLD pin can be used to interrupt a serial operation without aborting it. If the bus master takes 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 pin can toggle during a hold state.
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FM25640
CS 0 SCK op-code SI SO 0 0 0 0 0 0 1 0 X MSB X X 13-bit Address 12 11 10 Data 54 1 2 3 4 5 6 7 0 1 2 3 4 5 3 4 5 6 7 0 1 2 3 4 5 6 7
4
3
2
1
0
7
6
3
2
1
0 LSB
LSB MSB
Figure 9. Memory Write
CS 0 SCK op-code SI 0 0 0 0 0 0 1 1 X MSB SO X 13-bit Address X 12 11 10 4 3 2 1 0 LSB MSB 7 6 5 Data 43 2 1 LSB 0 1 2 3 4 5 6 7 0 1 2 3 4 5 3 4 5 6 7 0 1 2 3 4 5 6 7
Figure 10. Memory Read
Endurance
Internally, a FRAM operates with a read and restore mechanism similar to a DRAM. Therefore, endurance cycles are applied for each access: read or write. The FRAM architecture is based on an array of rows and columns. Each access causes a cycle for an
entire row. Therefore, data locations targeted for substantially differing numbers of cycles should not be located within the same row. In the FM25640, there are 2048 rows each 32 bits wide. Each 4 bytes in the address mark the beginning of a new row.
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FM25640
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 systemstate 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 complete within a microsecond. This time is typically too short for noise or power fluctuations 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 FM25640, 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 FM25640 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 interface of the FM25640 allows memory to be distributed throughout the system using minimal additional resources.
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FM25640
Electrical Specifications
Absolute Maximum Ratings Symbol Description VIN, VOUT Voltage on Any Pin with Respect to VSS IIN, IOUT DC Current on Any Pin TSTG Storage Temperature TLEAD Lead Temperature (Soldering, 10 seconds)
Ratings -1.0V to VDD+1V 5 mA -55C to + 125C 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 = 4.5V to 5.5V unless otherwise specified) Symbol Parameter Min Typ Max Units Notes VDD Power Supply Voltage 4.5 5.0 5.5 V IDD VDD Supply Current mA 1 1.2 0.9 @ SCK = 1.0 MHz 2.5 1.6 @ SCK = 2.0 MHz 4.5 3.0 @ SCK = 5.0 MHz ISB Standby Current 1 10 2 A ILI Input Leakage Current 10 3 A ILO Output Leakage Current 10 3 A VIL Input Low Voltage -0.3 0.3 VDD V 4 VIH Input High Voltage 0.7 VDD VDD + 0.5 V 4 VOL Output Low Voltage 0.4 V 4 @ IOL = 2 mA VOH Output High Voltage VDD - 0.8 V 4 @ IOH = -2 mA VHYS Input Hysteresis 0.05 VDD V 4 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. VIN or VOUT = VSS to VDD 4. Characterized but not 100% tested in production.
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FM25640 AC Parameters (TA = -40 C to + 85 C, VDD = 4.5V to 5.5V unless otherwise specified) Symbol Parameter Min Max fCK SCK Clock Frequency 0 5.0 tCH Clock High Time 90 tCL Clock Low Time 90 tCSU Chip Select Setup 90 tCSH Chip Select Hold 90 tOD Output Disable 100 tODV Output Data Valid 60 tOH Output Hold 0 tD Deselect Time 100 tR Data In Rise Time 1 tF Data In Fall Time 1 tH Data Hold Time 30 tSU Data Setup Time 20 tHS /Hold Setup Time 70 tHH /Hold Hold Time 40 tHZ /Hold Low to Hi-Z 100 tLZ /Hold High to Data Active 50 Notes 1. Rise and fall times measured between 10% and 90% of waveform. 2. Characterized but not 100% tested in production. Capacitance TA = 25 C, f=1.0 MHz, VDD = 5V Symbol Parameter CO Output capacitance (SDA) CI Input capacitance 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 Equivalent AC Load Circuit
Units MHz ns ns ns ns ns ns ns ns s s ns ns ns ns ns ns
Notes
2
1,2 1,2
2 2
Max 8 6
Units pF pF
Notes 1 1
10% and 90% of VDD 10 ns VDD*0.5
Data Retention VDD = 4.5V to 5.5V unless otherwise specified Parameter Min Units Data Retention 10 Years
Notes
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FM25640 Serial Data Bus Timing
tD tCSH
tF tCSU tH 1/fCK
tR
tCL
tCH
tSU
tODV
tOH
tOD
/Hold Timing
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FM25640 8-pin SOIC - JEDEC MS-012
Index Area
E
H
Pin 1
D A e B A1 .10 mm .004 in. h 45
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 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
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FM25640
Revision History
Revision 1.0 2.0 2.1 Date 10/23/00 10/21/02 8/5/03 Summary Changed status to Preliminary. Changed status to Production. Changed endurance from 1010 to 1012 cycles. Extended storage temperature limits. Removed DIP packaging option.
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