APPLICATION NOTE A V A I L A B L E AN61 • AN75 • AN77 • AN79 • AN82 X25F064/032/016/008 SerialFlash™ Memory With Block LockTM Protection FEATURES DESCRIPTION • 1MHz Clock Rate • SPI Serial Interface • 64K/32K/16K/8K Bits — 32 Byte Small Sector Program Mode • Low Power CMOS — <1µA Standby Current — <5mA Active Current • 1.8V – 3.6V or 5V “Univolt” Read and Program Power Supply Versions • Block Lock Protection — Protect 1/4, 1/2, or all of E2PROM Array • Built-in Inadvertent Program Protection — Power-Up/Power-Down protection circuitry — Program Enable Latch — Program Protect Pin • Self-Timed Program Cycle — 5ms Program Cycle Time (Typical) • High Reliability — Endurance: 100,000 cycles per byte — Data Retention: 100 Years — ESD protection: 2000V on all pins • 8-Lead PDlP Package • 8-Lead 150 mil SOIC Packages • 32K, 16K, 8K available in 14-Lead TSSOP, 64K available in 20-Lead TSSOP The X25F064/032/016/008 family are 8/16/32/64K-bit CMOS SerialFlash memory, internally organized X 8. They feature a “Univolt” Program and Read voltage, Serial Peripheral Interface (SPI), and software protocol allowing operation on a simple three-wire bus. The bus signals are a clock input (SCK), plus separate data in (SI) and data out (SO) lines. Access to the device is controlled through a chip select (CS) input, allowing any number of devices to share the same bus. The X25F064/032/016/008 also features two additional inputs that provide the end user with added flexibility. By asserting the HOLD input, the X25F064/032/016/008 will ignore transitions on its inputs, thus allowing the host to service higher priority interrupts. The PP input can be used as a hardwire input to the X25F064/032/016/008 disabling all program attempts to the status register, thus providing a mechanism for limiting end user capability of altering 0, 1/4, 1/2, or all of the memory. The X25F064/032/016/008 utilizes Xicor’s proprietary flash cell, providing a minimum endurance of 100,000 cycles and a minimum data retention of 100 years. FUNCTIONAL DIAGRAM DATA REGISTER SI SECTOR DECODE LOGIC SO SCK 32 COMMAND DECODE AND CONTROL LOGIC X DECODE LOGIC 8 MEMORY ARRAY CS STATUS REGISTER HOLD PP PROGRAMMING CONTROL LOGIC HIGH VOLTAGE CONTROL 6685 ILL F01.4 SerialFlash™ and Block Lock™ Protection are trademarks of Xicor, Inc. © Xicor, Inc. 1995, 1996 Patents Pending 6685-3.1 8/29/96 T3/C0/D0 SH Characteristics subject to change without notice X25F064/032/016/008 PIN DESCRIPTIONS Hold (HOLD) Serial Output (SO) HOLD is used in conjunction with the CS pin to select the device. Once the part is selected and a serial sequence is underway, HOLD may be used to pause the serial communication with the controller without resetting the serial sequence. To pause, HOLD must be brought LOW while SCK is LOW. To resume communication, HOLD is brought HIGH, again while SCK is LOW. If the pause feature is not used, HOLD should be held HIGH at all times. SO is a push-pull serial data output pin. During a read cycle, data is shifted out on this pin. Data is clocked out by the falling edge of the serial clock. Serial Input (SI) SI is the serial data input pin. All opcodes, byte addresses, and data to be written to the memory are input on this pin. Data is latched by the rising edge of the serial clock. PIN CONFIGURATION Serial Clock (SCK) The Serial Clock controls the serial bus timing for data input and output. Opcodes, addresses, or data present on the SI pin are latched on the rising edge of the clock input, while data on the SO pin change after the falling edge of the clock input. 8-Lead DIP/SOIC CS 1 SO 2 X25F064/ 7 032/016/ 3 6 008 4 5 PP VSS Chip Select (CS) 8 14-Lead TSSOP When CS is HIGH, the X25F064/032/016/008 is deselected and the SO output pin is at high impedance and unless an internal program operation is underway the X25F064/032/016/008 will be in the standby power mode. CS LOW enables the X25F064/032/016/008, placing it in the active power mode. It should be noted that after power-up, a HIGH to LOW transition on CS is required prior to the start of any operation. HOLD SCK SI 20-Lead TSSOP CS 1 14 VCC NC 1 20 NC SO 2 13 HOLD CS 2 19 VCC NC 3 12 NC NC 3 18 NC NC 4 NC SO 4 17 HOLD NC NC 5 16 NC NC X25F032/ 016/008 11 5 10 PP 6 9 SCK NC 6 15 NC VSS 7 8 SI PP 7 14 SCK VSS 8 13 SI NC 9 12 NC NC 10 11 NC Program Protect (PP) When PP is LOW and the nonvolatile bit PPEN is “1”, nonvolatile programming of the X25F064/032/016/008 status register is disabled, but the part otherwise functions normally. When PP is held HIGH, all functions, including nonvolatile programming operate normally. PP going LOW while CS is still LOW will interrupt programming of the X25F064/032/016/008 status register. If the internal program cycle has already been initiated, PP going LOW will have no effect on programming. VCC X25F064 6685 ILL F02.4 PIN NAMES The PP pin function is blocked when the PPEN bit in the status register is “0”. This allows the user to install the X25F064/032/016/008 into a system with PP pin grounded and still be able to program the status register. The PP pin functions will be enabled when the PPEN bit is set “0”. SYMBOL DESCRIPTION CS SO SI SCK PP VSS VCC HOLD NC Chip Select Input Serial Output Serial Input Serial Clock Input Program Protect Input Ground Supply Voltage Hold Input No Connect 6685 PGM T01.1 2 X25F064/032/016/008 PRINCIPLES OF OPERATION formatted as follows: The X25F064/032/016/008 family are SerialFlash Memory designed to interface directly with the synchronous serial peripheral interface (SPI) of many popular microcontroller families. 7 PPEN 6 X 5 X 4 X 3 BL1 2 BL0 1 PEL 0 PIP 6685 PGM T02.2 PPEN, BL0, and BL1 are set by the PRSR instruction. PEL and PIP are “read-only” and automatically set by other operations. The X25F064/032/016/008 family contains an 8-bit instruction register. It is accessed via the SI input, with data being clocked in on the rising SCK. CS must be LOW and the HOLD and PP inputs must be HIGH during the entire operation. The PP input is “Don’t Care” if PPEN is set “0”. The Programming-In-Process (PIP) bit indicates whether the X25F064/032/016/008 device is busy with a program operation. When set to a “1” programming is in progress, when set to a “0” no programming is in progress. During programming, all other bits are set to “1”. Table 1 contains a list of the instructions and their operation codes. All instructions, addresses and data are transferred MSB first. The Program Enable Latch (PEL) bit indicates the status of the program enable latch. When set to a “1” the latch is set; when set to a “0” the latch is reset. Data input is sampled on the first rising edge of SCK after CS goes LOW. SCK is static, allowing the user to stop the clock and then resume operations. If the clock line is shared with other peripheral devices on the SPI bus, the user can assert the HOLD input to place the X25F064/ 032/016/008 into a “PAUSE” condition. After releasing HOLD, the X25F064/032/016/008 device will resume operation from the point when HOLD was first asserted. The Block Lock (BL0 and BL1) bits are nonvolatile and allow the user to select one of four levels of protection. The X25F064/032/016/008 device array is divided into four equal segments. One, two, or all four of the segments may be locked. That is, the user may read the segments, but will be unable to alter (program) data within the selected segments. The partitioning is controlled as illustrated below. Program Enable Latch The X25F064/032/016/008 device contains a program enable latch. This latch must be SET before a program operation will be completed internally. The PREN instruction will set the latch and the PRDI instruction will reset the latch. This latch is automatically reset on power-up and after the completion of a sector program or status register write cycle. Status Register Bits BL1 BL0 0 0 1 1 0 1 0 1 Array Addresses Locked None upper fourth upper half All 6685 PGM T03.1 Status Register Program-Protect Enable The RDSR instruction provides access to the status register. The status register may be read at any time, even during a program cycle. The status register is The Program-Protect-Enable bit (PPEN) in the X25F064/032/016/008 status register acts as an enable bit for the PP pin. Table 1. Instruction Set Instruction Name PREN PRDI RDSR PRSR READ Instruction Format* 0000 0110 0000 0100 0000 0101 0000 0001 0000 0011 PROGRAM 0000 0010 Operation Set the Program Enable Latch (Enable Program Operations) Reset the Program Enable Latch (Disable Program Operations) Read Status Register Program Status Register Read from Memory Array beginning at Selected Address Program Memory Array beginning at Selected Address (32 Bytes) 6685 PGM T04.2 *Instructions are shown MSB in leftmost position. Instructions are transferred MSB first. 3 X25F064/032/016/008 PPEN PP 0 0 1 1 X X X X LOW LOW HIGH HIGH Locked PEL Blocks 0 1 0 1 0 1 Unlocked Blocks tion. After the read status register opcode is sent, the contents of the status register are shifted out on the SO line. The Read Status Register Sequence is illustrated in Figure 2. Status Register Locked Locked Locked Locked Programmable Programmable Locked Locked Locked Locked Programmable Locked Locked Locked Locked Locked Programmable Programmable Programming Sequence Prior to any attempt to program the X25F064/032/016/ 008 device, the program enable latch must first be set by issuing the PREN instruction (See Figure 3). CS is first taken LOW, then the PREN instruction is clocked into the X25F064/032/016/008 device. After all eight bits of the instruction are transmitted, CS must then be taken HIGH. If the user continues the programming operation without taking CS HIGH after issuing the PREN instruction, the programming operation will be ignored. 6685 PGM T05.2 The Program Protect (PP) pin and the nonvolatile Program Protect Enable (PPEN) bit in the Status Register control the programmable hardware write protect feature. Hardware program protection is enabled when PP pin is LOW, and the PPEN bit is “1”. Hardware program protection is disabled when either the PP pin is HIGH or the PPEN bit is “0”. When the chip is hardware program protected, nonvolatile programming of the Status Register in disabled, including the Block Lock bits and the PPEN bit itself, as well as the Block Lock sections in the memory array. Only the sections of the memory array that are not Block Locked can be programmed. Note: To program the SerialFlash memory array, the user issues the PROGRAM instruction, followed by the address of the first location in the sector and then the data to be programmed. The data is programmed in a 256clock operation. CS must go LOW and remain LOW for the duration of the operation. The 32 bytes must reside in the same sector and cannot cross sector boundaries. If the address counter reaches the end of the sector and the clock continues, or if fewer than 32 bytes are clocked in, the contents of the sector cannot be guaranteed. Since the PPEN bit is program protected, it cannot be changed back to a “0”, as long as the PP pin is held LOW. For the program operation to be completed, CS can only be brought HIGH after bit 0 of data byte 32 is clocked in. If it is brought HIGH at any other time the program operation will not be completed. Refer to Figure 4 below for a detailed illustration of the programming sequence and time frames in which CS going HIGH is valid. Clock and Data Timing Data input on the SI line is latched on the rising edge of SCK. Data is output on the SO line by the falling edge of SCK. Read Sequence To program the status register, the PRSR instruction is followed by the data to be programmed. Data bits 0, 1, 4, 5 and 6 must be “0”. This sequence is shown in Figure 5. When reading from the SerialFlash memory array, CS is first pulled LOW to select the device. The 8-bit READ instruction is transmitted to the X25F064/032/016/008 device, followed by the 16-bit address. After the read opcode and address are sent, the data stored in the memory at the selected address is shifted out on the SO line. The data stored in memory at the next address can be read sequentially by continuing to provide clock pulses. The address is automatically incremented to the next higher address after each byte of data is shifted out. When the highest address is reached the address counter rolls over to address $0000, allowing the read cycle to be continued indefinitely. The read operation is terminated by taking CS HIGH. Refer to the Read SerialFlash Memory Array Operation Sequence illustrated in Figure 1. While the program cycle is in progress, following a status register or memory write sequence, the status register may be read to check the PIP bit. During this time the PIP bit will be HIGH. Hold Operation The HOLD input should be HIGH (at VIH) under normal operation. If a data transfer is to be interrupted HOLD can be pulled LOW to suspend the transfer until it can be resumed. The only restriction is that the SCK input must be LOW when HOLD is first pulled LOW and SCK must also be LOW when HOLD is released. The HOLD input may be tied HIGH either directly to VCC or tied to VCC through a resistor. To read the status register, the CS line is first pulled LOW to select the device followed by the 8-bit instruc4 X25F064/032/016/008 Operational Notes Data Protection The device powers-up in the following state: The following circuitry has been included to prevent inadvertent programming: • The device is in the low power standby state. • The program enable latch is reset upon power-up. • A HIGH to LOW transition on CS is required to enter an active state and receive an instruction. • A program enable instruction must be issued to set the program enable latch. • SO pin is high impedance. • CS must come HIGH at the proper clock count in order to start a program cycle. • The program enable latch is reset. Figure 1. Read SerialFlash Memory Array Operation Sequence CS 0 1 2 3 4 5 6 7 8 9 10 20 21 22 23 24 25 26 27 28 29 30 SCK INSTRUCTION 16 BIT ADDRESS 15 14 13 SI 3 2 1 0 DATA OUT HIGH IMPEDANCE 7 SO 6 5 4 MSB CS 1 2 3 4 5 6 7 8 9 10 11 12 13 14 7 6 5 SCK INSTRUCTION SI DATA OUT HIGH IMPEDANCE SO MSB 5 4 3 2 2 1 0 6685 ILL F03 Figure 2. Read Status Register Operation Sequence 0 3 1 0 6685 ILL F04 X25F064/032/016/008 Figure 3. Program Enable Latch Sequence CS 0 1 2 3 4 5 6 7 SCK INSTRUCTION SI SO HIGH IMPEDANCE 6685 ILL F05.1 6 X25F064/032/016/008 Figure 4. Programming Sequence CS 0 1 2 3 4 5 6 7 8 9 20 21 22 23 24 25 26 27 28 29 30 31 10 SCK INSTRUCTION DATA BYTE 1 16 BIT ADDRESS 15 14 13 SI 3 2 1 7 0 6 5 4 3 2 1 0 CS 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 SCK DATA BYTE 2 SI 7 6 5 4 3 DATA BYTE 3 2 1 0 7 6 5 4 3 DATA BYTE 32 2 1 0 6 5 4 3 2 1 0 6685 ILL F07.1 Figure 5. Program Status Register Operation Sequence CS 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 SCK DATA BYTE INSTRUCTION 7 SI 6 5 4 3 2 1 0 HIGH IMPEDANCE SO 6685 ILL F08 7 X25F064/032/016/008 ABSOLUTE MAXIMUM RATINGS* Temperature Under Bias .................. –65°C to +135°C Storage Temperature ....................... –65°C to +150°C Voltage on any Pin with Respect to VSS ......... –1V to +7V D.C. Output Current ............................................. 5mA Lead Temperature (Soldering, 10 Seconds) ............................. 300°C *COMMENT 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 sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. RECOMMENDED OPERATING CONDITIONS Temp Commercial Extended Industrial Min. 0°C –20°C –40°C Supply Voltage X25F064/032/016/008 X25F064/032/016/008–5 Max. +70°C +85°C +85°C Limits 1.8V to 3.6V 4.5V to 5.5V 6685 PGM T07.3 6685 PGM T06.2 D.C. OPERATING CHARACTERISTICS (Over the recommended operating conditions unless otherwise specified.) Limits Symbol Parameter Min. Max. Units 5 mA ICC VCC Supply Current (Active) ISB1(2) ISB2 ILI ILO VIL(1) VIH(1) VOL1 VOH1 VOL2 VOH2 VCC Supply Current (Standby) 1 VCC Supply Current (Standby) 10 Input Leakage Current 10 Output Leakage Current –1 10 Input LOW Voltage VCC x 0.7 VCC x 0.3 Input HIGH Voltage VCC + 0.5 Output LOW Voltage 0.4 Output HIGH Voltage VCC – 0.3 Output LOW Voltage 0.4 Output HIGH Voltage VCC – 0.8 µA µA µA µA V V V V V V Test Conditions SCK = VCC x 0.1/VCC x 0.9 @ 1MHz, SO = Open, CS = VSS CS = VCC, VIN = VSS or VCC, VCC = 3.6V CS = VCC, VIN = VSS or VCC, VCC = 5V VIN = VSS to VCC VOUT = VSS to VCC IOL = 1.5mA, VCC = 2.7V IOH = –0.4mA, VCC = 2.7V IOL = 3mA, VCC = 5V IOH = –1.6mA, VCC = 5V 6685 PGM T08.4 POWER-UP TIMING Symbol tPUR(3) Parameter Power-up to Read Operation tPUW(3) Power-up to Write Operation Min. Max. 1 Units ms 5 ms 6685 PGM T09 CAPACITANCE TA = 25°C, f = 1MHz, VCC = 5V. Symbol COUT(2) CIN(2) Notes: Test Output Capacitance (SO) Input Capacitance (SCK, SI, CS, WP, HOLD) Max. 8 6 Units pF pF Conditions VOUT = 0V VIN = 0V 6685 PGM T10.1 (1) VIL min. and VIH max. are for reference only and are not tested. (2) This parameter is periodically sampled and not 100% tested. (3) tPUR and tPUW are the delays required from the time VCC is stable until the specified operation can be initiated. These parameters are periodically sampled and not 100% tested. 8 X25F064/032/016/008 EQUIVALENT A.C. LOAD CIRCUIT Input Pulse Levels VCC x 0.1 to VCC x 0.9 Input Rise and Fall Times 10ns Input and Output Timing Level VCC x 0.5 5V 2.7V 1.44KΩ 1.64KΩ 6685 PGM T11 OUTPUT OUTPUT 4.63KΩ A.C. TEST CONDITIONS 100pF 1.95KΩ 100pF 6685 ILL F09.3 A.C. CHARACTERISTICS (Over recommended operating conditions, unless otherwise specified) Data Input Timing Symbol fSCK tCYC tLEAD tLAG tWH tWL tSU tH tRI(4) tFI(4) tHD tCD tCS tPC(5) Parameter Clock Frequency Cycle Time CS Lead Time CS Lag Time Clock HIGH Time Clock LOW Time Data Setup Time Data Hold Time Data In Rise Time Data In Fall Time HOLD Setup Time HOLD Hold Time CS Deselect Time Program Cycle Time Min. 0 1000 500 500 400 400 100 100 Max. 1 2 2 200 200 2 10 Units MHz ns ns ns ns ns ns ns µs µs ns ns µs ms 6685 PGM T12.3 Data Output Timing Symbol fSCK tDIS tV tHO tRO(4) tFO(4) tLZ(4) tHZ(4) Parameter Clock Frequency Output Disable Time Output Valid from Clock LOW Output Hold Time Output Rise Time Output Fall Time HOLD HIGH to Output in Low Z HOLD LOW to Output in High Z Min. Max. Units 0 1 500 400 MHz ns ns ns ns ns ns ns 0 300 300 100 100 6685 PGM T13.2 Notes: (4) This parameter is periodically sampled and not 100% tested. (5) tWC is the time from the rising edge of CS after a valid write sequence has been sent to the end of the self-timed internal nonvolatile program cycle. 9 X25F064/032/016/008 Serial Output Timing CS tCYC tWH tLAG SCK tV SO SI tHO MSB OUT tWL tDIS MSB–1 OUT LSB OUT ADDR LSB IN 6685 ILL F10 Serial Input Timing tCS CS tLEAD tLAG SCK tSU SI tH tRI MSB IN tFI LSB IN HIGH IMPEDANCE SO 6685 ILL F11 10 X25F064/032/016/008 Hold Timing CS tHD tCD tCD tHD SCK tHZ tLZ SO SI HOLD 6685 ILL F12 11 X25F064/032/016/008 PACKAGING INFORMATION 8-LEAD PLASTIC DUAL IN-LINE PACKAGE TYPE P 0.430 (10.92) 0.360 (9.14) 0.260 (6.60) 0.240 (6.10) PIN 1 INDEX PIN 1 0.300 (7.62) REF. HALF SHOULDER WIDTH ON ALL END PINS OPTIONAL 0.145 (3.68) 0.128 (3.25) SEATING PLANE 0.025 (0.64) 0.015 (0.38) 0.065 (1.65) 0.045 (1.14) 0.150 (3.81) 0.125 (3.18) 0.020 (0.51) 0.016 (0.41) 0.110 (2.79) 0.090 (2.29) 0.015 (0.38) MAX. 0.060 (1.52) 0.020 (0.51) 0.325 (8.25) 0.300 (7.62) 0° 15° TYP. 0.010 (0.25) NOTE: 1. ALL DIMENSIONS IN INCHES (IN PARENTHESES IN MILLIMETERS) 2. PACKAGE DIMENSIONS EXCLUDE MOLDING FLASH 3926 FHD F01 12 X25F064/032/016/008 PACKAGING INFORMATION 8-LEAD PLASTIC SMALL OUTLINE GULL WING PACKAGE TYPE S 0.150 (3.80) 0.158 (4.00) 0.228 (5.80) 0.244 (6.20) PIN 1 INDEX PIN 1 0.014 (0.35) 0.019 (0.49) 0.188 (4.78) 0.197 (5.00) (4X) 7° 0.053 (1.35) 0.069 (1.75) 0.004 (0.19) 0.010 (0.25) 0.050 (1.27) 0.010 (0.25) X 45° 0.020 (0.50) 0.050" TYPICAL 0.050" TYPICAL 0° – 8° 0.0075 (0.19) 0.010 (0.25) 0.250" 0.016 (0.410) 0.037 (0.937) 0.030" TYPICAL 8 PLACES FOOTPRINT NOTE: ALL DIMENSIONS IN INCHES (IN PARENTHESES IN MILLIMETERS) 3926 FHD F22.1 13 X25F064/032/016/008 PACKAGING INFORMATION 14-LEAD PLASTIC, TSSOP PACKAGE TYPE V .025 (.65) BSC .169 (4.3) .252 (6.4) BSC .177 (4.5) .193 (4.9) .200 (5.1) .047 (1.20) .0075 (.19) .0118 (.30) .002 (.05) .006 (.15) .010 (.25) Gage Plane 0° – 8° Seating Plane .019 (.50) .029 (.75) Detail A (20X) .031 (.80) .041 (1.05) See Detail “A” NOTE: ALL DIMENSIONS IN INCHES (IN PARENTHESES IN MILLIMETERS) 3926 FHD F32 14 X25F064/032/016/008 PACKAGING INFORMATION 20-LEAD PLASTIC, TSSOP PACKAGE TYPE V .025 (.65) BSC .169 (4.3) .252 (6.4) BSC .177 (4.5) .252 (6.4) .300 (6.6) .047 (1.20) .0075 (.19) .0118 (.30) .002 (.05) .006 (.15) .010 (.25) Gage Plane 0° – 8° Seating Plane .019 (.50) .029 (.75) Detail A (20X) .031 (.80) .041 (1.05) See Detail “A” NOTE: ALL DIMENSIONS IN INCHES (IN PARENTHESES IN MILLIMETERS) 3926 FHD F45 15 X25F064/032/016/008 ORDERING INFORMATION X25FXXX P T –X VCC Range Blank = 1.8V to 3.6V 5 = 4.5V to 5.5V Device Temperature Range Blank = Commercial = 0°C to +70°C E = Extended = –20°C to +85°C I = Industrial = –40°C to +85°C Package X25F064 P = 8-Lead Plastic DIP S = 8-Lead SOIC V = 20-Lead TSSOP X25F032 X25F016 X25F008 P = 8-Lead Plastic DIP S = 8-Lead SOIC V = 14-Lead TSSOP Part Mark Convention P = 8-Lead Plastic DIP Blank = 8-Lead SOIC V = 14/20-Lead TSSOP X25FXXX X25F064 X25F032 X25F016 X25F008 X Blank = 1.8V to 3.6V, 0°C to +70°C 5 = 4.5V to 5.5V, 0°C to +70°C I5 = 4.5V to 5.5V, –40°C to +85°C LIMITED WARRANTY Devices sold by Xicor, Inc. are covered by the warranty and patent indemnification provisions appearing in its Terms of Sale only. Xicor, Inc. makes no warranty, express, statutory, implied, or by description regarding the information set forth herein or regarding the freedom of the described devices from patent infringement. Xicor, Inc. makes no warranty of merchantability or fitness for any purpose. Xicor, Inc. reserves the right to discontinue production and change specifications and prices at any time and without notice. Xicor, Inc. assumes no responsibility for the use of any circuitry other than circuitry embodied in a Xicor, Inc. product. No other circuits, patents, licenses are implied. U.S. PATENTS Xicor products are covered by one or more of the following U.S. Patents: 4,263,664; 4,274,012; 4,300,212; 4,314,265; 4,326,134; 4,393,481; 4,404,475; 4,450,402; 4,486,769; 4,488,060; 4,520,461; 4,533,846; 4,599,706; 4,617,652; 4,668,932; 4,752,912; 4,829, 482; 4,874, 967; 4,883, 976. Foreign patents and additional patents pending. LIFE RELATED POLICY In situations where semiconductor component failure may endanger life, system designers using this product should design the system with appropriate error detection and correction, redundancy and backup features to prevent such an occurrence. Xicor's products are not authorized for use in critical components in life support devices or systems. 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. 16