ICmic TM This X25642 device has been acquired by IC MICROSYSTEMS from Xicor, Inc. IC MICROSYSTEMS X25642 64K 2 8K x 8 Bit TM Advanced SPI Serial E PROM with Block Lock FEATURES •2MHz Clock Rate •Low Power CMOS —<1µA Standby Current —<5mA Active Current •2.7V To 5.5V Power Supply •SPI Modes (0,0 & 1,1) •8K X 8 Bits —32 Byte Page Mode •Block Lock Protection 2 —Protect 1/4, 1/2 or all of E PROM Array •Built-in Inadvertent Write Protection —Power-Up/Down protection circuitry —Write Enable Latch —Write Protect Pin •Self-Timed Write Cycle —5ms Write Cycle Time (Typical) •High Reliability —Endurance: 100,000 cycles —Data Retention: 100 Years —ESD protection: 2000V on all pins •Packages —8-Lead PDIP —8-Lead SOIC —14-Lead SOIC —20-Lead TSSOP Protection DESCRIPTION 2 The X25642 is a CMOS 65,536-bit serial E PROM, internally organized as 8K x 8. The X25642 features a 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 X25642 also features two additional inputs that provide the end user with added flexibility. By asserting the HOLD input, the X25642 will ignore transitions on its inputs, thus allowing the host to service higher priority interrupts. The WP input can be used as a hardwire input to the X25642 disabling all write 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 X25642 utilizes Xicor’s proprietary Direct WriteTM cell, providing a minimum endurance of 100,000 cycles and a minimum data retention of 100 years. FUNCTIONAL DIAGRAM STATUS REGISTER WRITE PROTECT LOGIC X DECODE LOGIC 8K BYTE ARRAY 64 64 X 256 SO SI COMMAND DECODE SCK 64 AND CONTROL LOGIC CS HOLD 64 X 256 128 128 X 256 WRITE CONTROL AND TIMING LOGIC WP 32 8 Y DECODE DATA REGISTER TM Direct Write TM and Block Lock Protection ©Xicor, Inc. 1994, 1995, 1996 Patents Pending 3132-1.0 1/17/97 T5/C0/D1 SH 3132 ILL F01.1 is a trademark of Xicor, Inc. 1 Characteristics subject to change without notice X25642 X25642 status register. If the internal write cycle has already been initiated, WP going LOW will have no affect on a write. PIN DESCRIPTIONS Serial Output (SO) 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. The WP pin function is blocked when the WPEN bit in the status register is “0”. This allows the user to install the X25642 in a system with WP pin grounded and still be able to write to the status register. The WP pin functions will be enabled when the WPEN bit is set “1”. 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. Hold (HOLD) 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 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. PIN CONFIGURATION Not to Scale SOIC/DIP Chip Select (CS) When CS is HIGH, the X25642 is deselected and the SO output pin is at high impedance and unless an internal write operation is underway, the X25642 will be in the standby power mode. CS LOW enables the X25642, 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. CS 1 .197" SO 2 SOIC Only WP 3 VSS 4 X25642 8 VCC 7 HOLD 6 SCK 5 SI .244" SOIC Write Protect (WP) .345" When WP is LOW and the nonvolatile bit WPEN is “1”, nonvolatile writes to the X25642 status register are disabled, but the part otherwise functions normally. When WP is held HIGH, all functions, including nonvolatile writes operate normally. WP going LOW while CS is still LOW will interrupt a write to the NC 1 14 NC CS* 2 13 NC CS* 3 12 VCC SO 4 X25642 11 WP 5 10 VSS 6 9 SI NC 7 8 NC HOLD SCK .244" TSSOP PIN NAMES Symbol Description NC 1 20 20 NC CS 2 19 19 VCC CS Chip Select Input NC 3 18 18 NC SO Serial Output SO 4 17 17 HOLD Serial Input NC 5 16 16 NC NC 6 X25642 15 15 NC WP 7 14 14 SCK VSS 8 13 13 SI NC 9 12 12 NC NC 10 11 11 NC SI SCK .300" Serial Clock Input WP Write Protect Input VSS Ground VCC Supply Voltage HOLD Hold Input NC No Connect .252" 7037 FRM T01 3132 ILL F02.5 * Pin 2 and Pin 3 are internally connected. Only one CS needs to be connected externally. 2 X25642 Status Register The RDSR instruction provides access to the status register. The status register may be read at any time, even during a write cycle. The status register is formatted as follows: 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. PRINCIPLES OF OPERATION 7 6 5 4 3 2 1 WPEN X X X BP1 BP0 WEL 0 WIP 7037 FRM T02 The X25642 is a 8K x 8 E2PROM designed to interface directly with the synchronous serial peripheral interface (SPI) of many popular microcontroller families. WPEN, BP0 and BP1 are set by the WRSR instruction. WEL and WIP are read-only and automatically set by other operations. The X25642 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 WP inputs must be HIGH during the entire operation. The Write-In-Process (WIP) bit indicates whether the X25642 is busy with a write operation. When set to a “1”, a write is in progress, when set to a “0”, no write is in progress. During a write, all other bits are set to “1”. Table 1 contains a list of the instructions and their opcodes. All instructions, addresses and data are transferred MSB first. The Write Enable Latch (WEL) bit indicates the status of the “write 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 X25642 into a “PAUSE” condition. After releasing HOLD, the X25642 will resume operation from the point when HOLD was first asserted. The Block Protect (BP0 and BP1) bits are nonvolatile and allow the user to select one of four levels of protection. The X25642 is divided into four 16384-bit segments. One, two, or all four of the segments may be protected. That is, the user may read the segments but will be unable to alter (write) data within the selected segments. The partitioning is controlled as illustrated below. Write Enable Latch The X25642 contains a “write enable” latch. This latch must be SET before a write operation will be completed internally. The WREN instruction will set the latch and the WRDI instruction will reset the latch. This latch is automatically reset upon a power-up condition and after the completion of a byte, page, or status register write cycle. Status Register Bits Array Addresses Protected BP1 BP0 0 0 None 0 1 $1800–$1FFF 1 0 $1000–$1FFF 1 1 $0000–$1FFF 7037 FRM T03 Table 1. Instruction Set Instruction Name Instruction Format* Operation WREN 0000 0110 Set the Write Enable Latch (Enable Write Operations) WRDI 0000 0100 Reset the Write Enable Latch (Disable Write Operations) RDSR 0000 0101 Read Status Register WRSR 0000 0001 Write Status Register READ 0000 0011 Read Data from Memory Array beginning at selected address WRITE 0000 0010 Write Data to Memory Array beginning at Selected Address (1 to 32 Bytes) 7037 FRM T04 *Instructions are shown MSB in leftmost position. Instructions are transferred MSB first. 3 X25642 To read the status register the CS line is first pulled LOW to select the device followed by the 8-bit RDSR instruction. After the RDSR opcode is sent, the contents of the status register are shifted out on the SO line. Figure 2 illustrates the read status register sequence. Write-Protect Enable The Write-Protect-Enable (WPEN) is available for the X25642 as a nonvolatile enable bit for the WP pin. WPEN WP WEL Protected Unprotected Status Blocks Blocks Register 0 X 0 Protected Protected Protected 0 X 1 Protected Writable Writable 1 LOW 0 Protected Protected Protected 1 LOW 1 Protected Writable Protected X HIGH 0 Protected Protected Protected X HIGH 1 Protected Writable Writable Write Sequence Prior to any attempt to write data into the X25642, the “write enable” latch must first be set by issuing the WREN instruction (See Figure 3). CS is first taken LOW, then the WREN instruction is clocked into the X25642. After all eight bits of the instruction are transmitted, CS must then be taken HIGH. If the user continues the write operation without taking CS HIGH after issuing the WREN instruction, the write operation will be ignored. 7037 FRM T05 The Write Protect (WP) pin and the nonvolatile Write Protect Enable (WPEN) bit in the Status Register control the programmable hardware write protect feature. Hardware write protection is enabled when WP pin is LOW, and the WPEN bit is “1”. Hardware write protection is disabled when either the WP pin is HIGH or the WPEN bit is “0”. When the chip is hardware write protected, nonvolatile writes are disabled to the Status Register, including the Block Protect bits and the WPEN bit itself, as well as the block-protected sections in the memory array. Only the sections of the memory array that are not block-protected can be written. To write data to the E2PROM memory array, the user issues the WRITE instruction, followed by the address and then the data to be written. This is minimally a thirty-two clock operation. CS must go LOW and remain LOW for the duration of the operation. The host may continue to write up to 32 bytes of data to the X25642. The only restriction is the 32 bytes must reside on the same page. If the address counter reaches the end of the page and the clock continues, the counter will “roll over” to the first address of the page and overwrite any data that may have been written. Note: Since the WPEN bit is write protected, it cannot be changed back to a “0”, as long as the WP pin is held LOW. For the write operation (byte or page write) to be completed, CS can only be brought HIGH after bit 0 of data byte N is clocked in. If it is brought HIGH at any other time the write operation will not be completed. Refer to Figures 4 and 5 below for a detailed illustration of the write sequences and time frames in which CS going HIGH are 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. To write to the status register, the WRSR instruction is followed by the data to be written. Data bits 0, 1, 4, 5 and 6 must be “0”. Figure 6 illustrates this sequence. Read Sequence When reading from the E2PROM memory array, CS is first pulled LOW to select the device. The 8-bit READ instruction is transmitted to the X25642, followed by the 16-bit address of which the last 13 are used. 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 ($1FFF) 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 E2PROM array operation sequence illustrated in Figure 1. While the write is in progress following a status register or E2PROM write sequence, the status register may be read to check the WIP bit. During this time the WIP 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 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. 4 X25642 Data Protection The following circuitry has been included to prevent inadvertent writes: • The “write enable” latch is reset upon power-up. • A WREN instruction must be issued to set the “write enable” latch. • CS must come HIGH at the proper clock count in order to start a write cycle. Operational Notes The X25642 powers-up in the following state: • The device is in the low power standby state. • A HIGH to LOW transition on CS is required to enter an active state and receive an instruction. • SO pin is high impedance. • The “write enable” latch is reset. Figure 1. Read E2PROM 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 3 2 1 0 MSB 3132 ILL F03.1 Figure 2. Read Status Register Operation Sequence CS 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 SCK INSTRUCTION SI DATA OUT HIGH IMPEDANCE 7 SO MSB 5 6 5 4 3 2 1 0 3132 ILL F04 X25642 Figure 3. Write Enable Latch Sequence CS 0 1 2 3 4 5 6 7 SCK SI HIGH IMPEDANCE SO 3132 ILL F05 Figure 4. Byte Write 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 31 SCK INSTRUCTION 15 14 13 SI DATA BYTE 16 BIT ADDRESS 3 2 1 0 7 6 5 4 3 2 1 0 HIGH IMPEDANCE SO 3132 ILL F06.1 6 X25642 Figure 5. Page Write Operation 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 2 DATA BYTE 3 1 0 7 6 5 4 3 2 DATA BYTE N 1 0 6 5 4 3 2 1 0 3132 ILL F07 Figure 6. Write 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 3132 ILL F08.1 7 X25642 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 (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 indicated 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 Temperature Min. Max. Commercial 0°C +70°C Industrial –40°C +85°C Military –55°C +125°C Supply Voltage Limits X25642 5V ±10% X25642-2.7 2.7V to 5.5V 7037 FRM T07 7037 FRM T06 D.C. OPERATING CHARACTERISTICS (Over the recommended operating conditions unless otherwise specified.) Symbol Limits Min. Max. Parameter Units Test Conditions ICC VCC Supply Current (Active) 5 mA SCK = VCC x 0.1/VCC x 0.9 @ 2MHz, ISB VCC Supply Current (Standby) 1 µA ILI Input Leakage Current 10 µA CS = VCC, VIN = VSS or VCC – 0.3V VIN = VSS to VCC VOUT = VSS to VCC ILO Output Leakage Current 10 µA VIL(1) Input LOW Voltage –1 VCC x 0.3 V VIH(1) Input HIGH Voltage VCC x 0.7 VCC + 0.5 V VOL1 Output LOW Voltage 0.4 V IOL = 3mA, VCC = 5V VOH1 Output HIGH Voltage V IOH = –1.6mA, VCC = 5V VOL2 Output LOW Voltage V IOL = 1.5mA, VCC = 3V VOH2 Output HIGH Voltage V IOH = –0.4mA, VCC = 3V VCC–0.8 0.4 VCC–0.3 7037 FRM T08 POWER-UP TIMING Symbol Max. Units TPUR(3) Power-up to Read Operation Parameter Min. 1 ms TPUW(3) Power-up to Write Operation 1 ms 7037 FRM T09 CAPACITANCE TA = +25°C, f = 1MHz, VCC = 5V Symbol Max. Units Test Conditions CI/O(3) Output Capacitance (SO) Parameter 8 pF VI/O = 0V CIN(3) Input Capacitance (SCK, SI, CS, WP, HOLD) 6 pF VIN = 0V 7037 FRM T10 Notes: (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 V CC is stable until the specified operation can be initiated. These parameters are periodically sampled and not 100% tested. 8 X25642 EQUIVALENT A.C. LOAD CIRCUIT 5V A.C. CONDITIONS OF TEST Input Pulse Levels 3V VCC x 0.1 to VCC x 0.9 Input Rise and Fall Times 1.44KΩ 1.64KΩ OUTPUT 1.95KΩ 10ns Input and OutputTiming Levels OUTPUT 100pF VCC X 0.5 7037 FRM T11 4.63KΩ 100pF 3132 ILL F09.2 A.C. OPERATING CHARACTERISTICS Data Input Timing Symbol Parameter Min. Max. Units 0 2 MHz fSCK Clock Frequency tCYC Cycle Time 500 ns tLEAD CS Lead Time 250 ns tLAG CS Lag Time 250 ns tWH Clock HIGH Time 200 ns tWL Clock LOW Time 200 ns tSU Data Setup Time 50 ns tH Data Hold Time 50 ns tRI(4) tFI(4) Data In Rise Time 2 µs Data In Fall Time 2 µs tHD HOLD Setup Time 100 tCD HOLD Hold Time 100 ns tCS CS Deselect Time 2.0 µs tWC(5) Write Cycle Time ns 10 ms 7037 FRM T12 Data Output Timing Symbol Parameter Min. Max. Units 0 2 MHz fSCK Clock Frequency tDIS Output Disable Time 250 ns tV Output Valid from Clock LOW 200 ns tHO Output Hold Time tRO(4) tFO(4) tLZ(4) tHZ(4) Output Rise Time 100 ns Output Fall Time 100 ns 0 ns HOLD HIGH to Output in Low Z 100 ns HOLD LOW to Output in High Z 100 ns 7037 FRM T13 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 write cycle. 9 X25642 Serial Output Timing CS tCYC tWH tLAG SCK tV SO SI tHO MSB OUT tWL MSB–1 OUT tDIS LSB OUT ADDR LSB IN 3132 ILL F10.1 Serial Input Timing tCS CS tLEAD tLAG SCK tSU SI tH tRI MSB IN tFI LSB IN HIGH IMPEDANCE SO 3132 ILL F11 10 X25642 Hold Timing CS tHD tCD tCD tHD SCK tHZ tLZ SO SI HOLD 3132 ILL F12.1 11 X25642 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 X25642 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 X25642 PACKAGING INFORMATION 14-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) 0.020 (0.51) 0.336 (8.55) 0.345 (8.75) (4X) 7° 0.053 (1.35) 0.069 (1.75) 0.004 (0.10) 0.010 (0.25) 0.050 (1.27) 0.050" Typical 0.010 (0.25) X 45° 0.020 (0.50) 0° – 8° 0.050" Typical 0.0075 (0.19) 0.010 (0.25) 0.250" 0.016 (0.41) 0.037 (0.937) FOOTPRINT 0.030" Typical 14 Places NOTE: ALL DIMENSIONS IN INCHES (IN PARENTHESES IN MILLIMETERS) 3926 FHD F10 14 X25642 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 X25642 ORDERING INFORMATION X25642 P T G -V Vcc Limits Blank = 5V ±10% 2.7 = 2.7 to 5.5V Device G = RoHS Compliant Lead-Free package Blank = Standard package. Non lead-free Temperature Range Blank = Commercial = 0°C to +70°C I = Industrial = –40°C to +85°C M = Military = –55°C to +125° Package P = 8-Lead Plastic DIP S = 14-Lead SOIC S8 = 8-Lead SOIC V = 20-Lead TSSOP Part Mark Convention X25642 XG P = 8-Lead Plastic DIP S = 14-Lead SOIC Blank = 8 Lead SOIC V = 20-Lead TSSOP G = RoHS compliant lead free X Blank = 5V ±10%, 0°C to +70°C I = 5V ±10%, –40°C to +85°C M = 5V ±10%, –55°C to +125°C F = 2.7V to 5.5V, 0°C to 70°C G = 2.7V 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 back-up 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