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64K |
X25644/46 |
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8K x 8 Bit |
32K |
X25324/26 |
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4K x 8 Bit |
16K |
X25164/66 |
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2K x 8 Bit |
Programmable Watchdog Timer w/Serial E2PROM
FEATURES |
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DESCRIPTION |
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• Programmable Watchdog Timer with Reset |
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These devices combine two popular functions, Watchdog |
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Assertion |
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Timer, and Serial E2PROM Memory in one package. This |
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—Reset Signal Valid to Vcc=1V |
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combination lowers system cost, reduces board space |
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—Power Up Reset Control |
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requirements, and increases reliability. |
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• Save Critical Data With Block LockTM Protection |
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The Watchdog Timer provides an independent protection |
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—Block LockTM Protect 0, 1/4, 1/2 or all of |
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Serial E2PROM Memory Array |
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mechanism for microcontrollers. During a system failure, |
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the device will respond with a RESET/RESET signal |
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• In Circuit Programmable ROM Mode |
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after a selectable time-out interval. The user selects the |
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• Long Battery Life With Low Power Consumption |
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interval from three preset values. Once selected, the |
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—<50 A Max Standby Current, Watchdog On |
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interval does not change, even after cycling the power. |
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—<1 A Max Standby Current, Watchdog Off |
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—<5mA Max Active Current during Write |
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The memory portion of the device is a CMOS Serial |
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—<400 A Max Active Current during Read |
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E2PROM array with Xicor’s Block LockTM Protection. The |
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• 1.8V to 3.6V, 2.7V to 5.5V and 4.5V to 5.5V Power |
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array is internally organized as x 8. The device features a |
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Supply Operation |
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Serial Peripheral Interface (SPI) and software protocol |
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• 2MHz Clock Rate |
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allowing operation on a simple four-wire bus. |
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• Minimize Programming Time |
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The device utilizes Xicor’s proprietary Direct WriteTM cell, |
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—32 Byte Page Write Mode |
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—Self-Timed Write Cycle |
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providing a minimum endurance of 100,000 cycles per |
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—5ms Write Cycle Time (Typical) |
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sector and a minimum data retention of 100 years. |
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• SPI Modes (0,0 & 1,1) |
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• Built-in Inadvertent Write Protection |
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—Power-Up/Power-Down Protection Circuitry |
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—Write Enable Latch |
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—Write Protect Pin |
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• High Reliability |
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• Available Packages |
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—14-Lead SOIC (X2564x) |
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—14-Lead TSSOP (X2532x, X2516x) |
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—8-Lead SOIC (X2532x, X2516x) |
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BLOCK DIAGRAM |
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SI |
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DATA |
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PAGE DECODE LOGIC |
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SO |
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REGISTER |
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32 |
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SCK |
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COMMAND |
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X - DECODE |
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DECODE & |
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LOGIC |
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CONTROL |
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SERIAL |
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CS |
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LOGIC |
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E2PROM |
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RESET |
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STATUS |
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ARRAY |
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RESET/RESET |
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CONTROL |
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REGISTER |
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WATCHDOG |
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TIMER |
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WRITE, |
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HIGH |
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BLOCK LOCK & |
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VOLTAGE |
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WP |
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ICP ROM CONTROL |
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CONTROL |
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7029 FRM 01 |
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Xicor, Inc. 1994, 1995, 1996 Patents Pending |
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1 |
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Characteristics subject to change without notice |
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7050 -1.0 6/20/97 T0/C0/D0 SH |
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X25644/46
X25324/26
X25164/66
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.
Serial Input (SI)
SI is a 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.
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.
Chip Select (CS)
When CS is HIGH, the device is deselected and the SO output pin is at high impedance and unless a nonvolatile write cycle is underway, the device will be in the standby power mode. CS LOW enables the device’s, 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.
Write Protect (WP)
When WP is low and the nonvolatile bit WPEN is “1”, nonvolatile writes to the device’s Status Register are disabled, but the part otherwise functions normally. When
WP is held high, all functions, including nonvolatile writes to the Status Register operate normally. If an internal Status Register Write Cycle has already been initiated, WP going low while WPEN is a “1”will have no effect on this write. Subsequent write attempts to the Status Register under these conditions will be disabled.
The WP pin function is blocked when the WPEN bit in the Status Register is “0”This. allows the user to install the device in a system with WP pin grounded and still be able to program the Status Register. The WP pin functions will be enabled when the WPEN bit is set to a “1”.
Reset (RESET/RESET)
RESET/RESET is an active LOW/HIGH, open drain output which goes active whenever the Watchdog Timer is enabled and CS remains either HIGH or LOW longer than the selectable Watchdog time-out period. It will remain active for tRST, the Reset Timeout period. A falling edge of
CS will reset the Watchdog Timer.
PIN CONFIGURATION
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14-LEAD SOIC |
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Not to Scale |
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NC |
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1 |
14 |
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NC |
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VCC |
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CS |
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CS |
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VCC |
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0.345” |
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X25644/46 |
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RESET/RESET |
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SCK |
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WP |
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VSS |
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SI |
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NC |
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0.244” |
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8-LEAD SOIC |
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VCC |
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CS |
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SO |
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2 |
X25324/26 7 |
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RESET/RESET |
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0.197” |
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X25164/66 |
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WP |
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SCK |
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VSS |
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SI |
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0.244” |
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14-LEAD TSSOP |
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VCC |
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SO |
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2 |
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RESET/RESET |
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NC |
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3 X25324/28 12 |
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NC |
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0.200” |
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NC |
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4 X25164/66 11 |
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NC |
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NC |
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5 |
10 |
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NC |
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6 |
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SCK |
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WP |
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VSS |
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8 |
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SI |
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0.177” |
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7036 FRM 02 |
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PIN NAMES
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Symbol |
Description |
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Chip Select Input |
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CS |
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SO |
Serial Output |
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SI |
Serial Input |
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SCK |
Serial Clock Input |
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Write Protect Input |
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WP |
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VSS |
Ground |
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VCC |
Supply Voltage |
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Reset Output |
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RESET/RESET |
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7029 FRM T01
2
X25644/46
X25324/26
X25164/66
PRINCIPLES OF OPERATION
The device is designed to interface directly with the synchronous Serial Peripheral Interface (SPI) of many popular microcontroller families.
The device monitors the bus and asserts RESET/RESET output if there is no bus activity within user programmable time-out period. The device contains an 8-bit instruction register. It is accessed via the SI input, with data being clocked in on the rising edge of SCK. CS must be LOW during the entire operation.
All instructions (Table 1), addresses and data are transferred MSB first. Data input on the SI line is latched on the first rising edge of SCK after CS goes LOW. Data is output on the SO line by the falling edge of SCK. SCK is static, allowing the user to stop the clock and then start it again to resume operations where left off.
Write Enable Latch
The device contains a Write Enable Latch. This latch must be SET before a Write Operation is initiated. The WREN instruction will set the latch and the WRDI instruction will reset the latch (Figure 3). This latch is automatically reset upon a power-up condition and after the completion of a valid Write Cycle.
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:
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
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WPEN |
FLB |
WD1 |
WD0 |
BL1 |
BL0 |
WEL |
WIP |
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7029 FRM T02
The Write-In-Progress (WIP) bit is a volatile, read only bit and indicates whether the device is busy with an internal nonvolatile write operation. The WIP bit is read using the RDSR instruction. When set to a “1”, a nonvolatile write operation is in progress. When set to a “0”, no write is in progress.
The Write Enable Latch (WEL) bit indicates the Status of the Write Enable Latch. When WEL=1, the latch is set HIGH and when WEL=0 the latch is reset LOW. The WEL bit is a volatile, read only bit. It can be set by the WREN instruction and can be reset by the WRDI instruction.
The Block Lock bits, BL0 and BL1, set the level of Block LockTM Protection. These nonvolatile bits are programmed using the WRSR instruction and allow the user to protect one quarter, one half, all or none of the E2PROM array. Any portion of the array that is Block Lock Protected can be read but not written. It will remain protected until the BL bits are altered to disable Block Lock Protection of that portion of memory.
Status |
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Register |
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Bits |
Array Addresses Protected |
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BL1 |
BL0 |
X2564x |
X2532x |
X2516x |
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0 |
0 |
None |
None |
None |
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0 |
1 |
$1800–$1FFF |
$0C00–$0FFF |
$0600–$07FF |
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1 |
0 |
$1000–$1FFF |
$0800–$0FFF |
$0400–$07FF |
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1 |
1 |
$0000–$1FFF |
$0000–$0FFF |
$0000–$07FF |
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7029 FRM T03
Table 1. Instruction Set
Instruction Name |
Instruction Format* |
Operation |
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WREN |
0000 0110 |
Set the Write Enable Latch (Enable Write Operations) |
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SFLB |
0000 0000 |
Set Flag Bit |
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WRDI/RFLB |
0000 0100 |
Reset the Write Enable Latch/Reset Flag Bit |
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RSDR |
0000 0101 |
Read Status Register |
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WRSR |
0000 0001 |
Write Status Register(Watchdog, BlockLock & WPEN Bits) |
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READ |
0000 0011 |
Read Data from Memory Array Beginning at Selected Address |
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WRITE |
0000 0010 |
Write Data to Memory Array Beginning at Selected Address |
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*Instructions are shown MSB in leftmost position. Instructions are transferred MSB first. |
7029 FRM T04 |
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3 |
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X25644/46
X25324/26
X25164/66
The Watchdog Timer bits, WD0 and WD1, select the Watchdog Time-out Period. These nonvolatile bits are programmed with the WRSR instruction.
Status Register Bits |
Watchdog Time-out |
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WD1 |
WD0 |
(Typical) |
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0 |
0 |
1.4 Seconds |
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0 |
1 |
600 Milliseconds |
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1 |
0 |
200 Milliseconds |
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1 |
1 |
Disabled |
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7029 FRM T05
The FLAG bit shows the status of a volatile latch that can be set and reset by the system using the SFLB and RFLB instructions. The Flag bit is automatically reset upon power up.
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 E2PROM Array Sequence (Figure 1).
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. Refer to the Read Status Register Sequence (Figure 2).
Write Sequence
The nonvolatile WPEN bit is programmed using the WRSR instruction. This bit works in conjunction with the WP pin to provide Programmable Hardware Write Protection (Table 2). When WP is LOW and the WPEN bit is programmed HIGH, all Status Register Write Operations are disabled.
In Circuit Programmable ROM Mode
This mechanism protects the Block Lock and Watchdog bits from inadvertant corruption. It may be used to perform an In Circuit Programmable ROM function by hardwiring the WP pin to ground, writing and Block Locking the desired portion of the array to be ROM, and then programming the WPEN bit HIGH.
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 device, followed by the 16bit address. After the READ opcode and address are
Prior to any attempt to write data into the device, the “Write Enable” Latch (WEL) must first be set by issuing the WREN instruction (Figure 3). CS is first taken LOW, then the WREN instruction is clocked into the device. 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.
To write data to the E2PROM memory array, the user then issues the WRITE instruction followed by the 16 bit address and then the data to be written. Any unused address bits are specified to be “0’s”. The WRITE operation minimally takes 32 clocks. CS must go low and remain low for the duration of the operation. If the address counter reaches the end of a page and the clock continues, the counter will roll back to the first address of the page and overwrite any data that may have been previously written.
Table 2. Block Protect Matrix
STATUS |
STATUS |
DEVICE |
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REGISTER |
REGISTER |
PIN |
BLOCK |
BLOCK |
REGISTER |
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PROTECTED |
UNPROTECTED |
WPEN, BL0, BL1 |
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WEL |
WPEN |
WP# |
BLOCK |
BLOCK |
WD0, WD1 BITS |
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0 |
X |
X |
Protected |
Protected |
Protected |
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1 |
1 |
0 |
Protected |
Unprotected |
Protected |
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1 |
0 |
X |
Protected |
Unprotected |
Unprotected |
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1 |
X |
1 |
Protected |
Unprotected |
Unprotected |
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7029 FRM T06
4
X25644/46
X25324/26
X25164/66
For the Page Write Operation (byte or page write) to be completed, CS can only be brought HIGH after bit 0 of the last data byte to be written is clocked in. If it is brought HIGH at any other time, the write operation will not be completed (Figure 4).
To write to the Status Register, the WRSR instruction is followed by the data to be written (Figure 5). Data bits 0 and 1 must be “0”.
While the write is in progress following a Status Register or E2PROM Sequence, the Status Register may be read to check the WIP bit. During this time the WIP bit will be high.
RESET/RESET Operation
The RESET (X25xx4) output is designed to go LOW whenever the Watchdog timer has reached its programmable time-out limit.
The RESET (X25xx6) output is designed to go HIGH whenever the watchdog timer has reached its programmable time-out limit.
The RESET/RESET output is an open drain output and requires a pull up resistor.
Operational Notes
The device 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.
•The Flag Bit is reset.
•Reset Signal is active for tPURST
Data Protection
The following circuitry has been included to prevent inadvertent writes:
•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 nonvolatile write cycle.
Figure 1. Read E2PROM Array Sequence
CS |
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0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
20 |
21 |
22 |
23 |
24 |
25 |
26 |
27 |
28 |
29 |
30 |
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SCK |
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INSTRUCTION |
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16 BIT ADDRESS |
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SI |
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15 |
14 |
13 |
3 |
2 |
1 |
0 |
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HIGH IMPEDANCE |
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DATA OUT |
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7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
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SO |
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MSB |
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7029 FRM 03 |
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5