X5083
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 7). 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 format-
ted as follows.
Status Register/Block Lock/WDT Byte
7
0
Block Lock Memory
Xicor’s block lock memory provides a flexible mecha-
nism to store and lock system ID and parametric infor-
mation. There are seven distinct block lock memory
areas within the array which vary in size from one page
to as much as half of the entire array. These areas and
associated address ranges are block locked by writing
the appropriate two byte block lock instruction to the
device as described in Table 1 and Figure 9. Once a
block lock instruction has been completed, that block
lock setup is held in the nonvolatile status register until
the next block lock instruction is issued. The sections
of the memory array that are block locked can be read
but not written until block lock is removed or changed.
6
0
5
0
4
WD1
3
WD0
2
BL2
1
BL1
0
BL0
Table 1. Instruction Set and Block Lock Protection Byte Definition
Instruction Format
0000 0110
0000 0100
0000 0001
Instruction Name and Operation
WREN: set the write enable latch (write enable operation)
WRDI: reset the write enable latch (write disable operation)
Write status instruction—followed by:
Block lock/WDT byte: (See Figure 1)
--->none of the array
000WD
1
WD
2
000 --->no block lock: 00h-00h
000WD
1
WD
2
001 --->block lock Q1: 0000h-00FFh --->lower quadrant (Q1)
000WD
1
WD
2
010 --->block lock Q2: 0100h-01FFh --->Q2
000WD
1
WD
2
011 --->block lock Q3: 0200h-02FFh --->Q3
000WD
1
WD
2
100 --->block lock Q4: 0300h-03FFh --->upper quadrant (Q4)
000WD
1
WD
2
101 --->block lock H1: 0000h-01FFh --->lower half of the array (H1)
000WD
1
WD
2
110 --->block lock P0: 0000h-000Fh --->lower page (P0)
000WD
1
WD
2
111 --->block lock Pn: 03F0h-03FFh --->upper page (PN)
READ STATUS: reads status register & provides write in progress status on SO pin
WRITE: write operation followed by address and data
READ: read operation followed by address
0000 0101
0000 0010
0000 0011
Watchdog Timer
The watchdog timer bits, WD0 and WD1, select the
watchdog time out period. These nonvolatile bits are
programmed with the WRSR instruction. A change to
the Watchdog Timer, either setting a new time out
period or turning it off or on, takes effect, following
either the next command (read or write) or cycling the
power to the device.
The recommended procedure for changing the Watch-
dog Timer settings is to do a WREN, followed by a
write status register command. Then execute a soft-
ware loop to read the status register until the MSB of
the status byte is zero. A valid alternative is to do a
REV 1.1.6 6/25/02
WREN, followed by a write status register command.
Then wait 10ms and do a read status command.
Table 2. Watchdog Timer Definition
Status Register Bits
WD1
0
0
1
1
WD0
0
1
0
1
Watchdog Time Out
(Typical)
1.4 seconds
600 milliseconds
200 milliseconds
disabled (factory default)
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Characteristics subject to change without notice.
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XICOR [ XICOR INC. ]
