X5645 Datasheet, PDF (6/19 Pages) Xicor Inc. – CPU Supervisor with 64Kbit SPI EEPROM

X5643/X5645
Table 2. Block Protect Matrix
WREN CMD Status Register Device Pin
Block
Block
WEL
0
1
1
1
WPEN
X
1
0
X
WP#
X
0
X
1
Protected Block
Protected
Protected
Protected
Protected
Unprotected Block
Protected
Writable
Writable
Writable
Status Register
WPEN, BL0, BL1
WD0, WD1
Protected
Protected
Writable
Writable
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 WRDS
instruction.
The block lock bits, BL0 and BL1, set the level of block
lock protection. These nonvolatile bits are programmed
using the WRSR instruction and allow the user to pro-
tect one quarter, one half, all or none of the EEPROM
array. Any portion of the array that is block lock pro-
tected can be read but not written. It will remain pro-
tected until the BL bits are altered to disable block lock
protection of that portion of memory.
Status
Register Bits
BL1 BL0
0
0
0
1
1
0
1
1
Array Addresses Protected
X5643/X5645
None
$1800–$1FFF
$1000–$1FFF
$0000–$1FFF
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
WD1
WD0
0
0
0
1
1
0
1
1
Watchdog Time Out
(Typical)
1.4 seconds
600 milliseconds
200 milliseconds
disabled
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. This flag can be used by the sys-
tem to determine whether a reset occurs as a result of
a watchdog time out or power failure.
The nonvolatile WPEN bit is programmed using the
WRSR instruction. This bit works in conjunction with the
WP pin to provide an in-circuit programmable ROM func-
tion (Table 2). WP is LOW and WPEN bit programmed
HIGH disables all status register write operations.
In Circuit Programmable ROM Mode
This mechanism protects the block lock and watchdog
bits from inadvertent corruption.
In the locked state (programmable ROM mode) the WP
pin is LOW and the nonvolatile bit WPEN is “1”. This
mode disables nonvolatile writes to the device’s status
register.
REV 1.1.1 3/5/01
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Characteristics subject to change without notice. 6 of 19