X45620 Datasheet, PDF (18/20 Pages) Intersil Corporation – Dual Voltage Monitor with Integrated System Battery Switch and EEPROM

X45620
WEL: Write Enable Latch (Volatile)
The WEL bit controls the access to the memory and to
the Register during a write operation. This bit is a volatile
latch that powers up in the LOW (disabled) state. While
the WEL bit is LOW, writes to any address, including any
control registers will be ignored (no acknowledge will be
issued after the Data Byte). The WEL bit is set by writing
a “1” to the WEL bit and zeros to the other bits of the con-
trol register. Once set, WEL remains set until either it is
reset to 0 (by writing a “0” to the WEL bit and zeros to the
other bits of the control register) or until the part powers
up again. Writes to WEL bit do not cause a high voltage
write cycle, so the device is ready for the next operation
immediately after the stop condition.
BP1, BP0: Block Protect Bits (Nonvolatile)
The Block Protect Bits, BP1 and BP0, determine which
blocks of the array are write protected. A write to a pro-
tected block of memory is ignored. The block protect bits
will prevent write operations to one of four segments of
the array. The partitions are described in Table 2.
WD1, WD0: Watchdog Timer Bits (Nonvolatile)
The Watchdog Timer circuit monitors the micro-
processor activity by monitoring the SCL and SDA pins.
In normal operation, the microprocessor must
periodically restart the Watchdog Timer to prevent WDO
from going active. The watchdog timer is restarted on the
first HIGH to LOW transition on SCL after a start
command. The state of two nonvolatile control bits in the
Status Register determines the watchdog timer period.
The microprocessor can change these watchdog bits by
writing to the status register.
The Watchdog Timer oscillator stops when in battery
backup mode. It re-starts when V_CC returns.
Status Register Bit
WD1
WD0
0
0
0
1
1
0
1
1
Watchdog Time Out
(Typical)
800 milliseconds
400 milliseconds
150 milliseconds
Disabled (factory setting)
Write Protect Enable Bit—WPEN (Nonvolatile)
The Write Protect (WP) pin and the Write Protect Enable
(WPEN) bit in the Control Register control the Program-
mable Hardware Write Protect feature. Hardware Write
Protection is enabled when the WP pin is connected to
V_CC and the WPEN bit is HIGH, and disabled when WP
pin is connected to ground. When the chip is in ROM
mode, nonvolatile writes are disabled to all non-volatile
bits in the CR, including the Block Protect bits and the
WPEN bit itself, as well as to the block protected sections
in the memory array. Only the sections of the memory
array that are not block protected can be written. Note
that since the WPEN bit is write protected, it cannot be
changed back to a LOW state; so write protection is
enabled as long as the WP pin is held connected to V_CC.
PUP: Power-on Reset (Nonvolatile)
The Power-on reset time (t_PURST) bit, PUP, sets the
initial power-on reset time. There are two standard
settings.
PUP
0
1
Time
150 ms (factory settings)
800 ms
Note 1. Watchdog timer is shipped disabled.
2. The t_PURST time is set to 150ms at the factory.
Any changes to the Control Register take effect,
following either the next command (read or write) or
cycling the power to the device.
The recommended procedure for changing the
Watchdog Timer settings is to do a WREN, followed
by a write status register command. Then execute a
software loop to read the status register until an ACK
is returned (ACK polling) complete the read operation.
A valid alternative is to do a WREN, followed by a
write status register command. Then wait 10ms and
do a read status command.
Table 2. Block Protect Bits
BP1
BP0
0
0
0
1
1
0
1
1
Protected Addresses
None
6000h - 7FFFh (8K bytes)
4000h - 7FFFh (16K bytes)
0000h - 7FFFh (32K bytes)
Array Lock
None (factory setting)
Upper 1/4 (Q4)
Upper 1/2 (Q3, Q4)
Full Array (All)
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FN8250.0
July 29, 2005