X4003 Datasheet, PDF (6/18 Pages) Xicor Inc. – CPU Supervisor

X4003/X4005
The state of the control register can be read at any
time by performing a serial read operation. Only one
byte is read by each register read operation. The
X4003/X4005 resets itself after the first byte is read.
The master should supply a stop condition to be con-
sistent with the bus protocol, but a stop is not required
to end this operation.
76 5 4
0 WD1 WD0 0
3
2
10
0 RWEL WEL 0
RWEL: Register Write Enable Latch (Volatile)
The RWEL bit must be set to “1” prior to a write to the
control register.
WEL: Write Enable Latch (Volatile)
The WEL bit controls the access to the control 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 the control register 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
zeroes to the other bits of the control register. Once
set, WEL remains set until either it is reset to 0 (by writ-
ing a “0” to the WEL bit and zeroes to the other bits of
the control register) or until the part powers up again.
Writes to the WEL bit do not cause a nonvolatile write
cycle, so the device is ready for the next operation
immediately after the stop condition.
WD1, WD0: Watchdog Timer Bits
The bits WD1 and WD0 control the period of the watch-
dog timer. The options are shown below.
WD1
0
0
1
1
WD0
0
1
0
1
Watchdog Time Out Period
1.4 seconds
600 milliseconds
200 milliseconds
Disabled (factory setting)
Writing to the Control Register
Changing any of the nonvolatile bits of the control register
requires the following steps:
– Write a 02H to the control register to set the write
enable latch (WEL). This is a volatile operation, so
there is no delay after the write. (Operation pre-
ceeded by a start and ended with a stop.)
– Write a 06H to the control register to set both the
register write enable latch (RWEL) and the WEL bit.
This is also a volatile cycle. The zeros in the data
byte are required. (Operation preceeded by a start
and ended with a stop.)
– Write a value to the control register that has all the
control bits set to the desired state. This can be rep-
resented as 0xy0 0010 in binary, where xy are the
WD bits. (Operation preceeded by a start and ended
with a stop.) Since this is a nonvolatile write cycle it
will take up to 10ms to complete. The RWEL bit is
reset by this cycle and the sequence must be
repeated to change the nonvolatile bits again. If bit 2
is set to ‘1’ in this third step (0xy0 0110) then the
RWEL bit is set, but the WD1 and WD0 bits remain
unchanged. Writing a second byte to the control reg-
ister is not allowed. Doing so aborts the write opera-
tion and returns a NACK.
– A read operation occurring between any of the previ-
ous operations will not interrupt the register write
operation.
– The RWEL bit cannot be reset without writing to the
nonvolatile control bits in the control register, power
cycling the device or attempting a write to a write
protected block.
To illustrate, a sequence of writes to the device consist-
ing of [02H, 06H, 02H] will reset all of the nonvolatile
bits in the control register to 0. A sequence of [02H,
06H, 06H] will leave the nonvolatile bits unchanged
and the RWEL bit remains set.
SERIAL INTERFACE
Serial Interface Conventions
The device supports a bidirectional bus oriented proto-
col. The protocol defines any device that sends data
onto the bus as a transmitter, and the receiving device
as the receiver. The device controlling the transfer is
called the master and the device being controlled is
called the slave. The master always initiates data trans-
fers, and provides the clock for both transmit and
receive operations. Therefore, the devices in this family
operate as slaves in all applications.
Serial Clock and Data
Data states on the SDA line can change only during
SCL LOW. SDA state changes during SCL HIGH are
reserved for indicating start and stop conditions. See
Figure 5.
REV 1.1.3 4/30/02
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Characteristics subject to change without notice. 6 of 18