X4643/5 – Preliminary Information
Writing to the Control Register
Changing any of the nonvolatile bits of the control reg-
ister 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
0xys t01r
in binary, where
xy
are the WD
bits, and
rst
are the BP bits. (Operation preceeded
by a start and ended with a stop). Since this is a non-
volatile write cycle it will take up to 10ms to com-
plete. The RWEL bit is reset by this cycle and the
sequence must be repeated to change the nonvola-
tile bits again. If bit 2 is set to ‘1’ in this third step
(0xys
t11r)
then the RWEL bit is set, but the WD1,
WD0, BP2, BP1 and BP0 bits remain unchanged.
Writing a second byte to the control register is not
allowed. Doing so aborts the write operation and
returns a NACK.
– A read operation occurring between any of the previ-
ous operations will not interrupt the register write
operation.
Figure 5. Valid Data Changes on the SDA Bus
– 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
transfers, 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.
SCL
SDA
Data Stable
Data Change
Data Stable
REV 1.26 4/30/02
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Characteristics subject to change without notice.
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