X40430/X40431 – Preliminary Information
BP1, BP0: Block Protect Bits (Nonvolatile)
– Write one byte value to the Control Register that has
all the control bits set to the desired state. The Con-
trol register can be represented as qxys t01r in
binary, where xy are the WD bits, and st are the BP
bits and qr are the power up bits. This operation pro-
ceeded by a start and ended with a stop bit. Since
this is a nonvolatile write cycle it will take up to 10ms
(max.) 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 (qxys t11r) then the RWEL bit is set, but
the WD1, WD0, PUP1, PUP0, BP1 and BP0 bits
remain unchanged. Writing a second byte to the con-
trol register is not allowed. Doing so aborts the write
operation and returns a NACK.
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 eight seg-
ments of the array.
Protected Addresses
(Size)
Array Lock
None
0
0
1
1
0
1
0
1
None
180h – 1FFh (128 bytes)
Upper 1/4 (Q4)
100h – 1FFh (256 bytes) Upper 1/2 (Q3,Q4)
000h – 1FFh (512 bytes) Full Array (All)
PUP1, PUP0: Power Up Bits (Nonvolatile)
– A read operation occurring between any of the previ-
ous operations will not interrupt the register write
operation.
The Power Up bits, PUP1 and PUP0, determine the
t
time delay. The nominal power up times are
PURST
shown in the following table.
– 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.
PUP1 PUP0 Power on Reset Delay (t
)
PURST
0
0
1
1
0
1
0
1
50ms
200ms
400ms
800ms
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.
WD1, WD0: Watchdog Timer Bits (Nonvolatile)
The bits WD1 and WD0 control the period of the
Watchdog Timer.The options are shown below.
Fault Detection Register (FDR)
The Fault Detection Register provides the user the
status of what causes the system reset active. The
Manual Reset Fail, Watchdog Timer Fail and Three
Low Voltage Fail bits are volatile
WD1
WD0
Watchdog Time Out Period
1.4 seconds
0
0
1
1
0
1
0
1
200 milliseconds
25 milliseconds
disabled
7
6
5
4
3
2
1
0
LV1F LV2F LV3F WDF MRF
0
0
0
The FDR is accessed with a special preamble in the
slave byte (1011) and is located at address 0FFh. It
can only be modified by performing a byte write opera-
tion directly to the address of the register and only one
data byte is allowed for each register write operation.
Writing to the Control Registers
Changing any of the nonvolatile bits of the control and
trickle registers 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 preceded
by a start and ended with a stop).
There is no need to set the WEL or RWEL in the
control register to access this FDR.
– Write a 06H to the Control Register to set 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 proceeded by a start
and ended with a stop).
Characteristics subject to change without notice. 8 of 24
REV 1.2.3 11/28/00
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