X24645PI datasheet(9/18 Pages) XICOR

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X24645

WRITE PROTECT REGISTER

The Write Protect Register (WPR) is located at the

highest address, 1FFFh.

Figure 11. Write Protect Register

WPR.1 = WEL

–

“Write Enable” Latch (Volatile)

0 = Write enable latch reset, writes disabled

1 = Write enable latch set, writes enabled

If WEL = “0” then “no ACK” after ﬁrst byte of input data.

WPR.2 = RWEL

–

“Register Write Enable” Latch (Volatile)

0 = Register write enable latch reset, writes dis-

abled

1 = Register write enable latch set, writes enabled

WPR.3, WPR.4 = BP0, BP1

–

Block Protect Bits (Nonvolatile)

(See Block Protect section for definition)

WPR.7 = WPEN

–

Write Protect Enable Bit (Nonvolatile)

(See Hardware Write Protect section for definition)

Writing to the Write Protect Register

The Write Protect Register is written by performing a

random write of one byte directly to address, 1FFFh. If

a page write is performed starting with any address

other than 1FFF, the byte in the array at address

1FFFh will be written instead of the Write Protect

block protect register).

The state of the Write Protect Register can be read by

performing a random read at address 1FFFh at any

time. If a sequential read starting at any other address

than 1FFFh is performed, the contents of the byte in

the array at 1FFFh is read out instead of the Write

Protect Register.

WPEN

BP1

BP0

RWEL

WEL

2783 ILL F15.1

WPR (ADDR = 1FFFh)

WEL and RWEL are volatile latches that power-up in

the LOW (disabled) state. A write to any address other

than 1FFFh, where the Write Protect Register is

located, will be ignored (no ack) until the WEL bit is set

HIGH. The WEL bit is set by writing 0000001x to

address 1FFFh. Once set, WEL remains HIGH until

either reset (by writing 00000000 to 1FFFh) or until the

part powers-up again. The RWEL bit controls writes to

the block protect bits. RWEL is set by ﬁrst setting WEL

to “1” and then writing 0000011x to address 1FFFh.

RWEL must be set in order to change the block protect

bits, BP0 and BP1, or the WPEN bit. RWEL is reset

when the block protect or WPEN bits are changed, or

when the part powers-up again.

Programming the BP or WPEN Bits

A three step sequence is required to change the

nonvolatile Block Protect or Write Protect Enable:

1) Set WEL = 1 (write 00000010 to address 1FFFh,

volatile write cycle)

(Start)

2) Set RWEL = 1 (write 00000110 to address 1FFFh,

volatile write cycle)

(Start)

3) Set BP1, BP0, and/or WPEN bits (Write w00yz010

to address 1FFFh)

w = WPEN, y = BP1, Z = BP0,

(Stop)

Step 3 is a nonvolatile write cycle, requiring 10ms to

complete. RWEL is reset to “0” by this write cycle,

requiring another write cycle to set RWEL again before

the block protect bits can be changed. RWEL must be

“0” in step 3; if w00yz110 is written to address 1FFFh,

RWEL is set but WPEN, BP1 and BP0 are not

changed (the device remains at step 2).

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