FM21LD16 - 128Kx16 FRAM

Rev. 3.0

Oct. 2012

Page 6 of 15

Normal Memory

Operation

Read 12555h?

Read

1DAAAh?

Any other

operation

Read 01333h?

Read

0ECCCh?

Read 000FFh?

Read 1FF00?

Hold Data Byte

(FM21LD16)

Write 0ECCC?

Data

Complement?

y

n

n

n

n

n

y

y

y

y

y

n

y

Write 1DAAA?

y

Write 0FF00?

y

n

Enter new write

protect settings

n

Read 1AAAA?

Write 0ECCC?

y

Drive write protect

data out

Read 00000?

n

y

n

Change Write Protect

Settings

Read Write Protect

Settings

Sequence Detector

Read 00000?

Figure 2. Write-Protect State Machine

For example, the following sequence write-protects addresses from 0C000h to 13FFFh (sectors 3 & 4):

Address

Data

Read

12555h

-

Read

1DAAAh

-

Read

01333h

-

Read

0ECCCh

-

Read

000FFh

-

Read

1FF00h

-

Write 1DAAAh

18h

; bits 3 & 4 = 1

Write 0ECCCh

E7h

; complement of 18h

Write 0FF00h

-

; Data is don’t care

Read

00000h

-

; return to Normal Operation