M34C02-W, M34C02-L, M34C02-R

Device operation

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3.6

Setting the Software Write-Protection

The M34C02-W has a hardware write-protection feature, using the Write Control (WC)

signal. This signal can be driven High or Low, and must be held constant for the whole

instruction sequence. When Write Control (WC) is held Low, the whole memory array

(addresses 00h to FFh) is write protected. When Write Control (WC) is held High, the write

protection of the memory array is dependent on whether software write-protection has been

set.

Software write-protection allows the bottom half of the memory area (addresses 00h to 7Fh)

to be permanently write protected irrespective of subsequent states of the Write Control

(WC) signal.

The write protection feature is activated by writing once to the Protection Register. The

Protection Register is accessed with the device select code set to 0110b (as shown in

Table 2), and the E2, E1 and E0 bits set according to the states being applied on the E2, E1

and E0 signals. As for any other write command, Write Control (WC) needs to be held Low.

Address and data bytes must be sent with this command, but their values are all ignored,

and are treated as Don’t Care. Once the Protection Register has been written, the write

protection of the first 128 Bytes of the memory is enabled, and it is not possible to unprotect

these 128 Bytes, even if the device is powered off and on, and regardless the state of Write

Control (WC).

When the Protection Register has been written, the M34C02-W no longer responds to the

device type identifier 0110b in either read or write mode.

Figure 7.

Result of setting the write protection

Default EEPROM memory area

state before write access

to the Protect Register

AI01936C

Standard

Array

FFh

Standard

Array

80h

7Fh

00h

Standard

Array

FFh

Write

Protected

Array

80h

7Fh

00h

State of the EEPROM memory

area after write access

to the Protect Register

Memory

Area