M34C02-RMM1 查看數據表（PDF） - STMicroelectronics

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M34C02-RMM1

2 Kbit Serial I²C Bus EEPROM For DIMM Serial Presence Detect

STMicroelectronics 

M34C02

Figure 6. Setting the Write Protection Register (WC = 0)

BUS ACTIVITY

MASTER

SDA LINE

BUS ACTIVITY

CONTROL

BYTE

WORD

ADDRESS

DATA

ACK

ACK

ACK

VALUE

VALUE

(DON'T CARE) (DON'T CARE)

AI01935B

Setting the Software Write-Protection

The M34C02 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 no longer responds to the device type

identifier 0110b in either read or write mode.

Figure 7. Result of Setting the Write Protection

Memory

Area

FFh

Standard

Array

80h

7Fh

Standard

Array

00h

Default EEPROM memory area

state before write access

to the Protect Register

FFh

Standard

Array

80h

7Fh

Write

Protected

Array

00h

State of the EEPROM memory

area after write access

to the Protect Register

AI01936C

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