M34C02 datasheet(8/19 Pages) STMICROELECTRONICS

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M34C02

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Setting the Protection, Using the Protection

The M34C02 has a software write-protection

function, using the Protecton Register, that allows

the bottom half of the memory area (addresses

00h to 7Fh) to be permanently write protected. The

write protection feature is activated by writing once

to the Protection Register (with the WC input held

at VSS).

The Protection Register is accessed with the

device select code set to 0110b (as shown in

Table 3), and the E2-E1-E0 bits set according to

the states being applied to the E2-E1-E0 pins. As

The sequence, as shown in Figure 7, is:

– Initial condition: a Write is in progress.

– Step 1: the master issues a START condition

followed by a Device Select Code (the first byte

of the new instruction).

– Step 2: if the memory is busy with the internal

write cycle, no Ack will be returned and the

master goes back to Step 1. If the memory has

terminated the internal write cycle, it responds

with an Ack, indicating that the memory is ready

to receive the second part of the next instruction

(the first byte of this instruction having been sent

during Step 1).

Figure 9. Read Mode Sequences

Note: 1. The seven most significant bits of the Device Select Code of a Random Read (in the 1st and 3rd bytes) must be identical.

DEV SEL *

BYTE ADDR

DEV SEL

DATA OUT 1

AI01942

DATA OUT N

CURRENT

ADDRESS

READ

DEV SEL

DATA OUT

RANDOM

ADDRESS

READ

DEV SEL *

DATA OUT

SEQUENTIAL

CURRENT

READ

DATA OUT N

DEV SEL *

BYTE ADDR

SEQUENTIAL

RANDOM

READ

DEV SEL *

DATA OUT 1

ACK

R/W

NO ACK

ACK

R/W

ACK

R/W

ACK

NO ACK

R/W

NO ACK

ACK

R/W

ACK

R/W

ACK

NO ACK

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