IS23SC4428 Просмотр технического описания (PDF) - Integrated Silicon Solution

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IS23SC4428

1-KBYTE EEPROM WITH WRITE PROTECT FUNCTION AND PROGRAMMABLE SECURITY CODE (PSC)

Integrated Silicon Solution 

IS23SC4418

IS23SC4428

ISSI ®

IS23SC4428 SECURITY FEATURES

Overview

Without entering Programmable Security Code (PSC), only

memory read access is possible. However, the content of the

PSC addresses (1022 and 1023) cannot be read out. If

reading PSC is attempted, 00H will be output. The PSC

verification procedure must be performed in the following

sequence:

1. Write one to not-written Error Counter bit, address 1021

2. Enter first PSC byte, address 1022

3. Enter second PSC byte, address 1023

4. After successful PSC verification, the Error Counter

should be erased to reactivate the 8 PSC entry attempts.

If the PSC entry is incorrect, go back to step 1. If all the

Error Counter bits have been written, any further PSC

entry will be blocked and the memory can never be

changed again.

Writing Error Counter

The number of erased bits (logic 1) in Error Counter determines

the number of possible attempts (maximum of eight). Before

PSC entry, only writing of error counter is possible. After PSC

is successfully verified, the counter can now be erased.

Before disconnecting the supply voltage Vcc, the counter

should be erased in order to reactivate the eight attempts.

(See Figure 10.)

Entry of PSC

The least significant PSC byte beginning with the least

significant bit must be entered first and then the most significant

(see Table 1). If both PSC byte 1's and byte 2's comparisons

prove correct, the memory erase/write access will be enabled

and PSC may be changed as wished, except the

corresponding protect bits are 0 (enabled). (See Figure 11.)

Condition when supplied

IS23SC4428 is supplied by the manufacturer with a 2-byte

PSC (transport security code) which is determined in

cooperation with the customer.

Command

Entry

Writing Error Counter

RST

0

CLK

23 0 1 2

E/W

(internal

signal)

I/O

S0 S1 … D6 D7

Write

Figure 10. Writing Error Counter

99

102

Integrated Silicon Solution, Inc. — 1-800-379-4774

9

REV. A

11/01/01

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