GMS90C31 datasheet(53/59 Pages) HYNIX

53 / 59 page

GMS90 Series

Oct. 2000 Ver 3.1a

Program Memory Lock Bits

The two-level Program Lock system consists of 2

Lock bits and a 32-byte (64-byte for GMS97X54/

56/58) Encryption Array which are used to protect

the program memory against software piracy.

Encryption Array:

Within the EPROM array are 32 bytes (64 bytes

for GMS97X54/56/58) of Encryption Array that

are initially unprogrammed (all 1s). Every time

that a byte is addressed during a verify, address

lines are used to select a byte of the Encryption array. This byte is then exclusive-NORed (XNOR) with the code

byte, creating an Encrypted Verify byte.

The algorithm, with the array in the unprogrammed state (all 1s), will return the code in its original, unmodified

form, It is recommended that whenever the Encryption Array is used, at least one of the Lock Bits be pro-

grammed as well.

Program / Verify algorithms

Any algorithm in agreement with the conditions listed in Table 11, and which satisfies the timing specifications

is suitable.

Notes:

1. “0” = Valid low for that pin, "1" = valid high for that pin.

2. VPP =12.75V ± 0.25V

3. VCC =5V ± 10% during programming and verification.

4. ALE/PROG receives 25 (10 for GMS97X54/56/58) programming pulses while VPP is held at 12.75V.

Each programming pulse is low for 100us (

± 10us) and high for a minimum of 10µs.

Table 11. EPROM programming modes

MODE

RST

PSEN

ALE/

PROG

EA/

VPP

P2.7

P2.6

P3.7

P3.6

Read Signature

10110

000

Program Code Data

100

VPP

011

Verify Code Data

10110

011

Program encryption table

100

VPP

010

Program security bit 1

100

VPP

111

Program security bit 2

100

VPP

100

Lock Bit Protection Modes

U: unprogrammed, P: programmed

Mode

LB1

LB2

Protection Type

No program lock features

Further programming of the

EPROM is disabled

Same as mode2, alsoverify is

disabled

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