T89C51RD2-3CWC-L datasheet(52/86 Pages) ATMEL

52 / 86 page

Rev. F - 15 February, 2001

T89C51RD2

8.4.2.1. Boot Loader Lock Bit (BLLB)

One bit of the HSB is used to secure by hardware the internal boot loader sector against software reprogramming.

When the BLLB is cleared, any attempt to write in the boot loader segment (Address FC00h to FFFFh) will have

no effect. This protection applies for software writing only.

Boot Loader Jump Bit (BLJB)

One bit of the HSB, the BLJB bit, is used to force the boot address:

• When this bit is set the boot address is 0000h.

• When this bit is reset the boot address is FC03h. By default, this bit is cleared and the ISP is enabled.

8.4.2.2. FLASH memory lock bits

The three lock bits provide different levels of protection for the on-chip code and data, when programmed according

to Table 29.

Table 27. Hardware Security Byte (HSB)

BLJB

BLLB

LB2

LB1

LB0

Bit

Number

Bit

Mnemonic

Description

Safe Bit

This bit must be cleared to secure the content of the HSB. Only security level can be increased.

BLJB

Boot loader Jump Bit

Set to force hardware boot address at 0000h. (unless previously force by hardware conditions as

described in the chapter 9.6).

Clear to force hardware boot address at FC03h (default).

BLLB

Boot loader Lock Bit

Set to allow programming and writing of the boot loader segment.

Clear to forbid software programming and writing of the boot loader segment (default). This protection protect

only ISP or IAP access; protection through parallel access is done globally by the lock bits LB2-0.

Reserved

Do not clear this bit.

Reserved

Do not clear this bit.

2-0

LB2-0

User Memory Lock Bits

See Table 29

T89C51RD2-3CWC-L Datasheet(PDF) 52 Page - ATMEL Corporation

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