AT89C51ED2-RDTIM datasheet(96/137 Pages) ATMEL

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AT89C51RD2/ED2

4235E–8051–04/04

Flash Registers and

Memory Map

The AT89C51RD2/ED2 Flash memory uses several registers for its management:

•

Hardware registers can only be accessed through the parallel programming modes

which are handled by the parallel programmer.

•

Software registers are in a special page of the Flash memory which can be

accessed through the API or with the parallel programming modes. This page,

called "Extra Flash Memory", is not in the internal Flash program memory

addressing space.

Hardware Register

The only hardware register of the AT89C51RD2/ED2 is called Hardware Security Byte

(HSB).

Table 67. Hardware Security Byte (HSB)

Boot Loader Jump Bit (BLJB)

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

•

When this bit is programmed (‘1’ value) the boot address is 0000h.

•

When this bit is unprogrammed (‘1’ value) the boot address is F800h. By default,

this bit is unprogrammed and the ISP is enabled.

Flash Memory Lock Bits

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

when programmed as shown in Table 68.

BLJB

OSC

XRAM

LB2

LB1

LB0

Bit

Number

Bit

Mnemonic

Description

7X2

X2 Mode

Programmed (‘0’ value) to force X2 mode (6 clocks per instruction) after reset.

Unprogrammed (‘1’ Value) to force X1 mode, Standard Mode, after reset

(Default).

6BLJB

Boot Loader Jump Bit

Unprogrammed (‘1’ value) to start the user’s application on next reset at address

0000h.

Programmed (‘0’ value) to start the boot loader at address F800h on next reset

(Default).

5OSC

Oscillator Bit

Programmed to allow oscillator B at startup

Unprogrammed this bit to allow oscillator A at startup (Default).

Reserved

3XRAM

XRAM config bit (only programmable by programmer tools)

Programmed to inhibit XRAM.

Unprogrammed, this bit to valid XRAM (Default).

2-0

LB2-0

User Memory Lock Bits (only programmable by programmer tools)

See Table 68

AT89C51ED2-RDTIM 数据表(PDF) 96 Page - ATMEL Corporation

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