AT89C51IC2 Datasheet, PDF (108/147 Pages) ATMEL Corporation – 8-bit Flash Microcontroller with 2-wire Interface

Flash Registers and
Memory Map
Hardware Register
Flash Memory Lock Bits
The AT89C51IC2 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.
The only hardware register of the AT89C51IC2 is called Hardware Security Byte (HSB).
Table 84. Hardware Security Byte (HSB)
7
6
5
X2
BLJB
OSC
4
3
2
1
0
-
XRAM
LB2
LB1
LB0
Bit
Bit
Number Mnemonic Description
X2 Mode
Programmed (‘0’ value) to force X2 mode (6 clocks per instruction) after reset.
7
X2
Unprogrammed (‘1’ Value) to force X1 mode, Standard Mode, after reset
(Default).
Boot Loader Jump Bit
Unprogrammed (‘1’ value) to start the user’s application on next reset at address
6
BLJB 0000h.
Programmed (‘0’ value) to start the boot loader at address F800h on next reset
(Default).
Oscillator Bit
5
OSC Programmed to allow oscillator B at startup
Unprogrammed this bit to allow oscillator A at startup ( Default).
4
-
Reserved
XRAM config bit (only programmable by programmer tools)
3
XRAM Programmed to inhibit XRAM
Unprogrammed, this bit to valid XRAM (Default)
User Memory Lock Bits (only programmable by programmer tools)
2-0
LB2-0
See Table 85
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.
The three lock bits provide different levels of protection for the on-chip code and data,
when programmed as shown in Table 85.
108 AT89C51IC2
4301C–8051–06/06