User Space
This space is composed of a 64K Bytes ROM memory programmed during the manu-
facturing process. It contains the user’s application code.
Flash Memory
Architecture
As shown in Figure 11 the AT89C51SND2C Flash memory is composed of four spaces
detailed in the following paragraphs.
Figure 11. AT89C51SND2C Memory Architecture
Hardware Security
Extra Row
FFFFh
FFFFh
4K Bytes
Flash Memory
Boot
F000h
64K Bytes
User
Flash Memory
0000h
User Space
Boot Space
This space is composed of a 64K Bytes Flash memory organized in 512 pages of 128
Bytes. It contains the user’s application code.
This space can be read or written by both software and hardware modes.
This space is composed of a 4K Bytes Flash memory. It contains the boot loader for In-
System Programming and the routines for In Application Programming.
This space can only be read or written by hardware mode using a parallel programming
tool.
Hardware Security Space
This space is composed of one Byte: the Hardware Security Byte (HSB see Table 23)
divided in 2 separate nibbles. The MSN contains the X2 mode configuration bit and the
Boot Loader Jump Bit as detailed in Section “Boot Memory Execution”, page 19 and can
be written by software while the LSN contains the lock system level to protect the mem-
ory content against piracy as detailed in Section “Hardware Security System”, page 19
and can only be written by hardware.
Extra Row Space
This space is composed of 2 Bytes:
•
The Software Boot Vector (SBV, see Table 24).
This Byte is used by the software boot loader to build the boot address.
•
The Software Security Byte (SSB, see Table 25).
This Byte is used to lock the execution of some boot loader commands.
18
AT8xC51SND2C
4341D–MP3–04/05
ATMEL [ ATMEL ]
