Datasheet

33
A/T89C51AC2
4127H–8051–02/08
Program/Code
Memory
The A/T89C51AC2 implement 32 KB of on-chip program/code memory. Figure 17
shows the partitioning of internal and external program/code memory spaces depending
on the product.
The Flash memory increases EPROM and ROM functionality by in-circuit electrical era-
sure and programming. Thanks to the internal charge pump, the high voltage needed for
programming or erasing Flash cells is generated on-chip using the standard VDD volt-
age. Thus, the Flash Memory can be programmed using only one voltage and allows In-
System-Programming commonly known as ISP. Hardware programming mode is also
available using specific programming tool.
Figure 17. Program/Code Memory Organization
Notes: 1. If the program executes exclusively from on-chip code memory (not from external
memory), beware of executing code from the upper byte of on-chip memory (7FFFh)
and thereby disrupt I/O Ports 0 and 2 due to external prefetch. Fetching code con-
stant from this location does not affect Ports 0 and 2.
2. Default factory programmed parts come with maximum hardware protection. Execu-
tion from external memory is not possible unless the Hardware Security Byte is
reprogrammed. See Table 26.
0000h
32 KB
7FFFh
internal
0000h
7FFFh
FFFFh
8000h
Flash
32 KB
external
memory
32 KB
external
memory
EA = 0
EA = 1