Datasheet

20
AT89C51AC3
4383D–8051–02/08
Data Memory The AT89C51AC3 provides data memory access in two different spaces:
1. The internal space mapped in three separate segments:
• the lower 128 Bytes RAM segment.
• the upper 128 Bytes RAM segment.
• the expanded 2048 Bytes RAM segment (ERAM).
2. The external space.
A fourth internal segment is available but dedicated to Special Function Registers,
SFRs, (addresses 80h to FFh ) accessible by direct addressing mode.
Figure 8 shows the internal and external data memory spaces organization.
Figure 7. Internal Memory - RAM
Figure 8. Internal and External Data Memory Organization ERAM-XRAM
Upper
128 Bytes
Internal RAM
Lower
128 Bytes
Internal RAM
Special
Function
Registers
80h
80h
00h
FFh
FFh
direct addressing
addressing
7Fh
direct or indirect
indirect addressing
256 up to 2048 Bytes
00h
64K Bytes
External XRAM
0000h
FFFFh
Internal ERAM
EXTRAM = 0
EXTRAM = 1
FFh or 7FFh
Internal
External