Rainbow Electronics T89C51AC2 - Manual (Page 19)

19
T89C51AC2
Rev. B – 19-Dec-01
7. Data Memory
The T89C51AC2 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 1024 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 2 shows the internal and external data memory spaces organization.
Figure 1. Internal memory - RAM
Figure 2. 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 1024 bytes
00h
64 Kbytes
External XRAM
0000h
FFFFh
Internal ERAM
EXTRAM= 0
EXTRAM= 1
FFh or 3FFh
Internal External