AT83C51SND1C_03 ATMEL [ATMEL Corporation], AT83C51SND1C_03 Datasheet - Page 23

• Manufacturer Part Number: AT83C51SND1C_03
• Description: Single-Chip Flash Microcontroller with MP3 Decoder and Human Interface
• Manufacturer: ATMEL [ATMEL Corporation]

Data Memory
Figure 15. Internal and External Data Memory Organization
Internal Space
Lower 128 Bytes RAM
4109E–8051–06/03
7FFh
00h
Internal ERAM
EXTRAM = 0
2K Bytes
The AT8xC51SND1C provides data memory access in 2 different spaces:
1. The internal space mapped in three separate segments:
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. For information
on this segment, refer to the Section “Special Function Registers”, page 30.
Figure 15 shows the internal and external data memory spaces organization.
The lower 128 Bytes of RAM (see Figure 16) are accessible from address 00h to 7Fh
using direct or indirect addressing modes. The lowest 32 Bytes are grouped into 4
banks of 8 registers (R0 to R7). 2 bits RS0 and RS1 in PSW register (see Table 28)
select which bank is in use according to Table 25. This allows more efficient use of code
space, since register instructions are shorter than instructions that use direct address-
ing, and can be used for context switching in interrupt service routines.
Table 25. Register Bank Selection
The next 16 Bytes above the register banks form a block of bit-addressable memory
space. The C51 instruction set includes a wide selection of single-bit instructions, and
the 128 bits in this area can be directly addressed by these instructions. The bit
addresses in this area are 00h to 7Fh.
FFh
7Fh
80h
00h
–
–
–
Indirect Addressing
RS1
Direct or Indirect
The lower 128 Bytes RAM segment
The upper 128 Bytes RAM segment
The expanded 2048 Bytes RAM segment
0
0
1
1
Internal RAM
Internal RAM
Addressing
128 Bytes
128 Bytes
Upper
Lower
FFh
80h
RS0
0
1
0
1
Direct Addressing
Registers
Function
Special
Description
Register bank 0 from 00h to 07h
Register bank 1 from 08h to 0Fh
Register bank 2 from 10h to 17h
Register bank 3 from 18h to 1Fh
FFFFh
0800h
0000h
AT8xC51SND1C
External XRAM
EXTRAM = 1
64K Bytes
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