AT89C51RC-33AC ATMEL Corporation, AT89C51RC-33AC Datasheet - Page 9

• Manufacturer Part Number: AT89C51RC-33AC
• Description: 8-bit Microcontroller with 32K Bytes Flash
• Manufacturer: ATMEL Corporation

Table 3b. AUXR1: Auxiliary Register 1
Memory Organization
Program Memory
Data Memory
1920B–MICRO–11/02
AUXR1
–
DPS
Reserved for future expansion
Data Pointer Register Select
DPS
0
1
Address = A2H
Not Bit Addressable
Bit
Selects DPTR Registers DP0L, DP0H
Selects DPTR Registers DP1L, DP1H
–
7
MCS-51 devices have a separate address space for Program and Data Memory. Up to
64K bytes each of external Program and Data Memory can be addressed.
If the EA pin is connected to GND, all program fetches are directed to external memory.
On the AT89C51RC, if EA is connected to V
through 7FFFH are directed to internal memory and fetches to addresses 8000H
through FFFFH are to external memory.
The AT89C51RC has internal data memory that is mapped into four separate segments:
the lower 128 bytes of RAM, upper 128 bytes of RAM, 128 bytes special function regis-
ter (SFR) and 256 bytes expanded RAM (ERAM).
The four segments are:
1. The Lower 128 bytes of RAM (addresses 00H to 7FH) are directly and indirectly
2. The Upper 128 bytes of RAM (addresses 80H to FFH) are indirectly addressable
3. The Special Function Registers, SFRs, (addresses 80H to FFH) are directly
4. The 256-byte expanded RAM (ERAM, 00H-FFH) is indirectly accessed by MOVX
The Lower 128 bytes can be accessed by either direct or indirect addressing. The Upper
128 bytes can be accessed by indirect addressing only. The Upper 128 bytes occupy
the same address space as the SFR. This means they have the same address, but are
physically separate from the SFR space.
When an instruction accesses an internal location above address 7FH, the CPU knows
whether the access is to the upper 128 bytes of data RAM or to SFR space by the
addressing mode used in the instruction. Instructions that use direct addressing access
SFR space. For example:
MOV 0A0H, # data
addressable.
only.
addressable only.
instructions, and with the EXTRAM bit cleared.
–
6
–
5
–
4
–
3
CC
, program fetches to addresses 0000H
–
2
Reset Value = XXXXXXX0B
–
1
AT89C51RC
DPS
0
9