SAB80515 Datasheet, PDF (19/270 Pages) Siemens Semiconductor Group – 8-Bit Single-Chip Microcontroller Family

Memory Organization
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Memory Organization
The SAB 80(C)515 CPU manipulates operands in the following four address spaces:
– up to 64 Kbyte of program memory
– up to 64 Kbyte of external data memory
– 256 bytes of internal data memory
– a 128-byte special function register area
4.1 Program Memory
The program memory of the SAB 80(C)515 consists of an internal and an external memory portion
(see figure 4-1). 8 Kbyte of program memory may reside on-chip (SAB 80C515/80515 only), while
the SAB 80C535/80535 has no internal ROM. The program memory can be externally expanded
up to 64 Kbyte. If the EA pin is held high, the SAB 80(C)515 executes out of the internal program
memory unless the address exceeds 1FFFH. Locations 2000H through 0FFFFH are then fetched
from the external memory. If the EA pin is held low, the SAB 80(C)515 fetches all instructions from
the external program memory. Since the SAB 80C535/80535 has no internal program memory, pin
EA must be tied low when using this device. In either case, the 16-bit program counter is the
addressing mechanism.
Locations 03H through 93H in the program memory are used by interrupt service routines.
4.2 Data Memory
The data memory address space consists of an internal and an external memory portion.
Internal Data Memory
The internal data memory address space is divided into three physically separate and distinct
blocks: the lower 128 bytes of RAM, the upper 128-byte RAM area, and the 128-byte special
function register (SFR) area (see figure 4-2). Since the latter SFR area and the upper RAM area
share the same address locations, they must be accessed through different addressing modes. The
map in figure 4-2 and the following table show the addressing modes used for the different RAM/
SFR spaces.
Semiconductor Group
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