Internal Data Memory Xram - Siemens C500 User Manual

While the SFR area and the upper internal RAM area share the same address locations (80 H -
FF H ), they must be accessed through different addressing modes. The upper internal RAM can
only be accessed through indirect addressing while the special function registers (SFRs) are
accessible only by direct addressing instructions. The SFRs which are located at addresses with
address bit 0-2 equal 0 (addresses 80 H , 88 H , 90 H , ....F0 H , FF H ) are bitaddressable SFRs.
1.2.2.2

Internal Data Memory XRAM

Some members of the C500 family microcontrollers provide an additional internal data memory
area, called the XRAM. This data memory area is logically located at the upper end of the external
data memory space (except C502), but it is integrated on the chip. Because the XRAM is used in
the same way as external data memory the same instruction types must be used for accessing the
XRAM.
Figure 1-3 shows a typical 256 byte XRAM address mapping of the C500 microcontrollers.
Figure 1-3
XRAM Memory Mapping (256 Byte)
Depending on the C500 derivative, the size of the XRAM area differs from 128 upto 3K byte.
Further, the XRAM can be enabled or disabled. If an internal XRAM area is disabled, external data
memory can be accessed in the address range of the internal XRAM.
Semiconductor Group
FFFF H
FEFF
H
External
Data
Memory
0000 H
XRAM is located at the upper end of the external data memory area.
Internal
XRAM
1-5
Fundamental Structure
C500 Family
FFFF
H
FF00 H
MCD02768
1998-04-01