XC886_1 Datasheet, PDF (30/144 Pages) Infineon Technologies AG – 8-Bit Single-Chip Microcontroller

XC886/888CLM
Functional Description
3.2.2 Special Function Register
The Special Function Registers (SFRs) occupy direct internal data memory space in the
range 80_H to FF_H. All registers, except the program counter, reside in the SFR area. The
SFRs include pointers and registers that provide an interface between the CPU and the
on-chip peripherals. As the 128-SFR range is less than the total number of registers
required, address extension mechanisms are required to increase the number of
addressable SFRs. The address extension mechanisms include:
• Mapping
• Paging
3.2.2.1 Address Extension by Mapping
Address extension is performed at the system level by mapping. The SFR area is
extended into two portions: the standard (non-mapped) SFR area and the mapped SFR
area. Each portion supports the same address range 80_H to FF_H, bringing the number of
addressable SFRs to 256. The extended address range is not directly controlled by the
CPU instruction itself, but is derived from bit RMAP in the system control register
SYSCON0 at address 8F_H. To access SFRs in the mapped area, bit RMAP in SFR
SYSCON0 must be set. Alternatively, the SFRs in the standard area can be accessed
by clearing bit RMAP. The SFR area can be selected as shown in Figure 8.
As long as bit RMAP is set, the mapped SFR area can be accessed. This bit is not
cleared automatically by hardware. Thus, before standard/mapped registers are
accessed, bit RMAP must be cleared/set, respectively, by software.
Data Sheet
23
V0.9, 2006-12