XC888LM datasheet(30/144 Pages) INFINEON

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XC886/888CLM

Functional Description

Data Sheet

V0.9, 2006-12

3.2.2

Special Function Register

The Special Function Registers (SFRs) occupy direct internal data memory space in the

range 80

H to FFH. 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 FFH, 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.

XC888LM Datasheet(PDF) 30 Page - Infineon Technologies AG