 C166 User's Guide | |
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C166 User's Guide
C166 Introduction Compiling Programs Language Extensions Preprocessor Advanced Programming Sections, Classes, and Groups
Special Sections Locating Sections Customization Files Startup Code STARTUP.A66 START167.A66 Basic I/O Memory Allocation TRAPS.C Optimizer Optimizer Options General Optimizations 80C166-Specific Optimizations Global Register Coloring DPP Registers Stacks System Stack User Stack Stack Sizes System Stack Size User Stack Size XBUS Memory and Peripherals On-chip XRAM XBUS Peripherals Interfacing C to Assembler Function Parameters Function Return Values Using the SRC Directive Register Usage Example Routines TINY Model SMALL Model COMPACT Model MEDIUM Model LARGE Model Data Storage Formats Bit Variables 1-byte Scalars 2-byte Scalars 4-byte Scalars float Scalars float Errors double Scalars double Errors near Pointers far Pointers huge Pointers xhuge Pointers Absolute Memory Access Absolute Access Macros Linker Location Controls Debugging Error Messages Library Reference AppendixDPP Registers
DPP Registers are assigned different values depending on the mode of the MCU.
- In the NON-SEGMENTED mode of the XC16x, C16x, and ST10, the C166 Compiler assigns the values 0-3 to DPP0-DPP3 respectively. NON-SEGMENTED mode is used for the TINY memory model.
- In the SEGMENTED mode of the XC16x, C16x, and ST10, the C166 Compiler allocates the DPP1-DPP3 registers to allow 16-bit (near) memory areas. SEGMENTED mode is used for the SMALL, COMPACT, MEDIUM, and LARGE memory models.
The following table shows how DPP registers are used in SEGMENTED mode:
| Register | Description |
|---|---|
| DPP0 | Used to access far, huge, and xhuge objects when generating code for C166-compatible devices. |
| DPP1 | Used to access the NCONST group which includes variables defined with const near. |
| DPP2 | Used to access the NDATA group which includes variables defined with near. |
| DPP3 | Used to access the SDATA or SYSTEM group which includes variables defined with sdata, idata or bdata. |
You may use the DPPUSE L166 Linker directive to reassign how DPP registers are used.
Note
- The DPP3 register is used when generating C166-compatible code to speed up copy and compare functions that access two far or huge objects.
- The MOD167 C166 Compiler directive prevents the compiler and run-time library from changing the DPP register contents.
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