 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 Appendixnear Pointers
Pointers to near objects are stored using two bytes (16 bits). The bytes are stored little endian or low to high order. In the tiny memory model, near pointers contain a 16-bit memory address. In all other memory models, near pointers contain a 14-bit offset in bits 0-13 and a 2-bit DPP selector in bits 14 and 15.
A near pointer is stored in memory at a word boundary as follows:
| Address+0 | Address+1 | |
|---|---|---|
| Contents | Offset (LSB) | Offset (MSB) |
The 2-bit DPP selector allows access to the following memory types:
| DPP Selector Value | Memory Type |
|---|---|
| 0 | Unused in C166 near pointers. |
| 1 | NCONST group (objects defined with const near). |
| 2 | NDATA group (objects defined with near). |
| 3 | SDATA or SYSTEM group (objects defined with sdata, idata, or bdata). |
You may use the L166 Linker DPPUSE directive to manually configure the DPP register assignments.
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