Relocatable Data

The limited RAM size of the RS08 requires careful data allocation. Access global read/write data using tiny, short, direct, or paged addressing. Access global read-only data using paged or far addressing. RS08 non-static local data must be allocated into an OVERLAP section. The compiler does this allocation automatically, using the same address range as is used for direct addressing (0x00 to 0xBF).

• Use tiny addressing (__TINY_SEG) for frequently accessed global variables when the operand can be encoded on four bits. The address range for these variables is 0x00 - 0x0F.
• Use short addressing (__SHORT_SEG) to access IO registers in the lower RS08 register bank, when the operand can be encoded on five bits. The address range for these variables is 0x00 - 0x1F.
• Use direct (8-bit) addressing (DEFAULT) to access global variables when the operand is greater than four or five bits. The address range for these variables is 0x00 to 0xBF.
• Use paged addressing (__PAGED_SEG) to access IO registers in the upper RS08 register bank. The address range for these variables is 0x100 to 0x3FF.
• Use paged addressing (__PAGED_SEG) to access global read-only (constant) data. Objects allocated in PAGED sections must not cross page boundaries. The address range for these constants is 0x00 to 0x3FFF.
• Use far addressing (__FAR_SEG) to access large constant data. Allocate far sections to more than one page. The address range for these constants is 0x00 to 0x3FFF.

See the following listing for examples using the different addressing modes.

/* in a header file */ #pragma DATA_SEG __TINY_SEG MyTinySection 
char status; 
#pragma DATA_SEG __ SHORT_SEG MyShortSection 
unsigned char IOReg; 
#pragma DATA_SEG DEFAULT 
char temp; 
#pragma DATA_SEG __ PAGED_SEG MyShortSection 
unsigned char IOReg; 
unsigned char *__paged io_ptr = &IOREG; 
#pragma DATA_SEG __ PAGED_SEG MyPagedSection 
const char table[10]; 
unsigned char *__paged tblptr = table; 
#pragma DATA_SEG __ FAR_SEG MyFarSection 
const char table[1000]; 
unsigned char *__far tblptr = table; 

The segment must be placed on the direct page in the PRM file.

LINK test.abs NAMES test.o startup.o ansi.lib END 
SECTIONS 
    Z_RAM  = READ_WRITE  0x0080 TO 0x00FF; 
    MY_RAM = READ_WRITE  0x0100 TO 0x01FF; 
    MY_ROM = READ_ONLY   0xF000 TO 0xFEFF; 
PLACEMENT 
    DEFAULT_ROM                    INTO MY_ROM; 
    DEFAULT_RAM                    INTO MY_RAM; 
    _ZEROPAGE, myShortSegment       INTO Z_RAM; 
END 
VECTOR 0 _Startup /* set reset vector on _Startup */ 

• Using -Ostk