Accessing Data Objects Examples

The tables below show appropriate ways to access a global integer and a global pointer variable. The first two columns of each table list states of two checkboxes, Large Data Model and Globals live in lower memory. Both checkboxes are in the M56800E Processor settings panel; the first enables the second.

The following table lists ways to access a global integer stored at address X:0x1234.

int g1;

Table 1. Accessing Global Integer
Large Data Model checkbox	Globals Live in Lower Memory Checkbox	Instruction	Comments
Clear	Clear	move.w X:0x1234,y0	Default values
Checked	Clear	move.w X:0x001234,y0
Clear	Checked	Combination not allowed
Checked	Checked	move.w X:0x1234,y0	Global accesses use 16-bit addressing

The following table lists ways to load a global pointer variable, at X:0x4567, into an address register.

 int * gp1;

Table 2. Loading Global Pointer Variable
Large Data Model checkbox	Globals Live in Lower Memory Checkbox	Instruction	Comments
Clear	Clear	move.w X:0x4567,r0	Default 16-bit addressing, 16-bit pointer value
Checked	Clear	move.l X:0x004567,r0	24-bit addressing, pointer value is 24-bit
Clear	Checked	Combination not allowed
Checked	Checked	move.l X:0x4567,r0	16-bit addressing, pointer value is 24-bit