When R13 is specified as the base register of the RAM section, accesses to the RAM section are performed relative to the R13 register. Furthermore, if optimization of inter-module external variable accesses is enabled, the value relative to the R13 register is optimized, and the instruction size becomes smaller if the value is 8 bits or less.

[Example]

Source code before improvement

int a;

int b;

int c;

int d;

void fu{

     a=0;

     b=1;

     c=2;

     d=3;

}

Assembly-language expansion code before improvement

_func:

     MOV.L #_a,R4

     MOV.L #0000000H,[R4]

     MOV.L #_b,R4

     MOV.L #00000001H,{R4}

     MOV.L #_c,R4

     MOV.L #00000002H,[R4]

     MOV.L #_d,[R4]

     MOV.L #00000003H,[R4]

     RTS

Source code after improvement

int a;

int b;

int c;

int d;

void fu{

     a=0;

     b=1;

     c=2;

     d=3;

}

Assembly-language expansion code after improvement

_func:

     MOV.L #0000000H,_a-__RAM_TOP:16[R13]

     MOV.L #0000001H,_b-__RAM_TOP:16[R13]

     MOV.L #0000002H,_c-__RAM_TOP:16[R13]

     MOV.L #0000003H,_d-__RAM_TOP:16[R13]

     RTS