780964 datasheet(20/129 Pages) NEC

20 / 129 page

User's Manual U12326EJ4V0UM

CHAPTER 3 ADDRESSING

3.1 Instruction Address Addressing

An instruction address is determined by program counter (PC) contents. The PC contents are normally

incremented (+1 for each byte) automatically according to the number of bytes of an instruction to be fetched each

time another instruction is executed. When a branch instruction is executed, the branch destination information

is set to the PC and branched by the following addressing (for details of each instruction, refer to CHAPTER 5

EXPLANATION OF INSTRUCTIONS).

3.1.1 Relative addressing

[Function]

The value obtained by adding 8-bit immediate data (displacement value: jdisp8) of an instruction code to

the start address of the following instruction is transferred to the program counter (PC) and branched. The

displacement value is treated as signed two’s complement data (–128 to +127) and bit 7 becomes a sign

bit. In other words, in relative addressing, the value is relatively transferred to the range between –128 and

+127 from the start address of the following instruction.

This function is carried out when the “BR $addr16” instruction or a conditional branch instruction is executed.

[Illustration]

jdisp8

When S = 0,

α indicates all bits "0".

When S = 1,

α indicates all bits "1".

... PC is the start address of

the next instruction of

a BR instruction.

780964 数据表(PDF) 20 Page - NEC