Ibm uPD78082 Manual do Utilizador descarregar pdf (Página 63)

CHAPTER 3 CPU ARCHITECTURE

15 0

876

15 0

jdisp8

When S = 0, all bits of α are 0.

When S = 1, all bits of α are 1.

PC indicates the start address

of the instruction

after the BR instruction.

...

3.3 Instruction Address Addressing

An instruction address is determined by program counter (PC) contents. The contents of PC 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 instructions, refer to 78K/0 USER'S MANUAL:

Instruction (IEU-1372).

3.3.1 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 the relative addressing modes, execution branches in a relative range of –128 to +127 from the first address

of the next instruction.

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

[Illustration]

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Ibm uPD78082 Manual do Utilizador Página 63