Zilog Z08470 Manual do Utilizador descarregar pdf (Página 295)

UM008007-0715 Z80 Instruction Description

Z80 CPU

User Manual

283

RET cc

Operation

If cc true: PCL ← (sp), pCH ← (sp+1)

Op Code

RET

Operand

Description

If condition cc is true, the byte at the memory location specified by the contents of the

Stack Pointer (SP) Register pair is moved to the low-order eight bits of the Program Coun-

ter (PC). The SP is incremented and the byte at the memory location specified by the new

contents of the SP are moved to the high-order eight bits of the PC. The SP is incremented

again. The next op code following this instruction is fetched from the memory location

specified by the PC. This instruction is normally used to return to the main line program at

the completion of a routine entered by a CALL instruction. If condition cc is false, the PC

is simply incremented as usual, and the program continues with the next sequential

instruction. Condition cc is programmed as one of eight status that correspond to condition

bits in the Flag Register (Register F). These eight status are defined in the following table,

which also specifies the corresponding cc bit fields in the assembled object code.

cc Condition

Relevant

Flag

000 Non-Zero (NZ) Z

001 Zero (Z) Z

010 Non Carry (NC) C

011 Carry (C) C

100 Parity Odd (PO) P/V

101 Parity Even (PE) P/V

110 Sign Positive (P) S

111 Sign Negative (M) S

11 000

1 2 ... 290 291 292 293 294 295 296 297 298 299 300 ... 325 326

Sem comentários

Zilog Z08470 Manual do Utilizador Página 295