NEC 78K/0 Series DEC

72

CHAPTER 5 EXPLANATION OF INSTRUCTIONS

User's Manual U12326EJ4V0UM

Decrement

DEC Byte Data Decrement

[Instruction format] DEC dst

[Operation] dst ← dst – 1

[Operand]

Mnemonic Operand(dst)

DEC r

saddr

[Flag]

ZACCY

××

[Description]

• The destination operand (dst) contents are decremented by only one.

• If the decrement result is 0, the Z flag is set (1). In all other cases, the Z flag is cleared (0).

• If the decrement generates a carry for bit 3 out of bit 4, the AC flag is set (1). In all other cases, the AC

flag is cleared (0).

• Because this instruction is frequently used for decrement of a counter for repeated operations and an indexed

addressing offset register, the CY flag contents are not changed (to hold the CY flag contents in multiple-

byte operation).

• If dst is the B or C register or saddr, and it is not desired to change the AC and CY flag contents, the DBNZ

instruction can be used.

[Description example]

DEC FE92H; The contents at address FE92H are decremented.

Contents

Main Page IEBus is a trademark of NEC Corporation. NOTES FOR CMOS DEVICES 4 Regional Information NEC Electronics Hong Kong Ltd. Device availability Ordering information Product release schedule Page INTRODUCTION Page Page Page Page Page 1.7 Special Function Register (SFR) Area 1.8 External Memory Space 1.9 IEBusTM Register Area 14 CHAPTER 2 REGISTERS 2.1 Control Registers Page Figure 2-5. Data to Be Reset from Stack Memory 2.2 General-Purpose Registers CHAPTER 2 REGISTERS Figure 2-6. General-Purpose Register Configuration (a) Absolute names (b) Functional names 2.3 Special Function Registers (SFRs) 20 CHAPTER 3 ADDRESSING 3.1 Instruction Address Addressing Page Page Page 3.2 Operand Address Addressing Page Page Page Page Page Page Page 32 CHAPTER 4 INSTRUCTION SET 4.1 Operation Page Page CHAPTER 4 INSTRUCTION SET Note Except r = A. CHAPTER 4 INSTRUCTION SET Note Only when rp = BC, DE or HL. (2) 16-bit instructions MOVW, XCHW, ADDW, SUBW, CMPW, PUSH, POP, INCW, DECW (3) Bit manipulation instructions MOV1, AND1, OR1, XOR1, SET1, CLR1, NOT1, BT, BF, BTCLR Page 4.2 Instruction Codes 4.2.2 Instruction code list Notes 1. Only when rp = BC, DE or HL. 2. Except r = A. Page Page Page Page Page Page Page Page MOV XCH Page MOVW XCHW Page ADD ADDC SUB SUBC AND OR XOR CMP Page ADDW SUBW CMPW Page MULU DIVUW Page INC DEC INCW DECW Page ROR ROL RORC ROLC ROR4 ROL4 Page ADJBA ADJBS Page MOV1 AND1 OR1 XOR1 SET1 CLR1 NOT1 Page CALL CALLF CALLT BRK RET RETI RETB Page PUSH POP MOVW SP , src MOVW AX, SP Page BR Page BC BNC BZ BNZ BT BF BTCLR DBNZ Page SEL RBn NOP EI DI HALT STOP APPENDIX A REVISION HISTORY 124 APPENDIX B INSTRUCTION INDEX (MNEMONIC: BY FUNCTION) Page 126 APPENDIX C INSTRUCTION INDEX (MNEMONIC: IN ALPHABETICAL ORDER) Page Page Facsimile Message Thank you for your kind support. From: