DECA

DECA

Decrement a Register (AGU)

Operation

Assembler Syntax

Rx – 1 → Rx

DECA Rx

DECA

Description

DECA Rx

Subtracts one from an AGU register (Rx). SP cannot be used as a destination of this instruction.

Note: The assembler maps this instruction to SUBA #u5,Rx; where #u5 = 1.

Status and Conditions that Affect Instruction

Register Address

Bit Name

Description

MCTL[31:0]

AM3–AM0

Address modification bits when updating R0–R7. Otherwise, the

 

 

instruction is not affected by MCTL.

Status and Conditions Changed by Instruction

None.

Example

deca r0

Register/Memory Address

MCTL

R0

Before

$0000 0000

$074F 312A

After

$074F 3129

Instruction Formats and Opcodes

Instruction

Words

Cycles

Type

DECA Rx

1

1

2

Opcode

158 70

1 1 1 0 R R R R 0 1 1 i i i i i

Instruction Fields

Rx

RRRR

 

AGU Source/Destination Register

 

 

 

0000

N0

0100

1000

R0

1100

R4

 

 

 

 

 

 

 

 

 

 

0001

N1

0101

1001

R1

1101

R5

 

 

 

 

 

 

 

 

 

 

0010

N2

0110

1010

R2

1110

R6

 

 

 

 

 

 

 

 

 

 

0011

N3

0111

SP

1011

R3

1111

R7

 

 

 

 

 

 

 

 

Note:

This instruction

can specify R8-R15 as operands by using a high register prefix.

 

SC140 DSP Core Reference Manual

A-139

Page 453
Image 453
Freescale Semiconductor SC140 specifications Decrement a Register AGU, Deca r0, Rx 1 → Rx, Deca Rx