Файл: Microcontroller Programming. Thi Micro Chip PIC (Julio Sanchez, 2007).pdf

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634

Appendix C

COMF

Complement f

Syntax:

[ label ] COMF

f,d

Operands:

f in range 0 to 127

d is 0 or 1

Operation:

(f) -> destination

Status Affected:

Z

Description:

The contents of register 'f' are 1’s

complemented. If 'd' is 0 the result is stored in

w. If 'd' is 1 the result is stored back in register

'f'.

Words:

1

Cycles:

1

Example 1:

comf

reg1,0

Before Instruction:

reg1

=

0x13

After Instruction:

reg1

=

0x13

w = 0xEC

Example 2:

comf

INDF,1

Before Instruction:

FSR = 0xc2

[FSR]= 0xAA

After Instruction:

FSR = 0xc2

[FSR] = 0x55

Example 3:

comf

reg1,1

Before Instruction:

reg1= 0xff

After Instruction:

reg1 = 0x00

Mid-range Instruction Set

635

DECF

Decrement f

Syntax:

[ label ] DECF f,d

Operands:

f in range 0 to 127

d is either 0 or 1

Operation:

(f) - 1 -> destination

Status Affected:

Z

Description:

Decrement register 'f'. If 'd' is 0 the result is

stored in the w register. If 'd' is 1 the

result is stored back in register 'f'.

Words:

1

Cycles:

1

Example 1:

decf

count,1

Before Instruction:

count = 0x01

Z = 0

After Instruction:

count = 0x00

Z = 1

Example 2:

decf

INDF,1

Before Instruction:

FSR = 0xc2

[FSR] = 0x01

Z = 0

After Instruction:

FSR = 0xc2

[FSR] = 0x00

Z = 1

Example 3:

decf

count,0

Before Instruction:

count = 0x10

w = x

Z = 0

After Instruction:

count = 0x10

w = 0x0f

636

Appendix C

DECFSZ

Decrement f, Skip if 0

Syntax:

[ label ] DECFSZ f,d

Operands:

f in the range 0 to 127

d is either 0 or 1

Operation:

(f) - 1 -> destination; skip if result = 0

Status Affected:

None

Description:

The contents of register 'f' are

decremented. If 'd' is 0 the result is placed

in the w register. If 'd' is 1 the result is

placed back in register 'f'.

If the result is 0, then the next instruction

(fetched during the current instruction

execution) is discarded and a NOP is

executed instead, making this a 2 cycle

instruction.

Words:

1

Cycles:

1(2)

Example

here:

decfsz

count,1

goto

here

Case 1:

Before Instruction:

PC = $

count = 0x01

After Instruction:

count = 0x00

PC = $ + 2 (goto skipped)

Case 2:

Before Instruction:

PC = $

count = 0x04

After Instruction:

count = 0x03

PC = $ + 1 (goto executed)

Mid-range Instruction Set

637

GOTO

Unconditional Branch

Syntax:

[ label ] GOTO k

Operands:

0 £ k £ 2047

Operation:

k -> PC<10:0>

PCLATH<4:3> ->PC<12:11>

Status Affected:

None

Description:

GOTO is an unconditional branch. The eleven

bit immediate value is loaded into PC bits

<10:0>. The upper bits of PC are loaded from

PCLATH<4:3>.

GOTO is a two cycle instruction.

Words:

1

Cycles:

2

Example

goto

There

After Instruction:

PC = address of There

638 Appendix C

INCF

Increment f

Syntax:

[ label ] INCF f,d

Operands:

f in range 0 to 127

d is either 0 or 1

Operation:

(f) + 1 -> destination

Status Affected:

Z

Description:

The contents of register 'f' are incremented. If

'd' is 0 the result is placed in the w register. If 'd'

is 1 the result is placed back in register 'f'.

Words:

1

Cycles:

1

Example 1

incf

count,1

Before Instruction:

count = 0xff

Z = 0

After Instruction:

count = 0x00

Z = 1

Example 2

incf

INDF,1

Before Instruction:

FSR = 0xC2

[FSR] = 0xff

Z = 0

After Instruction:

FSR = 0xc2

[FSR] = 0x00

Z = 1

Example 3

incf

count,0

Before Instruction:

count = 0x10

w = x

Z = 0

After Instruction:

count = 0x10

w = 0x11

Z = 0

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