PIC18F242 datasheet(233/332 Pages) MICROCHIP

233 / 332 page

DS39564C-page 231

PIC18FXX2

DECFSZ

Decrement f, skip if 0

Syntax:

[

label ] DECFSZ f [,d [,a]]

Operands:

≤ f ≤ 255

∈ [0,1]

Operation:

(f) – 1

→ dest,

skip if result = 0

Status Affected:

None

Encoding:

0010

11da

ffff

Description:

The contents of register 'f' are dec-

remented. If 'd' is 0, the result is

placed in W. If 'd' is 1, the result is

placed back in register 'f' (default).

If the result is 0, the next instruc-

tion, which is already fetched, is

discarded, and a NOP is executed

instead, making it a two-cycle

instruction. If ’a’ is 0, the Access

Bank will be selected, overriding

the BSR value. If ’a’ = 1, then the

bank will be selected as per the

BSR value (default).

Words:

Cycles:

1(2)

Note: 3 cycles if skip and followed

by a 2-word instruction.

Q Cycle Activity:

Decode

Read

Process

Data

Write to

destination

If skip:

operation

If skip and followed by 2-word instruction:

operation

Example:

HERE

DECFSZ

CNT, 1, 1

GOTO

LOOP

CONTINUE

Before Instruction

Address (HERE)

After Instruction

CNT

CNT - 1

If CNT

PC =

Address (CONTINUE)

If CNT

≠

PC =

Address (HERE+2)

DCFSNZ

Decrement f, skip if not 0

Syntax:

[

label ] DCFSNZ

f [,d [,a]

Operands:

≤ f ≤ 255

∈ [0,1]

Operation:

(f) – 1

→ dest,

skip if result

≠ 0

Status Affected:

None

Encoding:

0100

11da

ffff

Description:

The contents of register 'f' are dec-

remented. If 'd' is 0, the result is

placed in W. If 'd' is 1, the result is

placed back in register 'f' (default).

If the result is not 0, the next

instruction, which is already

fetched, is discarded, and a NOP is

executed instead, making it a two-

cycle instruction. If ’a’ is 0, the

Access Bank will be selected,

overriding the BSR value. If ’a’ = 1,

then the bank will be selected as

per the BSR value (default).

Words:

Cycles:

1(2)

Note: 3 cycles if skip and followed

by a 2-word instruction.

Q Cycle Activity:

Decode

Read

Process

Data

Write to

destination

If skip:

operation

If skip and followed by 2-word instruction:

operation

Example:

HERE

DCFSNZ

TEMP, 1, 0

ZERO

NZERO

Before Instruction

TEMP

After Instruction

TEMP

TEMP - 1,

If TEMP

Address (ZERO)

If TEMP

≠

Address (NZERO)

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