Explanation of PIC mid-range microcontroller assembly instructions (1)

NOP null Operation Command

Syntax: NOP

Operand: None

Execution time: one instruction cycle

Execution Process: Except for consuming one instruction cycle, it has no impact. Therefore, it is usually used as a delay.

Status flag impact: None

Note: The instruction operation does not involve any operands and does not affect the content and status of any registers. Therefore, it is generally used as a delay.

Command example: BSF portb, 0; portb's 0th-bit output high level (1)

NOP; latency to make the level stable

Movwf transfers W register content to the data register

Syntax: movwf F

Operand: F is the low 7-bit address of the data register (0x00 ~ 0x7f)

Execution time: one instruction cycle

Execution Process: Transfers W register content to f data register, W register content remains unchanged, similar to copy

Status flag impact: None

Note: This command is used to assign values to data registers.

Command example:

Movlw 0x55; W register value assignment

Movwf data; W register value transmitted to data

Data = 0x55

Clrw W register content cleared 0

Syntax: clrw

Operand: None

Execution time: one instruction cycle

Execution Process: 0x00 → W

1 → Z

Status flag impact: Z

Note: This command clears W register content, and sets the 0 Mark Z of the parallel position.

In addition, you can use movlw 0x00 to set the W register content to 0, but this command does not affect the 0 Mark Z.

Command example: clrw; W = 0, Z = 1

Clear clrf data register content

Syntax: clrf F

Operand: F is the low 7-bit address of the data register (0x00 ~ 0x7f)

Execution time: one instruction cycle

Execution Process: 0x00 → F

1 → Z

Status flag impact: Z

Note: The command is used to reset the data register, and the parallel position 0 indicates Z.

Command example: clrf trisb; all I/O pins of port B are set as output

Subwf subtract W register content from the data register content

Syntax: subwf F, d

Operand: F is the low 7-bit address of the data register (0x00 ~ 0x7f)

D is the low 7-bit address of the destination register (0x00 ~ 0x7f)

When d = F, the result is placed in the f data register, and the W register content remains unchanged.

When d = W, the result is placed in W register, and the data register F content remains unchanged.

Execution time: one instruction cycle

Execution Process: [f]-[w] → D

Status flag impact: Z DC C

Note: The w register is a subtrahend in this command.

When [f] = [w], the result of subtraction is 0, then z = 1

If [f]> [w] does not take place, c = 1

When [f] <[w], a bid occurs, c = 0

In fact, in the PIC single-chip microcomputer, this command is to obtain the complement code for the W register content and then add it to the subtrahend. Therefore, it is different from other single-chip microcomputer when determining whether there is a bid. Please note that

Command example:

Movlw 0x23; W = 0x23

Movwf TMP; TMP = 0x23

Movlw 0x32; W = 0x32

Subwf TMP, W; TMP-W: Save the result to W, W = 0xf1, TMP = 0x23

; Process: TMP = 0x23, W find the completion code is 0xcd, So 0x23 + 0xcd = 0xf1, And because TMP <W, c = 0