Moving Data
Chapter 5 – PIC Notes
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Department of Computer Systems Engineering
Aims and Outcomes
• Aims
• To introduce commands used to move data between registers
• To introduce the use of the TRIS registers
• Outcomes
• After completing this chapter you should be able to:
• Set and clear bits in file registers using the BSF and BCF instructions
• Move data between file registers using the MOVF, MOVLW, MOVWF instructions
• Implement the GOTO instruction
• Implement the INCF, DECF, CLRF and CLRW instructions
• Discuss and use the EQU and ORG compiler directives
• Use the TRIS registers to correctly setup the ports
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Numerical Prefixes
• Decimal
• d’xx’
• Data values can be represented in the • .’xx’
following four formats • xxd
• Confirm the methods your compiler / • Hexadecimal
IDE uses • h’xx’
• 0xAA – Where AA is the hex number
• $F7 – Where F7 is the hex number
• F7h
• Binary
• b’xxxxxxxx’
• 0bxxxxxxxx
• xxxxxxxxb
• ASCII
• ‘A’
• A’…’
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Introduction to Instructions
• Instructions are used to create a programs
• Instructions are divided into
• Byte-oriented operations
• Bit-oriented operations
• Literal and control operations
Figure 15.2: General Format for Instructions
(Microchip, 2003. p108)
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OPCODE field Description
• The instruction operands Field Description
indicates the type of data to be f Register file address
used by a specific instruction w Working register
b Bit address within an 8-bit
• Most of the time it can also be file register
deduced from the command k Literal field, constant or
being used label
d Destination select
• MOVLW k d=0: Store results in w
d=1: Store results in f
default is: d=1
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Instruction Format
• Instructions are 14-bit words divided
into OPCODES and operands
• OPCODES indicate the instruction
type
• Operands specify the operation of
the instruction
Figure 15.1: General Format for Instructions Faculty of Information and Communication Technology
(Microchip, 2003. p107) Department of Computer Systems Engineering
Instruction Construction Example
Figure 15.2: PIC16F62X
Instruction Set (Microchip, 2003.
p108)
• The opcodes for all the instructions are at the back of the PIC notes
and also in the datasheet.
• The included table only shows the literal and control operations.
• As an example let us use the following instruction: GOTO 10h
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Instruction Construction: GOTO 10h
Figure 15.2: PIC16F62X
Instruction Set (Microchip, 2003.
p108)
• The OPCODE for the GOTO command is: 1012
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Instruction Construction: GOTO 10h
Figure 15.2: PIC16F62X
Instruction Set (Microchip, 2003.
p108)
• An binary equivalent address must be provided: kkk kkkk kkkk2
• The address 1016 in binary is: 0001 00002
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Instruction Construction: GOTO 10h
Figure 15.2: PIC16F62X
Instruction Set (Microchip, 2003.
p108)
• The machine code for the command: GOTO 10h, is:
• 101 000 0001 00002
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W Register
• The Working Register (W) can be seen as a gateway through which all
the data travels towards its new destination
• W is an 8-bit register only accessible by the ALU i.e. does not have a
memory location we can access
• W can be the destination of data movement when using some
commands and setting the destination bit (d) to 1
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BSF f,b
• Bit Set File is used to SET (change bit to ‘1’) a specific bit inside a file
register
• f = file address
• b = bit position in the file address
• It can only set 1 bit and not set multiple bits
(Spies, 2020. p41)
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BCF f,b
• Bit Clear File is used to CLEAR (change bit to ‘0’) a specific bit inside a
file register
• f = file address
• b = bit position in the file address
• It can only clear 1 bit and not clear multiple bits
(Spies, 2020. p41)
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MOVLW k
• Copies a literal value (k) into the working register
• A literal value can be seen as a physical value the programmer wants
to load into the microcontroller
• k = literal value that must be copied to the working register
(Spies, 2020. p41)
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MOVWF f
• Copy the value of the working register into file register f
• f = address of the file wherein the value needs to be loaded
(Spies, 2020. p41)
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MOVF f,d
• The content of the selected
register, f, is copied to a
destination depending on the (Spies, 2020. p41)
value of d
• f = file that must be copied from
• d = 0 – destination is the w
register
• d = 1 – destination is back to the (Spies, 2020. p41)
file
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GOTO k
• This is used to branch off to a specific label
• GOTO is a two-cycle instruction
• k = label name whereto program must branch
(Spies, 2020. p41)
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INCF f,d
• Increment the content of file f, by 1
• Save the answer into either the w register or the file itself depending on
the value of d
• d=0 – Destination is w register
• d=1 – Destination is the file register, f
(Spies, 2020. p41)
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DECF f,d
• Decrement the content of file f, by 1
• Save the answer into either the w register or the file itself depending on
the value of d
• d=0 – Destination is w register
• d=1 – Destination is the file register, f
(Spies, 2020. p41)
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CLRF f
• Clears the value of register f
(Spies, 2020. p41)
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CLRW
• Clears the value of the w register
• It does the same as the shown MOVLW instruction
(Spies, 2020. p41)
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PORT Setup Example
• Suppose we want to use RB0 to
connect an LED to flash
• Steps
• Go to Bank 1
• Change RB0 to an output pin
• Go back to Bank 0
(Spies, 2020. p41)
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Moving Data to a PORT
• A PORT is associated with a
memory location
• Writing data to a port is the
same as writing data to a
memory location
• The code shows how to flash an (Spies, 2020. p41)
LED connected to RB2
• Remember that all the other bits
on the port will be cleared!
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Compiler Directive -
EQU
• It is used to substitute text
(create an alias)
• The compiler does not
understand the meaning it just
replaces the equated value
when compiling
• Some compilers might already
have the reserved
registers/pins equated (Spies, 2020. p41)
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Compiler Directive -
ORG
• ORG is used to compile
program code into specific (Spies, 2020. p41)
memory location
• Its primarily used to skip over
the interrupt vector located at
h’04’
• Look at the memory after the
compilation
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End of Chapter
Any questions?
Faculty of Information and Communication Technology
Department of Computer Systems Engineering
References
• Microchip, 2003. PIC16F62X Data Sheet. [online] Microchip
Technology. Available at:
<https://ww1.microchip.com/downloads/en/DeviceDoc/40300c.pdf>
[Accessed 4 June 2020].
• Spies, J., 2020. An Introduction To Microcontroller Concepts Using The
PIC Microcontroller.
Faculty of Information and Communication Technology
Department of Computer Systems Engineering
