Ch. 2- Assembly Lang - PIC
The PIC Microcontroller and Embedded
Systems: Using Assembly and C for PIC18
By Muhammad Ali Mazidi, Rolin McKinlay, Danny Causey
• http://microdigitaled.com/PIC/Software/PIC_t
ools.htm
– Install MPLAB
– Install C18
– Read tutorials from http://microdigitaled.com/PIC/PIC_books.htm
Finish!!!?
Now work at home n learn
–
based on the concepts of Intel 8086’s Assembly
Language
=======
Working Register
Only one!
• WREG – Working REGister is same as
Accumulator in other microprocessors
• WREG us used for all arithmetic and logic
instructions
MOVLW instruction
• MOVLW  move 8-bit data into the WREG
reg.
MOVLW
k
 Move literal value of k into WREG
• L  Literally – a number must be used
• Similar to immediate value of 8086’s assembly
language
MOVLW 25H
 Move value 25H into WREG
MOVLW
• ‘L’ stands for literal
• Immediate value concept of other
microprocessor
• ‘W’ for WREG
• MOVLW  move a literal value to WREG reg.
ADDLW
ADDLW
• Add ‘k’ to register WREG
• Put the result back in the WREG
WREG & ALU using literal value
• MOVLW
• MOVLW
• MOVLW
5h
05h
00000101
;in binary
• Moving a value larger than 255 (FF in hex) into
the WREG register will truncate the upper
byte and cause a warning in the .err file
2.2: File Register
•
•
•
•
File register
== data RAM
== data memory
== (general-purpose-reg. + special-function-reg.)
• Data memory space is different from program (code)
memory
Data RAM ==
special-function-reg + general-purpose-reg
• Special-fn.reg. [SFR] for specific functions,
e.g.,
– ALU status
– Timers
– Serial communications
– I/O ports
– ADC
– Etc.
SFR…
• Function of each SFR is fixed by the CPU
designer at the time of the design – as it is
used for control of the microcontroller or
peripheral
• 8-bit registers
• No. of locations in the file reg.?
7 to over a hundred
more timers in a PIC, the more SFR reg. it has
Data RAM ==
special-function-reg + general-purpose-reg
•
•
•
•
GPR / RAM
Used for data storage and scratch pad
8 bits wide
The space that is not allocated for SFRs –
typically is sued for GPR
File reg. size [in bytes]
PIC
File register =
SFR
• PIC12F508
• PIC16…
• PIC18F452
32 bytes
80
1792
7
12
256
+
GPR
25
68
1536
GPR RAM vs. EEPROM
• GPR – internal data storage, used by the CPU
• EEPROM – as an add-on memory, can add
externally to the chip
File register & access bank in PIC18
• PIC18 family can have a max of 4096 (4k = 212)
bytes
• So, address range of the file reg. = 000h ~ FFFh
• File reg. is divided into 256-byte banks
• So, 4069/256
=
16 banks
• At least one bank for the file reg. – called
access bank
• 256-byte access bank  two 128 bytes sections =
GPR & SFR
• The 128 bytes – from locations 00H to 7FH – as
General-purpose reg.
– used for read/write storage
– Scratch pad
– For storing data & parameters by PIC18 programmers &
C compilers
• The other 128 bytes – from locations F80H to FFFH
– as special-function reg.
So far for PIC
• MOVLW
• ADDLW
– Literal
– WREG
2.3: Using instructions with the default
access bank
• MOVWF  it tells the CPU to move (in reality,
copy) the source reg. of WREG – to a
destination in the file reg. (F)
• So, the location (new) in file reg. will have the
same value as reg. WREG.
• F – file reg. – stands for a location in the file reg.
• W – WREG
Move to SFR
• MOVWF
PORTA
; move the contents of WREG  into SFR reg. called PORTA
MOVLW
MOVWF
MOVWF
55H
PORTB
PORTC
;WREG = 55H
;copy WREG to Port-B
;copy WREG to Port-C
.
.
PortB, PortC, and PortD are part of the special function reg.
They can be connected to the I/O pins of the PIC mic.
Move to GPR
• Move [copy] contents of WREG GPR/RAM
MOVLW
99H
;WREG=99H
MOVWF
0H
;move [copy] WREG contents to location 0h
…
- Cant move literal [immediate] values directly into the
general-purpose RAM locations in the PIC18.
- They must be moved there via WREG.
Q: Can literal values directly into SFR?
ADDWF
• ADDLW
15H
• ADDWF
fileReg, D ; =[WREG] + [fileReg]
; =15h + [WREG]
• Sources:
• Content of WREG
• fileReg: Content of file register (special or general)
• Destination: D  indicates destination bit
• If D = 0, destination of the result is WREG, or
• If D = 1, destination is file register