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
Dec 17, 2015
Ch. 2- Assembly Lang - PIC
The PIC Microcontroller and Embedded Systems: Using Assembly and C for PIC18By Muhammad Ali Mazidi, Rolin McKinlay, Danny Causey
• http://microdigitaled.com/PIC/Software/PIC_tools.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
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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
languageMOVLW 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 5h• MOVLW 05h• MOVLW 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 hundredmore 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 + GPR• PIC12F508 32 bytes 7 25• PIC16… 80 12 68• PIC18F452 1792 256 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 55H ;WREG = 55H
MOVWF PORTB ;copy WREG to Port-B
MOVWF PORTC ;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=99HMOVWF 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 ; =15h + [WREG]
• ADDWF fileReg, D ; =[WREG] + [fileReg]
• 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