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