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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