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Look-up tables

Look-up tables. Macros. A macro is a grouping of instructions, defined by the programmer and given a name. When the source code is assembled, the macro is expanded out into the original instructions that made it up. The macro itself is contained within the directives macro and endm . Eg:

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Look-up tables

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  1. Look-up tables

  2. Macros • A macro is a grouping of instructions, defined by the programmer and given a name. • When the source code is assembled, the macro is expanded out into the original instructions that made it up. • The macro itself is contained within the directives macro and endm. • Eg: • Bank1 macro • Bsf STATUS,RP0 • endm

  3. Puzzle • Give output of the following instructions • Bcf STATUS,RP0 ;Select bank0 • Movlw 33h • Movwf TRISA • Output???

  4. Output • PORTA = 33h

  5. Bank Seletion • Ensure you have chosen correct bank in data memory • In the above program, if you want to input some value in trisa, you should select bank 1 (bsf status,5).

  6. Context saving (Intservice ISR) • ;ISR • ;PUSH OPERATION • movwf w_temp ;Copy W to W_TEMP register, • swapf status,0 ;Swap status to be saved into W • movwf status_temp ;Save status to STATUS_TEMP register • ;Interrupt Service Routine • ... • actual ISR goes here • ... • ;POP OPERATION • swapf status_temp,0 ;Swap nibbles in STATUS_TEMP register • ;and place result into W • movwf status ;Move W into STATUS register ;sets • ;bank to original state • swapf w_temp,1 ;Swap nibbles in W_TEMP and keep result in • ;W_TEMP • swapf w_temp,0 ;Swap nibbles in W_TEMP and place result into W • ... • clear interrupt flag(s) here • ... • retfie

  7. Cblock assembler directive • Blnkcnt equ 20h • Num1 equ 21h • Num2 equ 22h • Counth equ 23h • Countl equ 24h • Cblock 20h • Blnkcnt • Num1 • Num2 • Counth • Countl • Endc =

  8. Assembler directives • While the Assembler program is written for the target microcontroller, it has to be processed by the Assembler first. • To aid this process and make it more powerful and flexible, a way is needed of passing information and instructions to the Assembler, which it recognizes as being for its attention only. • These instructions are called Assembler directives.

  9. Number representation

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