Homework 2 Example...

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Mike M
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Homework 2 Example...

Post by Mike M » Sun Jan 06, 2013 1:17 pm

I think homework assignment #2 is very interesting because it involves animating or moving a single dot around the outside edge of the 8x8 matrix. I would love to see what other people come up with because I imagine there are hundreds of different ways to write a program for this assignment. Here's how I did it.

After thinking about the assignment awhile I realized that I don't have to refresh all eight columns of the display as I did in homework assignment #1. All I really had to do was display a single dot at a certain column and row position for some length of time before going on to the next dot. Since both column and row position can be represented by a three bit value (0 through 7), I realized I could easily represent any particular dot location on the display as a single packed BCD byte with the row value in the high nibble and the column value in the low nibble. For example, a packed BCD value of 0x70 would be used to represent the top right dot on the display at row 7 and column 0.

I built a table to hold the packed BCD dot position for all twenty eight dots that occupy the outer edge positions on the display. The table was ordered so that the first table entry is the top left dot position on the display, with subsequent entries containing dot positions that sequentially move the dot in a clock-wise direction around the display. The last table entry is actually a group of instructions that reset the 16 bit table pointer and wrap-around to the beginning of the table.

The main program loop was designed to read a dot position byte from the table, then uses the 'column' nibble in that byte to set the 7442 address and select the column, then converts the 'row' nibble in that byte to a bit mask which, once written to PORTB, will display the dot. The dot is displayed for 250 msecs before repeating the loop to display the next dot.

The program uses 74 words of program memory and 5 bytes of RAM. As with my homework #1 example, this example for the homework #2 assignment uses techniques that may not be very intuitive for beginning programmers, and I apologize for that. Please don't be afraid to ask questions...

Cheerful regards, Mike

Code: Select all

;  Homework #2: 8x8 Dot Animation      Mike McLaren, 05-Jan-2013  *

   include "P16f648a.inc"

   list st=off          ; turn symbol table off in LST file
   errorlevel -302      ; disable bank warning messages
   radix dec            ; use decimal numbers

;  variables
        cblock 0x20
ptrl                    ; table pointer
ptrh                    ;   "
work                    ; ndx2mask subroutine work variable
mask                    ;   "
delayhi                 ; delay subroutine variable

;  main init                                                      *

        org     0x000
        clrf    STATUS          ; bank 0                          |B0
        movlw   0x07            ;                                 |B0
        movwf   CMCON           ; comparator off, digital I/O     |B0
        bsf     STATUS,RP0      ; bank 1                          |B1
        clrf    TRISA           ; porta all outputs, except RA5   |B1
        clrf    TRISB           ; portb all outputs               |B1
        bcf     STATUS,RP0      ; bank 0                          |B0
        call    tblprep         ; init table pointer              |B0

;  main loop                                                      *

        clrf    PORTB           ; blank the display               |B0
        call    rdtable         ; get packed BCD 'row' & 'col'    |B0
        movwf   PORTA           ; set 7442 addr (select column)   |B0
        call    ndx2mask        ; convert 'row' index to a mask   |B0
        movwf   PORTB           ; display the dot                 |B0
        call    delay           ; delay 250 msecs                 |B0
        incf    ptrl,F          ; bump table ptr                  |B0
        skpnz                   ;   "                             |B0        
        incf    ptrh,F          ;   "                             |B0
        goto    loop            ; branch (loop forever)           |B0


        movf    ptrh,W          ;                                 |B0
        movwf   PCLATH          ;                                 |B0
        movf    ptrl,W          ;                                 |B0
        movwf   PCL             ;                                 |B0


        movwf   work            ; save (use upper nibble 'row')   |B0
        movlw   b'00000100'     ; ndx 2                           |B0
        btfss   work,1+4        ; bit 1 set? no, skip, else       |B0
        movlw   b'00000001'     ; ndx 0                           |B0
        movwf   mask            ;                                 |B0
        btfsc   work,0+4        ; bit 0 set? no, skip, else       |B0
        addwf   mask,F          ; ndx 3 or ndx 1                  |B0
        btfsc   work,2+4        ; bit 2 set? no, skip, else       |B0
        swapf   mask,F          ; ndx 4..7                        |B0
        movf    mask,W          ; wreg = mask                     |B0
        return                  ;                                 |B0

;  delay range: 11..327688 usecs in 5 usec steps (4 MHz clock)
        movlw   high((250000-11)/5)+1
        movwf   delayhi
        movlw   low ((250000-11)/5)
dloop   addlw   -1              ; subtract 5 cycle loop time      |B0
        skpc                    ; borrow? no, skip, else          |B0
        decfsz  delayhi,F       ; done?  yes, skip, else          |B0
        goto    dloop           ; do another 5 cycle loop         |B0
        return                  ;                                 |B0

;  outline table - 28 row/col dot positions in packed BCD format
        retlw   0x77            ; row 7 col 7 (top left)          |B0
        retlw   0x76            ; row 7 col 6                     |B0
        retlw   0x75            ; row 7 col 5                     |B0
        retlw   0x74            ; row 7 col 4                     |B0
        retlw   0x73            ; row 7 col 3                     |B0
        retlw   0x72            ; row 7 col 2                     |B0
        retlw   0x71            ; row 7 col 1                     |B0
        retlw   0x70            ; row 7 col 0 (top right)         |B0
        retlw   0x60            ; row 6 col 0                     |B0
        retlw   0x50            ; row 5 col 0                     |B0
        retlw   0x40            ; row 4 col 0                     |B0
        retlw   0x30            ; row 3 col 0                     |B0
        retlw   0x20            ; row 2 col 0                     |B0
        retlw   0x10            ; row 1 col 0                     |B0
        retlw   0x00            ; row 0 col 0 (bottom right)      |B0
        retlw   0x01            ; row 0 col 1                     |B0
        retlw   0x02            ; row 0 col 2                     |B0
        retlw   0x03            ; row 0 col 3                     |B0
        retlw   0x04            ; row 0 col 4                     |B0
        retlw   0x05            ; row 0 col 5                     |B0
        retlw   0x06            ; row 0 col 6                     |B0
        retlw   0x07            ; row 0 col 7 (bottom left)       |B0
        retlw   0x17            ; row 1 col 7                     |B0
        retlw   0x27            ; row 2 col 7                     |B0
        retlw   0x37            ; row 3 col 7                     |B0
        retlw   0x47            ; row 4 col 7                     |B0
        retlw   0x57            ; row 5 col 7                     |B0
        retlw   0x67            ; row 6 col 7                     |B0
        movlw   boxtbl%256      ; boxtbl address lo               |B0
        movwf   ptrl            ;                                 |B0
        movlw   boxtbl/256      ; boxtbl address hi               |B0
        movwf   ptrh            ;                                 |B0
        goto    rdtable         ;                                 |B0

Last edited by Mike M on Mon Jan 07, 2013 5:08 pm, edited 1 time in total.

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Re: Homework 2 Example...

Post by brad » Sun Jan 06, 2013 6:55 pm

And a great job here again, just like in homework assignment #1 :)

This is quite similar to how I would go about it in Basic. Don't you just love how programming is all about problem solving!

Thanks again for posting these details because I am sure others will find it incredibly useful.

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