I'm drunk but I still got 4-bit GRAY SCALE BABY!

cbmeeks

hahaha..

yeah, I've been drinking. Man, I have to be the best drunkin EE amateur on the planet...LMAO.

For those that don't know...I've spent a lot of time in the XGamestation forums building different types of circuits for my homebrew computer. Anyway, I built a video circuit a while back using a PIC16F88 so now, I have converted it to an SX28 running 50MIPS. Anyway, I am displaying 16 shades of gray (including black,white and sync) on an NTSC monitor.

I built a 4-bit DAC using resistors (R2R network) and I now have 16 shades of gray! Well, actually, I have 13 shades of gray because Sync s 0, black is 1, and white is 15.

Anyway, it's beautiful...if I can get my freakin' camera to work, I will take some pics. :-D

Here is the source code....and yes, I stole Andre's DELAY macro but it's so damn good, why try and re-invent it?

;=======================================================================
;TITLE:         ntsc01
;
;PURPOSE:       Create purty pictures in assembly language
;
;AUTHOR:        cbmeeks
;
;CONNECTIONS:
;  RB.0 - RB.3 to R2R ladder
;
;DETAILS:
;=======================================================================


    ;-------------------------- DEVICE DIRECTIVES --------------------------
    DEVICE SX28,OSCHS2,TURBO
    FREQ 50_000_000

    IFDEF __SASM ;SASM Directives
    DEVICE STACKX,OPTIONX
    IRC_CAL IRC_SLOW

    ELSE ;Parallax Assember Directives
    DEVICE STACKX_OPTIONX
    ENDIF

    RESET Initialize

    ;------------------------------ VARIABLES ------------------------------

    SYNC equ %00000000
    BLACK equ %00000001
    WHITE equ %00001111

    GRAY2 equ 2
    GRAY3 equ 3
    GRAY4 equ 4
    GRAY5 equ 5
    GRAY6 equ 6
    GRAY7 equ 7
    GRAY8 equ 8
    GRAY9 equ 9
    GRAY10 equ 10
    GRAY11 equ 11
    GRAY12 equ 12
    GRAY13 equ 13
    GRAY14 equ 14

    CLK_SCALE equ 5 ; used to make calling the DELAY macro easier
    ; set this to the frequency / 10,000,000
    counter DS 1 ; general counter
    counter2 DS 1 ; general counter


    ; **** MACROS *****************************************************************

    ; /////////////////////////////////////////////////////////////////////////////
    DELAY MACRO clocks
    ; Thanks to Andre' Lamoth for this delay routine
    ; this macro can handle large delays up to 25,500 cycles, so to call it use the following
    ; constructions

    ; cycle delay
    ; DELAY(number_of_clocks)

    ; for 80 mhz clock, microsecond parameters
    ; DELAY(80*microseconds)
    ; example you want a 4.5 uS delay
    ; 80*4.5 = 360
    ; DELAY(360)

    ; the preprocessor can NOT do floating point math, so another construction would be to scale
    ; all values by 10 then multiply by 8 rather than 80, for example, a 4.5 uS delay could be
    ; written
    ; DELAY(8*45)
    ; which is a little more intuitive

    ; first compute fractional remainder of 10 and delay
    IF (((clocks) // 10) > 0)

    ; first 3 clock chunks
    REPT (((clocks) // 10)/3)
    JMP $ + 1
    ENDR

    ; now the remainder if any

    REPT (((clocks) // 10)//3)
    NOP
    ENDR
    ENDIF

    ; next multiples of 100
    IF (((clocks) / 100) >= 1)

    ; delay 100*(clocks/100), loop equals 100, therefore 1*(clocks/100) iterations
    mov counter, #((clocks)/100) ; (2)
    :Loop

    mov counter2, #24 ; (2)
    :Loop100
    djnz counter2, :Loop100 ; (4/2)

    djnz counter, :Loop ; (4/2)

    ENDIF


    ; last compute whole multiples of 10, and delay
    IF (( ((clocks) // 100) / 10) >= 1)

    ; delay 10*(clocks/10), loop equals 10, therefore (clocks/10) iterations
    mov counter, #( ((clocks) // 100) / 10) ; (2)
    :Loop2
    jmp $ + 1 ; (3)
    jmp $ + 1 ; (3)
    djnz counter, :Loop2 ; (4/2)

    ENDIF

    ENDM


    ;------------------------ INITIALIZATION ROUTINE -----------------------

    Initialize
    ;Configure port settings
    mov rb, #%00000000 ;Port A output zero
    mov !rb,#%00000000 ;Port A all output

    ;---------------------------- MAIN PROGRAM -----------------------------

    Main

    ; front porch 1.5us
    mov rb, #BLACK ;2 cycles - black
    DELAY (CLK_SCALE*15-2)

    ; hsync 4.7us
    mov rb, #SYNC ;2 cycles - sync
    DELAY (CLK_SCALE*47 - 2)

    ;delay for old TV's 3.8us
    mov rb, #BLACK ; 2 cycles - black
    DELAY (CLK_SCALE*38 - 2)

    ;begin scanline 10us


    mov rb, #WHITE
    DELAY (CLK_SCALE*30 - 2) ;3us
    mov rb, #GRAY14
    DELAY (CLK_SCALE*30 - 2) ;3us
    mov rb, #GRAY13
    DELAY (CLK_SCALE*30 - 2) ;3us
    mov rb, #GRAY12
    DELAY (CLK_SCALE*30 - 2) ;3us
    mov rb, #GRAY11
    DELAY (CLK_SCALE*30 - 2) ;3us
    mov rb, #GRAY10
    DELAY (CLK_SCALE*30 - 2) ;3us
    mov rb, #GRAY9
    DELAY (CLK_SCALE*30 - 2) ;3us
    mov rb, #GRAY8
    DELAY (CLK_SCALE*30 - 2) ;3us
    mov rb, #GRAY7
    DELAY (CLK_SCALE*30 - 2) ;3us
    mov rb, #GRAY6
    DELAY (CLK_SCALE*30 - 2) ;3us
    mov rb, #GRAY5
    DELAY (CLK_SCALE*30 - 2) ;3us
    mov rb, #GRAY4
    DELAY (CLK_SCALE*30 - 2) ;3us
    mov rb, #GRAY3
    DELAY (CLK_SCALE*30 - 2) ;3us
    mov rb, #GRAY2
    DELAY (CLK_SCALE*30 - 2) ;3us

    mov rb, #BLACK
    DELAY (CLK_SCALE*115 - 2) ;11.5us


    jmp Main ;goto main

Hope this helps someone.

WOOOHOOO!!!!

cbmeeks