Vasilis Video Color Bar Generator (ASM)

AVR composite PAL colour bar generator

After lof of reading books, articles and discussions with lot of electronic technicians, finaly I did it. I make an 6 colour bar generator entire-in-software with AT90s2313-10 overclocked at 17.734475 MHz !!!

Designed by: Serasidis Vasilis

I start this project 3 weeks ago, because I was wonder " is that possible, some AVR MCU to create simple colour bars? " At the beginning I believed that its easy. So, I ask some people who they knew more about PAL composite video signal. Some of them told me that is impossible to product color entire-in-software with AVR MCU (microcontroller) because there is not enough power (frequency).

The first idea they was to work with 8.867238 MHz crystal (2 times the color carrier). When I read more about PAL video composite signal creation, I saw that, if you want to product colors entire-in-software you must to create the color-carrier (4.43 MHz), to change 4 times the phase of color-carrier (one time for each color), to show 4 colours. Except that, you have to change the color-burst from 135 deg to 135+90= 225 deg.

So, the 8.86 MHz its not enough, that`s why I used 17.7 MHz crystal (4 times the color carrier). The only easy is to create the white and the black bar, the rest of this project, beleave me, its not easy.

The timing (clock cycles) of any instruction is very important for the phase-shift of the color-carrier and color-burst signals. Calculate the cycles before add or remove any instruction.

The circuit (See Attached File)

The circuit it is constituted by AT90s2313 running at 17.734475 MHz (overclocked) and one, 5 bits DA converter (R2R-ladder) with 10 resistors.

I know, its not good to overclocking 77 % up from the working frequency of the MCU, but for a few hour, nothing wrong it will happen.

Programm the MCU with colour_bar_gen.hex that its included in colour_bar_gen.zip file, connect it on composite video connector (or scart adapter) of your TV, power-on the circuit and you will see on TV, 6 vertical bars, 4 in color, 1 white and 1 black.

I don't make any explanation about "how does the PAL video signal its working" because nor and i I understood exactly how does its work. Thats why my circuit have some problems with color-hue. May be some one of you, have the knowledge and the time, to continue this project..

CODE

;
;**************************************************************************************************************************************************
;*
;* PAL VERTICAL COLOUR BAR GENERATOR
;*
;* Author: Serasidis Vasilis
;* Writed: 14-08-2003 with AVR Studio 4.02
;* Version: 0.1 beta
;* Target: AT90S2313-10 overclocked at 17.734475 MHz
;* Web site: http://www.serasidis.gr
;* eMail: info@serasidis,gr
;*
;*
;* This PAL vertical colour bar genarator based on AT90s2313-10 MCU, overclocked at 17.734475 MHz !!!
;* because there is no AT90Sxxxx at this frequency. Near to 17 MHz is AT90S1200-16 but i could`n find it on the market.
;* For Analog to Digital converter i used R2R-ladders with 500 ohm and 1 Kohm resistors connected to PortD.
;*
;* This source code its not complete. Its working, but the colour-hue its not the same in all TVs.
;* The colors from the left of the screen are: white, magenta, orange, green, blue and black.
;* I leave this source code, to continue it, someone else.
;* I dont make any economy to the flash-memory. I leave the code extended, for modifications.
;*
;* Remember!!!
;* - The timing of the instructions is very important.
;* - Do not remove any 'Nop' intruction without replace it with someone else instruction.
;*
;* Inform me if you improve this source code
;* Good luck
;*
;***********************************************************************************************************************************************
;
;
;
;
;
.include"2313def.inc"
.def temp =r16
.def delay =r17
.def burst =r18
.def zero =r22
.def one =r23
.def up_color =r20
.def down_color =r26
.def color_bar =r27
.def wreg2 =r30
.def up =r28

ldi temp,RAMEND
out SPL,temp;Init Stack Pointer

ldi temp, 0b01111111 ;set port D bits to outputs
out DDRD, temp

;----------------------------------------------------------------------
reset:
clr zero ;zero voltage level
ldi up,30 ;high voltage level (1.2V - white color)
ldi burst,1 ;
ldi one,8 ;low voltage level (0.2V - black color)
ldi up_color,10;High level for color carrier (1V)
ldi down_color,6;Low level for color carrier (0.38V)
ldi wreg2,6

start: ldi color_bar,4;Number of color bars (4 color bars + 1 white + 1 black)
ldi one,8
out portd,one

ldi up_color,10 ;set the up-voltage level for color burst
ldi down_color,6;set the down-voltage level for color burst
ldi one,8 ;set the midle-voltage level for color burst

ldi delay,2
rcall again ;17 cycles delay

out portd,zero ;start the orizontal sinchronization
rcall delay2 ;delay 6.44uS (115 cycles. 1 cycle=0.056uS at 17,734475 MHz)

out portd,one
nop
nop

ldi delay,2
rcall again ;17 cycles delay

dec burst ;starting color-burst with 135 deg the 1st scan-line. To the 2th scan-line add 90 deg more. Sum 90+135=225 deg.
breq color_burst;If its on the first scan-line, go to 'color_burst'
ldi burst,1 ;if its on the 2th scan-line...
nop ;
nop ; invert 90 deg (sum 135+90=225 deg)

color_burst:
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one

out portd,up ;Show the white color (1st color bar)
rcall delay

ldi up_color,29 ;set the up-voltage level for color carrier
ldi down_color,10 ;set the down-voltage level for color carrier
ldi one,14 ;set the midle-voltage level for color carrier
nop

color_carrier:
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one

out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one

out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one

out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one
out portd,down_color
out portd,one
out portd,up_color
out portd,one ;146 cycles
out portd,down_color

dec color_bar ;check if is the 5th color-bar (blue)
breq start2 ;if yes, go to start again from the beginning
rjmp color_carrier;if not, go to show the next color-bar (151 cycles)
;------------------

start2: out portd,wreg2 ;Show the black color (6th color bar)
rcall delay
rjmp start
;--------------------

;
;--------------- Delay ----
delay:;delay 152 cycles (51,072uS/6 bars = 8,512uS = 152 cycles)
ldi delay,63;55;48
again: dec delay
brne again
ret
;-------------------------
delay2:;delay 115 cycles
ldi delay,24
again2: dec delay
brne again2
ret