90s2313 video generator

[DrWhoF]

vsync 90s2313

I am trying to build video generator based on 90S2313:
https://www.serasidis.gr/circuits/colour_bar_gen/colour_bar_gen.htm
The problem I have is that video signal is weak and black and white.
Why?

 

[Pavel_S]

Check output voltages , it should be 1Vpp. Check assembly and resistor values.

As I know, impedances for video devices are 75Ω but in this circuit are not.

 

[IanP]

Most likely the 75Ω input impedance of your TV-Monitor has attenuated the magnitude of the video signal ..
If the monitor has a switch that selects between High-Impedance and 75Ω, set it to High-Impedance ..
Otherwise you will need a buffer ..
Attached is an example of a single BJT unity gain amplifier/buffer ..

Regards,
IanP

 

[DrWhoF]

Hi IanP
I added your bufferand and now I have 1.2Vpp video signal going into TV monitor but the picture is black and white.
Why is it B&W?

 

[Tricky Dicky]

I have the same problem which is B&W picture and so far couldn't get any answer even from this source:
**broken link removed**
I still hope that someone can help us to solve this puzzle: why I(we) can't generate colour picture?

Tricky Dicky

 

[IanP]

Try to “play” with the load capacitors around the 17.734MHz crystal ..
For example, connect 100pF (or even more) to pin 4 (XTAL2) and 47pF to pin 5 (XTAL1) ..

Regards,
IanP

 

[Tricky Dicky]

This forum is great.
I have been asking for solution to this problem for months.

BINGO. Only selecting different load capacitors (120pF + 47pF) and color is ON.
IanP, that was brilliant suggestion !!!

Thanks a lot.

 

[IanP]

Very glad to hear that the diagnosis was correct ..

Regards,
IanP

 

[DrWhoF]

Yeah, it is working :!:
I replaced 2x22pF with 150pF and 47pF.
Now, how to make the whole screen blue :?:

 

[IanP]

First of all, if you intend to do this job properly you should use the second version of software that has implemented all required elements of a video frame, that is, H-sync, V-sync, equalizations and all that stuff ..

Secondly, to produce single-colour screen you have to program the microcontroller to continuously generate colour carrier for the duration of whole horizontal line ..
This will require a lot of instructions (see code - 4 OUT instuctions form one cycle) with no other operation(s) in between ..

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

If you can, do your homework and calculate how many of these cycles is needed to fill one horizontal line and how this is related to the size of the AT90S2313's program memory, in other words, will the complete code fit into it, or not ..

Regards,
IanP

 

[DrWhoF]

I am not very familiar with 90S2313.
Do you think the code will not fit into flash?

 

[IanP]

The AT90S2313 has "only" 2k of program memory and it is NOT big enough for this application (blue screen) ..
I recon it could be done if the program memory were somewhere close to 4k ..

If you still would like to use the same code you have to “stick” with the same family ..
Investigate if, for example, the AT90S8515 or atmega8515 can be “over-clocked” at 17MHz ..
http://dhost.info/ky3orr/funkcje/do...link=dokumentacje/at90s8515_na_atmega8515.pdf

Regards,
IanP

 

[DrWhoF]

Thanks for your help.
I think I can use screen with color bars and 90S2313.

DrWho