old graphical interface to screen connection - Page 1
Forum section: electronics / general

author: Wawavoun
author_rank: Regular Contributor
timestamp: May 11, 2022, 08:11:53 am
content: Hello there,I am on the project to rebuild a 'high' resolution color graphical interface (description in several parts into Elektor n° 87 to 94) for my Junior Computer.These boards provide the video signal at TTL level (R+G+B+CSync).The pixel clock is 12 Mhz, usually vga monitor dont handle so low frequency....What is the best and simplest solution for connecting that to a lcd tv (scart ?) or to a vga monitor ? If I can find something ready to use...Thanks for help.Philippe

author: Ian.M
author_rank: Super Contributor
timestamp: May 11, 2022, 08:26:55 am
content: I dug up the first page of the article in question, and it says 64 us per line and a 50 Hz frame rate. That's 15.625KHz line frequency, so its RGB component video using PAL/SECAM sync timings.It should connect direct to any European TV with a SCART connector. If you want to use it with a SVGA monitor you'd need to run its output through a scanrate converter.

author: Wawavoun
author_rank: Regular Contributor
timestamp: May 11, 2022, 08:33:12 am
content: But then I have to made level converters...Scart is not for TTL level.

author: PKTKS
author_rank: Super Contributor
timestamp: May 11, 2022, 08:50:53 am
content: Quote from: Wawavoun on May 11, 2022, 08:33:12 amAccepts SCART direct input and outputs RGB signalthere is also a dedicated NTSC version of this chipI have a half dozenPaul

author: Ian.M
author_rank: Super Contributor
timestamp: May 11, 2022, 09:00:29 am
content: For analog video, peak white or single R,G or B component should be +1.0V, black +0.3V, and if it has sync (sync on green or composite video) 0V for the sync pulses.Usually, TTL RGB => SCART RGB was a simple series resistor to form an attenuator with the 75 ohm SCART RGB input impedance, The resistor was typically somewhere between 180 to 330 ohms depending on how high the TTL RGB output swung under load.If the black level overdrive (dropping to 0V rather than 0.3V) is a problem, or if you need to add in an intensity signal, it gets more complex and you'll probably have to build a proper level converter.

author: PKTKS
author_rank: Super Contributor
timestamp: May 11, 2022, 09:21:26 am
content: Quote from: Ian.M on May 11, 2022, 09:00:29 amSimple direct SCART interface i ve used couple of times with the chip above...Paul

author: PKTKS
author_rank: Super Contributor
timestamp: May 11, 2022, 09:35:57 am
content: better to add the insertion matrix to avoid confusion how the chip interfaces...cheersPaul

author: amyk
author_rank: Super Contributor
timestamp: May 12, 2022, 01:48:03 am
content: Quote from: Wawavoun on May 11, 2022, 08:11:53 amPixel clock is only indirectly related to the horizontal/vertical timings. You could absolutely make a VGA monitor sync to a signal with a pixel clock of 12 MHz as long as the hsync/vsync frequencies are the same, but the resolution will be lower. In fact when displaying CGA modes the VGA halves the pixel clock so you get 320 instead of 640 pixels in the active area.

author: Wawavoun
author_rank: Regular Contributor
timestamp: May 24, 2022, 06:22:46 am
content: Hello there,Thanks for all the tips for scart connection. I will give a try as soon as I get the color extension working.I continue to work on this hi res graphical board based on a Thomson EF9367. She is now more or less working.They can work into 512 pixels (H) x 256 (V) non interlaced or into 512 x 512 interlaced.In the first mode no problem at all, the lcd tv used via composite video input works well and picture is good.Into 512x512 interlaced mode the top of the display is on the bottom of the screen (see picture).The board is initialized by a kind of driver that I have only in binary format.I give a look to the EF9367 datasheet and I dont find any information about video timing (front porche, back porche etc...) controls like for a Motorola 6845 or Nec 7220 for example.What is the best way to improve the situation ?Thanks, regards.Philippe