Nick, nice decoding of the numbers there. I can set the pixel clock to
110ns per pixel (9.09 MHz), but since this is a free parameter in the
Raspberry Pi it should also work with the 20MHz that I originally
specified, right?
Best wishes
Jens
On 2022-02-20 10:52 p.m., Nick Sargeant wrote:
Comparing the timings in the picture and going for common
denominators, you can see that the front porch and back porch are (4
units of 660 ns) long, hsync is (7 units of 660ns) long, video itself
is (64 units of 660ns) long. So I would offer that there is a 64
character display, where each character is made up of ?6 pixels. So,
if you use a pixel rate of 110ns, then use those numbers for the
parameters of dpi timings, and you should get there. Front porch, back
porch are 24 pixels each, hsync is 42 pixels, active pixels is 384, ...
On Monday, 21 February 2022 at 01:58:19 UTC nixiebunny wrote:
Jens,
The horizontal line timing is incorrect. This is why the image is
diagonal.
The numbers that you provided do not specify the horizontal line
total time or frequency.
The monitor requires 52 microseconds or 19.2 kHz.
You need to find a way to specify this, perhaps it is the
character count or pixel count and the pixel frequency.
On Sun, Feb 20, 2022, 6:26 PM jb-electronics
<[email protected]> wrote:
Dear all,
Apologies for the off topic question, but I know there are
some CRT experts in our group and I have been banging my head
on this one for a while.
I picked up a cute 6" monochrome CRT module which accepts TTL
video. This is the timing chart:
My goal is to run this thing using the DPI module of the
Raspberry Pi. But for all of that to work I have to specify
certain parameters and pass them along to the DPI module, and
here is what I read off the sheet:
* h sync: 4.615 us
* h front porch: 2.637 us
* h back porch: 2.637 us
* v sync: 0.208 ms
* v front porch: 0.209 ms
* v back porch: 2.917 ms
* active lines: 256
I have verified that at least the vertical signal timing is
implemented correctly, my scope is a tad too slow to resolve
the horizontal timing. But there appears only gibberish on the
screen, highly distorted text. Here is how it looks like:
http://jb-electronics.de/tmp/screen01.jpg
And this is what it should be (composite video output on my
Apple IIc monitor) for the same "scene":
http://jb-electronics.de/tmp/screen02.jpg
Can somebody tell me if I am on the right track here, or if
there is a fundamental mistake somewhere in the numbers I read
off? Your help is very much appreciated.
Best wishes
Jens
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