1 (edited by Everblue 2014-12-12 18:33:46)

Topic: Video modes

I have a quick question regarding a display issue I am having with the C64 core. I tried the C64 in 50hz mode on a normal TV (using DVI to HDMI adapter) and worked fine. Now I am testing it with a PC monitor which supports 50hz (in fact it works with the Amiga core @ 50hz), but with the C64 core I am having no luck - it only gives a picture if @60hz. Any ideas? Thanks!

Edit: Hmmm it seems the C64 core doesn't have a 50hz mode and the PC monitor is giving issues on interlaced mode.


2 (edited by WoS 2014-12-12 19:13:58)

Re: Video modes

No, there is only the 50Hz mode on the C64 (yet). No way to generate anything with 60Hz...

The difference is only if it is interlaced or non-interlaced (double-scan), this you can set up via OSD or INI file (and nothing else).

edit: I saw I have a typo in the ini (NTSC-like):
" HD 720x480p60"
" SD 720x480i60"
is wrong, the text should be (PAL-like):
" HD 720x576p50"
" SD 720x576i50"
edit done

I suppose your TV supports both variants (and should show them as @50p or @50i), as the generated video is (quite) PAL conform. Thus, you can also use the Replay SVIDEO/Composite output as well on your TV (but only in the interlaced/single-scan mode, of course).

"Pure" PC monitors usually can not handle 50Hz or interlaced modes at all, if not explicitely mentioned (such low V/H sync rates are far below the VESA standard). It may work on "Monitor-TV" solutions or on good old (analogue=VGA) multisync-monitors. So what your monitor tells you for the C64 is wrong, it simply can't handle 50Hz properly (and I assume especially not when the C64 is in interlaced mode, as you said).

It can be just luck that the Amiga uses just a tiny little higher H and/or V frequency so that the monitor still accepts it somehow (or your Amiga runs in NTSC mode?).

By the way, you didn't tell what display connection you used there, as this is not obvious (VGA/DVI-A or HDMI/DVI-D - the OSD of the monitor should provide this information if you use a DVI-I cable).

The frame rate is "given" by the clock the C64 runs with (it is a fixed HW divider). It is already adopted a little to match the HDMI/DVI-D timing, this is all which can be done. Next level is then introducing a full-blown frame buffer and rate converter - which will introduce tearing effects etc. as known by the PC emulators as well, running on (usually) 70Hz and up video cards...
edit2 done

(Btw: I set up a new topic for it, as there might be more to discuss on this...)


Re: Video modes

Quick update: I tried again on my PC monitor and switched to 'p' (via the core's OSD it says "60hz" but I guess that is a mistake?) and did manage to get a picture too smile

With my PC monitor I am suing VGA->DVI-A


Re: Video modes

Ok, very good! Then it can handle the 50Hz V-frequency, but not the ~15kHz H-frequency in interlaced mode. In progressive (double-scan mode) it is then ~31kHz.

Just for completeness:

The H(orizontal)-frequency tells about the time (1/frequency) the monitor has to "draw" one line, the V(ertical)-frequency is similar but about to "draw" the whole frame on the display (although this is still related to good old tube monitors).

The difference between interlaced and progressive mode is that the first "draws" half of the lines within one frame period of 50Hz (so its draws two "half" pictures with this frequency), the second "draws" all lines within one frame period and thus requires the double V-frequency.

Hope this explains it a little...


Re: Video modes

Hi, I have display issues with the C64 core when running it through s-video, the colors are wrong.
Photo coming soon!

Re: Video modes

Very likely the PLL setting of the board in the ini settings. I can't check as I don't have a display to test... :-(

I suppose it is because the clock setup is optimized for HDMI displays, as most of the 8bit devices did not produce a 100% correct PAL signal, but live with the idea that most TV were very tolerant in timing that time...

You may copy the ini file and change some lines in there, a brute-force hack (could happen that video does not sync at all, so pls. keep your original ini):
# sets initial clocking (PLL)
# sets composite/svhs coder, if fitted
# sets video filter for all 3 channels
# dc=250mv, 9MHZ
VFILTER = 0, 0, 3

Please also check no other of the same keywords are set in the new ini, otherwise comment them out with #


7 (edited by spotUP 2016-09-11 23:10:18)

Re: Video modes

Oops. I remembered wrong it seems.
The colors are correct but the screen has a very visible flicker, like you can see the screen updates clearly.
This is with my own ini, would any of those changes you proposed also affect that?

Re: Video modes

It would be nice if the keyboard = ps/2 or amiga would be included in the ini as well. I use an amiga keyboard.

Re: Video modes

I'll have a look Spot, I need to look into your rapp issue also.

10 (edited by yoli 2017-03-17 16:18:23)

Re: Video modes

Is it/will it be possible to have the proper aspect ratio (I guess 4:3) when using a 16:9 screen connected through DVI? Currently the image is stretched to fullscreen.

Update: as mentioned by MikeJ in another thread, the aspect ratio is better handled by setting up the monitor/TV to 4:3.