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144
March 16th, 2021 09:00
2408WFP, blurry picture, video vs graphics menu selection
The 2408WFP is an old but really great monitor thanks to all the possible different input sources: DVI-D; HDMI; VGA; RCA Video; S-Video.
I have it hooked to an FPGA board which can create various screen formats over either DVID or HDMI. The HDMI signal differs from the DVID in that there are added "data islands" used to transfer information (AVI packet) and audio.
I cannot easily read the EDID and could not find this information (i.e. modes supported) on the Dell website.
Where can I find this information?
Interestingly the monitor is very forgiving out out-of-spec data formats which I accidently generate when re-compiling my Verilog FPGA source code. I've seen it display low frame rates of 24Hz for example, but in other cases it can't display some of the standard HDMI modes? Strange.
I am trying to convert video from an old 8-bit micro to nice sharp HDMI format. The video is currently 288p format and when connected via the RCA Video input of the 2408 gives a very washed out picture, making it unusable.
As I have experimented to find out which HDMI mode would work best, I see some strange behaviour. Some modes are "sharp" and others are "blurry" or washed out, as if the monitor has switched in a low pass filter. Annoyingly the modes I really want to use are washed out.
This even happens in DVID mode.
Here are the results from the 2408WFP and 2309WFP.
// DELL 2408WFP
FORMAT_640x480p_60Hz // PLL25 -> working 15-Mar-2021
FORMAT_720x480p_60Hz // PLL27 -> working 15-Mar-2021 "Graphics" -> sharp, "Video" -> soft
FORMAT_1440x576i_50Hz // PLL27 -> working 15-Mar-2021 horribly soft video
FORMAT_1440x576p_50Hz // PLL54 -> working 15-Mar-2021 with out of spec pixel clock 50/250MHz (not 54MHz)
FORMAT_2880x240p_60Hz // PLL54 -> working 15-Mar-2021 with out of spec pixel clock 50/250MHz (not 54MHz)
FORMAT_1440x288p_50Hz // PLL27 -> working 15-Mar-2021 horribly soft video
// DELL SP2309W
FORMAT_640x480p_60Hz // PLL25 -> working 15-Mar-2021 "Graphics" -> sharp, "Video" -> soft
FORMAT_720x480p_60Hz // PLL27 -> working 15-Mar-2021 "Graphics" -> sharp, "Video" -> soft
FORMAT_1440x576i_50Hz // PLL27 -> working 15-Mar-2021 brightness difference "Graphics" vs "Video"
FORMAT_1440x576p_50Hz // PLL54 -> working 15-Mar-2021 no obvious difference "Graphics" vs "Video"
FORMAT_2880x240p_60Hz // PLL54 -> NOT working 15-Mar-2021 "not supported by this monitor"
FORMAT_1440x288p_50Hz // PLL27 -> NOT working 15-Mar-2021 "not supported by this monitor"
On the 2408WFP most 50Hz modes are displayed blurry/washed-out.
A discovery was that in some modes switching between "Video" or "Graphics" in the OSD changed between sharp and blurry, however in other modes this OSD choice made no difference. So I couldn't switch off blurry mode in the 50Hz modes (288p is otherwise the ideal mode).
When I tried again on the SP2309W I got a difference in supported modes (OK thats to be expected), but I saw the same behaviour of the OSD "Graphics" vs "Video" setting.
I suspect that this behaviour is hard coded in the firmware, but I would really like
1) an explanation
2) a pointer to a list of all supported DVID and HDMI video modes
3) a way to switch off BLURRY mode !!!
This annoying "feature" might explain why the picture (50Hz 288p) from the RCA Video input was so blurry. There was no way to switch this off. Ironically my old Samsung LED TV gave a better picture from it's RCA Video input socket (but it's too big an bulky for my desk!).
I can sort of see the logic from the designers, "Oh it's a video mode judging by the auto-detected input line and frame sync rates, so let's switch on a really helpful(*) video filter to blur the picture".
(*) No not really helpful at all.
BTW I have the A01 firmware.
This blurry issue spoils an otherwise ideal monitor to use with old 8 bit micros. I'm just surprised that the lower resolution HDMI modes (some at least) are auto-switched to blurry mode too.
migrytech
2 Posts
0
March 16th, 2021 10:00
Just some technical notes about UK (PAL) video format.
Thinking about old CRT TVs, in the UK these are 625 line at 50Hz frame rate. About 576 lines are visible.
The equivalent modern HDMI format is known as 576i where "i" stands for interlaced.
Every 20ms (50Hz) 312 and a half lines are sent. The HALF is important for the interlacing to work. The first half-frame of 312.5 is sent and displayed on the phosphor of the TVs CRT. The next half-frame of 312.5 is sent and displayed BETWEEN the lines previously drawn. I.e each half-frame is offset by half the distance between scan lines. The result is that every 40ms (25Hz) you get 625 lines displayed (OK only 576ish are visible on the CRT). That's also why you see the flicker since the effective frame rate is only 25Hz. It was a clever way to get higher resolution with less bandwidth.
Old home computers of the 1980s often used the home TV through the aerial socket for a video display. Due to the complexity of creating a fully interlaced picture, they CHEATED, and generated both half-frames the same, with only 312 or 313 lines. So the TV did not interlace. But given the poor vertical resolution of old video consoles and computers this didn't matter. Old TVs were very forgiving to this non standard video format. The processing was all done in analogue mode with no CPU telling you "no I don't understand that format". Old TVs would display something whatever you threw at them! Hard to describe or visualise if you've never seen an out of sync picture.
Although the HDMI standards do support a 288p (p for progressive) mode, it is not commonly implemented.
Users of old computers and consoles have looked for solutions to convert the old 8-bit video into modern HDMI format. At least in the UK all modern TVs cannot display the old style analogue RF signal output (from the modulator) as digital TV now uses a digital RF signal (bad explanation, but the RF signal standard changed with the introduction of digital TV). Rooftop aerials are still very very commonly used in the UK to pick up RF digital signals.
To convert from old 8-bit video in the non standard 288p format to a corresponding HDMI format is not so easy, and gets ever nastier if you have to convert from 50Hz to 60Hz. There are various modules to do this, but their ability to understand 288p varies and the output HDMI picture quality is not ideal. There are more specialised converters (they use FPGAs of course) but these are expensive. I am trying to roll my own.