Pentranic CGA Monitor. Custom CRT_Range. GroovyArcade.

[lettuce]

Hi am after some pointers in defining a custom crt_range for my Pentranic 15khz monitor. Below is some tech on the monitor:

DY Parameter     
26", 28"     LH=1.33mH 
LV=18mH    RH=1.50
RV=5.65
29", 34", 38"      LH=0.96mH
LV=17.6mH    RH=1.1
RV=5.6
<1> SPECIFICATIONS:
      1. CRT size: 26", 28", 29", 34", 38"(diagonal measure)
      2. Phosphor type: P22
      3. CRT etch: Polished faceplate: other faceplates available
      4. Striped trio spacing: 0.84mm(26", 28", 29"), 0.89mm(34", 38")
<2> INPUT SIGNALS:
      1. Input connector: 0.156 center header
      2. Video type: RGB analog
      3. Video input impedance: 1K Ohm; other values available
      4. Video level: 1.5 to 4 vlots peak-to-peak; other levels optional
      5. Sync type: TTL sync; separate or composite, negative or positive
      6. Sync input impedance: 4.7 Ohms
      7. Horizontal sync frequency: 15K(CGA)
      8. Vertical sync frequency: 47 to 63 Hz
<3> GEOMETRY:
      1. Horizontal linearity: 5%
      2. Vertical linearity: 5%
      3. Picture size regulation: 2%
      4. Geometric distortion: 2% max
<4> POWER INPUT:
      1. Input voltage: 96~240VAC, 50~70Hz; no isolation transformer required
      2. Maximum power: 120 Watts
<5> USER CONTROLS:
      1. Remote controls:     Brightness, contrast, horizontal size, horizontal centering,
horizontal frequency, vertical size, vertical centering, vertical frequency.
      2. Internal controls: Focus, Screen, Vertical linear, B+
<6> RESOLUTION:
      1. Graphics modes: Standard Res - 640x200(may be limited by the CRT)
      2. Video bandwidth: 15 MHZ typical

The display im getting in GroovyArcade seem to be real good atm but one thing i have noticed is that i have the Vertical Shift pot cranked up all the way on the control board for the monitor but there is still about a 1/2 inch black boarder at the very top of the screen, so i want to see if i can shift the whole screen up a fair bit, ideally so i can turn the V Shift pot down to about half way and have the screen sitting in the middle of the monitor, that way gives be alot of play with the pot either way.

Im not sure how i even go about this in GroovyArcade's GRUB menu though??

[Calamity]

What monitor preset are you using in the monitor setup, arcade_15?

[lettuce]

Yeah, Arcade 15.7kHz - Standard Res

[Calamity]

You have to edit mame.ini (setup menu, sytem setup, mame manual settings):

monitor custom
crt_range0    15625-16200, 49.50-65.00, 2.000, 4.700, 8.000, 0.064, 0.192, 1.024, 0, 0, 192, 288, 448, 576

This is equivalent to arcade_15. No decrease the vertical back porch (remarked value), by steps of 0.064: 0.960, 0.896, etc.

In theory, this will push the picture up.

[lettuce]

So try,

 crt_range0    15625-16200, 49.50-65.00, 2.000, 4.700, 8.000, 0.064, 0.192, 0.896, 0, 0, 192, 288, 448, 576

as a starting point

[Calamity]

Yes, that should make a visible change.

[eboshidori]

<6> RESOLUTION:
      1. Graphics modes: Standard Res - 640x200(may be limited by the CRT)
      2. Video bandwidth: 15 MHZ typical

The video bandwidth is the most important parameter, because that's the limit of the pixel clock you can send to the monitor. Manufacturers define some typical settings (ex: 640x200, 47-63 Hz) , but they don't reflect the whole range of what the screen can actually accept.
One guy here has a tri-sync monitor that is supposed to support 90 Hz max for vertical refresh rate, but he has sent a 120 Hz signal (31 kHz Hfreq). That's possible because his monitor's bandwidth is huge, and the signal was within the range of the components of the chassis, not of those indicated by the manufacturer.

So, instead of looking for that, we should take note of the bandwith. Every monitor has components that can supply the power to move the beam all across the screen, but the ability of changing the spot size between different states (according to the different pixels of the signal) is limited by the bandwidth. A monitor with a 15 MHz bandwidth can't display the pixels of a VGA signal, because the pixel clock of such signal is above 15 MHz for the pixel clock (typicaly : 25.2 MHz). The factor here is the switching ability (the delay between two states). If you send a 31 kHz signal to a 15 kHz screen, you will see a picture, but unusable because the components aren't fast enough. When considering a compatible signal, you have much wider range of possibilities than those specified by manufacturers.

Same goes for a PAL TV for example, which is supposed to work around a 15625 Hz, but can accept timings that are way outside. The guys who connect arcade boards on TVs (with SuperGuns) don't have much trouble, and many arcade systems send signals below 15625 Hz (not the "typical" 15.7 Khz). For example, the PGM sent a ~ 15150 Hz signal, and since it came out no monitors had any trouble to display the picture, whether in arcades or later at home.
Considering that PAL TVs work with a xtal that is 4 time the color subcarrier (4.43 x4 = 17.72 MHz ), that means we can have the same bandwidth if the video amplifier follows.

So, the different monitors presets indicated for GroovyMame tend to be pretty narrow. That means modelines generated with pixel clocks above MAME specifications, and the risk of not matching the exact frame duration. For example, the CPS-III pixel clock is 7.5 MHz (Hfreq = 15432 Hz), but when you have 15450 Hz as the lowest Hfreq in preset, that means you must go for a higher pixel clock, and higher numbers for pixels/lines. Since we deal with integers numbers and a granularity of 0.01 MHz for pixel clocks, there's no chances to get a signal that matches MAME frame duration. It could be close, but not enough to avoid using triple buffering...

CRT chassis are much more flexible, and digitals one (since 1994) aren't has vulnerable to out-of-range timings than the old analog ones (from the 80's). Users should do some tests to really check what are the lowest and highest frequencies that their monitors/TVs can accept.

[lettuce]

I tried,

crt_range0    15625-16200, 49.50-65.00, 2.000, 4.700, 8.000, 0.064, 0.192, 0.896, 0, 0, 192, 288, 448, 576

and

crt_range0    15625-16200, 49.50-65.00, 2.000, 4.700, 8.000, 0.064, 0.192, 0.064, 0, 0, 192, 288, 448, 576

an neither seemed to move the display up any further at all??

Eboshidori, do you suggest something else then?? As i think ive move the picture up as far as i can in regards to using the control board of the monitor, i can move the display down vertically loads, just doesnt seem to be much room for moving the display up!?

[Calamity]

Try lowering hfreqmin from 15625 to 15250.

[lettuce]

Try lowering hfreqmin from 15625 to 15250.

Shall i change the vertical back porch value back to 1.024??

[eboshidori]

In CRT display, moving the picture down or to the right means adding little delay to the signal. And you can't add much delay, neither you can go faster than the signal (that would mean negative delay ), so when you cant' move your picture any higher on the screen, that means you have reached the zero delay point. You need to work on the signal itself, ie having a longer back porch duration, because the back porch is in the first position on top of the screen, before the active display (picture ends with front porch, at bottom).

If the duration of 0.896 ms is not enough, then the parameters with 0.064 won't do better. You need more than that.
But anyway, these parameters are defined for a line duration of 64 µs,  and while some arcade boards do display lines of that duration, they don't necessarily display 262 lines per frame... Ex: the Neo Geo signal is 15625 Hz, so 64 µs for the line duration, but you have 264 lines instead of the expected 262 lines for 240p stuff. So even if you have 14 lines for the back porch (0.896 ms) in your parameters, you'll have a picture that is sligthy off centered.
The Neo Geo signal has 8 lines for the Vsync (0.512 ms, not 0.192), and 16 lines for back porch (not 14). So for the centering, you got 24 lines for the real board (8+16) VS 17 lines for the emulated part.

There are other cases when you have 224 active lines like Neo Geo or many other systems, but only 256 total lines (the PGM), or 259 (Capcom ones, like the 3 CPS and others). So at the end, specify durations for all that stuff doesn't mean it will perfectly fit for every case (in fact, for very few).

What I suggest is to only focus on centering the picture, ie that the middle of the active display matches the middle of the active display of the NTSC standard, because this standard is followed for TV screen as well as arcade monitors. You have some variations for the overscan, but the rest is pretty close.

So, first you adjust the geometry of your screen (arcade or TV) according to the NTSC standard, and then you adjust modelines (or modeline generation) to follow that standard (instead of values indicated by manufacturers, who can be wrong), meaning at the end you just have to slightly modify the size of the picture (Hsize + Vsize, that affects the amplification value for driving the yoke), and you don't care anymore of centering the picture.

If we specify lower frequencies for monitor presets, there's more chance to matche what comes from the real hardwares and MAME timings (when they are correctly written...), and if we follow the same geometry setting for our screens (once for quite), then everything would be identical for everyone. The limit is the size of the different pictures, because it's impossible to have the exact same size for every stuffs, since arcade boards have different pixel clocks and different total frame sizes (that we must follow to have the same frame duration). But everything is supposed to be within the active display of the NTSC standard (or very close to), and according 5 to 10 % overscan in mind.

[Calamity]

Shall i change the vertical back porch value back to 1.024??

Yes. After that you can combine both things, 15250 and decreasing the back porch, probably both things are required. 15250 might be too low actually, if that's the case try moving the hfreqmin value in the 15250-15625 range.

[lettuce]

Ok i have tried a number of combinations between the hfreqmin and vertical back porch and it does seem to shift the display up at all, not enough to notice. I was really hoping this was going to shift the image up about an inch or so

[Calamity]

In CRT display, moving the picture down or to the right means adding little delay to the signal. And you can't add much delay, neither you can go faster than the signal (that would mean negative delay ), so when you cant' move your picture any higher on the screen, that means you have reached the zero delay point. You need to work on the signal itself, ie having a longer back porch duration, because the back porch is in the first position on top of the screen, before the active display (picture ends with front porch, at bottom).

The key to have all video modes vertically centered is to find the actual retrace time of your particular CRT. The way to find it is by experimentation.

The sync pulse + the vertical back porch of a modeline needs to be at least as long as the retrace time of the monitor so you don't have issues of compression or missing lines at the top the screen, or even visible return diagonals.

But if the vertical back porch is too long, then the extra lines are accumulated forming a black border on the top of the screen.

As we need to add padding lines to keep 224p and such resolutions within the 15.625 working range, knowing the *exact* retrace time allows GroovyMAME to decide which ones of total required lines correspond to retrace and which ones are mere padding, so it will divide the same amount of padding lines between the front and back porches, thus making all possible resolutions be perfectly centered on the vertical.

Unfortunately no one is actually measuring his monitor's retrace time, as far as I know, even if I've explained the process in several threads.
 

[Calamity]

Ok i have tried a number of combinations between the hfreqmin and vertical back porch and it does seem to shift the display up at all, not enough to notice. I was really hoping this was going to shift the image up about an inch or so

That's odd, do you really see any change at all?

Did you set the monitor type as 'custom'?

Have you tried that monitor with a different source, Windows, pcb, etc?

[lettuce]

That's odd, do you really see any change at all?

Did you set the monitor type as 'custom'?

Have you tried that monitor with a different source, Windows, pcb, etc?

Ah cack, its still as Arcade 15khz i believe, so just change that to custom yeah?

Have notice a few Vertical games, dont display well at all, all the screen is broken up like its out of sync, Truxton and Truxton 2 spring to mind

[Calamity]

Ah cack, its still as Arcade 15khz i believe, so just change that to custom yeah?

Also make sure you don't leave by accident a duplicated crt_range0 option in mame.ini set as 'auto'.

Have notice a few Vertical games, dont display well at all, all the screen is broken up like its out of sync, Truxton and Truxton 2 spring to mind

That's due to the hfreqmax value: either lower this one or tweak the hfreq pot on the chassis.

[lettuce]

That's due to the hfreqmax value: either lower this one or tweak the hfreq pot on the chassis.

Altering the pot on the chassis isnt really an option as in doing so cause the lettering on Advmamemenu to become blurry and not sharp

[eboshidori]

Ok i have tried a number of combinations between the hfreqmin and vertical back porch and it does seem to shift the display up at all, not enough to notice. I was really hoping this was going to shift the image up about an inch or so

I forgot to mention, but you can't change only the back porch value, but the front porch as well (if not, you change the total number of lines). For the same number of total lines, you have the Vsync lines and the active display lines that remain the same, the other lines are the porches. So you have a distribution between back and front, knowing that normally the back porch is always much longer than the front porch. For a 262 lines signal, you typically have 3 lines for sync, 16 lines for back porch, 240 active lines (224 visible because of overscan), and 3 lines for front porch. To shift your picture, you either do it on your monitor (adding delay), or you modify the signal. The example I wrote was about shifting the image down, but to shift up, you modify the same things (back and front porch distribution).

[lettuce]

Ok setting,

crt_range0    15625-16200, 49.50-65.00, 2.000, 4.700, 8.000, 0.064, 0.192, 0.064, 0, 0, 192, 288, 448, 576

seem to set be the ideal setting for the monitor, have the v position pot set in the middle and the display is in the middle of the screen

Now regarding the vertical games, in this case truxton, i have lowered the hfreqmax value to


crt_range0    15625-15950, 49.50-65.00, 2.000, 4.700, 8.000, 0.064, 0.192, 0.064, 0, 0, 192, 288, 448, 576

which gives me a display now but the top of the screen where the score is has 2 or 3 think black lines going across the screen

[Calamity]

which gives me a display now but the top of the screen where the score is has 2 or 3 think black lines going across the screen

Of course, 0.064 is ridiculously short for a vertical back porch, you need to increase that value until those retrace diagonals dissappear. Then you'll have found the retrace time of your monitor. Once then, you may increase the vertical *front* porch too to compensate for the shift (this will push the picture up), as Eboshidori pointed.

[lettuce]

Ok, the following seems to be a good point,

crt_range0    15625-15950, 49.50-65.00, 2.000, 4.700, 8.000, 0.896, 0.192, 0.896, 0, 0, 192, 288, 448, 576

Is there anything else i should try and lock down/fine tune??

[Calamity]

Now your front porch is huge! 0.896 is 14 lines, that's too much. I wouldn't put there more than 3-4 lines (0.192-0.256). Whatever that's enough to make the centering possible through the v-shift pot, even if you don't end up with the pot set in its middle position.

That big porch is possibly causing gunforce not running at 100%, due to the extra lines your adding.

[eboshidori]

Is there anything else i should try and lock down/fine tune??

Yes : your monitor setting !!!! 

At some point, you can't mess up anymore with signal, you HAVE to properly set up your picture position (ie : delay) on the monitor itself. You have to shif up the picture (reducing delay), and go back to normal values for back and front porch for modelines.


Few words about this :

In video signal, porches are set to 0.3 Volt. It's like "displaying black" from the point of view of the screen, because the visible picture is made from the 0.3-1 V part of the signal, and anything below 0.3 V is for the sync pulses (that's what you call "negative sync", because it's below the video part).
These porches have two purpose : adding time to restore DC current in older analog chassis, as well as providing enough time to move the beam from bottom to top. Back then, if you displayed a full white picture and then go directly to sync pulses, you got nasty artifacts. So, it was decided to add some lines to avoid this . But they aren't evenly distributed ! You have juste enough time at the end of active display (front porch), and the back porch takes into account the time to move the beam. That's why on regular 262 signal, you have just 3 lines for front porch, and 16 for back porch (16.5 for interlacing). Those specifications where made in a time when components of television where much slower than today.
In early days of NTSC, the vertical blanking interval was set to : 525/485 = ~8% of the total number of lines. When you look for the VESA specifications for PC monitor (which are much faster than broadcast stuffs), you generally see 5% for the Vblank, and often just one single line for front porch. That's enough for the end of the signal, but you still need enough time (lines) for back porch. If you decide to go bellow that duration, you'll reach the limits of the components and begin to see some artifacts.

[lettuce]

Ok, the following seems to be a good point,

crt_range0    15625-15950, 49.50-65.00, 2.000, 4.700, 8.000, 0.896, 0.192, 0.896, 0, 0, 192, 288, 448, 576

Is there anything else i should try and lock down/fine tune??

So do i really want to be locking down the HfreqMin-HfreqMax range as close to 15700 as possible then to match the 15.7khz range of the monitor??

[eboshidori]

crt_range0    15000-16500, 49.50-65.00, 2.000, 4.700, 8.000, 0.192, 0.192, 1.024, 0, 0, 192, 288, 448, 576

3 lines for front porch, 16 lines for back porch. And adjust the position on the screen !

The Hfreq range covers most of the arcade boards. If those boards were designed to output those frequencies, that's because arcade monitors could handle them (something which is more difficult for TV screens). So if you are using such a monitor, use the full possibilities.
With 15 MHz bandwidth, I suspect that you can go higher than 16500 Hz, but you need to test it.

[Calamity]

Well, considering the original problem was the v-shift control wasn't able to center the picture, I think he should keep the bare minimum retrace time he just found (0.896), assuming this value is right. Otherwise he would be adding extra lines to the top:

crt_range0    15625-15950, 49.50-65.00, 2.000, 4.700, 8.000, 0.192, 0.192, 0.896, 0, 0, 192, 288, 448, 576

Anyway, try both settings and report what's working better. Just bear in mind the hfreqmax shouldn't be greater than 15950, otherwise vertical games didn't sync properly.