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FarmerPotato

What would you do with dual screens on a 99/4A?

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Question: what video connectors would you care about?
  • DE-15HD (VGA) + jumper for RGB-Csync or VGA-Hsync-Vsync
  • SCART with jumper to choose RGB-S or composite
  • S-Video (basically free with CXA2075 encoder)
  • RCA composite (basically free with CXA2075 encoder)
  • 99/4A Din-5 composite
  • Commodore 1084S 6-pin DIN
  • Apple DB-15 RGB-S port (Apple IIgs, Mac era)
I consider SCART because some of us recommend Samsung 910MP with SCART.
I'm not sure what DE-15HD to SCART cable is available unless you wire your own.
I think Apple passive adaptors are generally available.
I think there should be a separate PCB for connectors, with a ribbon cable.
Pros: relieves stress, allows connectors to change without major rework.
Cons: impact on impedance, crosstalk

 

 

doesn't matter long as i can build a cable.. scart is preference for rgb/15

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SCART connectors are prohibitively large on boards. I also tire of building cables. I do prefer RGBc signals usually. I use an XRGBMini and a big SCART switch box.

 

There are suppliers of retro DIN to SCART cables. It'd be nice to be able to grab a pre-made Sega mega drive to SCART cable or something like that.

 

Then there are plenty of SCART/RGB to HDMI upscalers available.

 

I don't feel that 15khz VGA is very US common.

 

[email protected]

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SCART connectors are prohibitively large on boards. I also tire of building cables. I do prefer RGBc signals usually. I use an XRGBMini and a big SCART switch box.

 

There are suppliers of retro DIN to SCART cables. It'd be nice to be able to grab a pre-made Sega mega drive to SCART cable or something like that.

 

Then there are plenty of SCART/RGB to HDMI upscalers available.

 

I don't feel that 15khz VGA is very US common.

 

[email protected]

 

I looked up the Sega mega drive cable. I like that idea.

 

What I came up with was: put all the signals on a 2x6 header. Two of them for twin VDPs. Connect by ribbon cable to a small PCB with the port. So that could be a choice of two SCART, two VGA, or two Sega mini-DIN-8, all equally inexpensive from DirtyPCBs. For the EXT video source, I'm not sure what makes sense.

 

I'm not sure what RGBs sources you would be likely to have today? I imagine adding 99/4A graphics over your YouTube video production would be the typical use of an EXT source.

 

And how to record the combined result?

 

 

The more I look into it, the more I want to just have twin VDP with the ability to superimpose VDP2 over VDP1.

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This is a very interesting thread.

 

Guess cross-sharing ideas can't hurt; in the Colecovision section there is some VDP stuff being discussed and worked on as well:

 

 

https://atariage.com/forums/topic/291602-yet-another-80-column-expansion-idea/

 
 

 

 

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I've worked out most of the BOM and schematic for the twin 9958 option. No PCB layout yet. Parts ordered.

Features it does include:

  • Superimpose VDP1 over VDP2, or VDP2 over VDP1 on connector 1 only (simply set the Superimpose bit on one VDP, but never both.)
  • Mirror mode at startup
  • Independent VDPs after the first write to VDP2 only
  • 128K VRAM each.
  • RGBs, CV, SV out (Sony CXA2075 composite/SV encoder)
  • NTSC/PAL jumper
  • Choice of any 1 or 2 monitor jacks (twin 6x2 ribbon cables from board to jack PCB)
  • Single 9958 is an option by removing half the circuit.

Does NOT include:

  • External video input 
  • Extra 64K expansion VRAM
  • Fitting inside the console... maybe, maybe not. Uses 2x20 footprint to the 9918A socket plus 2 jumpers. I'm planning ribbon cable to external.
  • Convenient kit form.. uses surface mount but no smaller than 1206, 1.27mm, 1.78mm. I decided against AD1675-3 in 0.6mm TSSOP. The 1.27mm costs more $.

 

BUT this went down a priority level when my FORTI-2 PCB arrived. Too many projects!

 

I am also a big fan of the F18A and mk2. I anticipate making only about 10 of these Twin 9958.

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This is the superimpose switch:

         ________
YS1* ---|Set     |
Vcc-----|D      Q|________
YS2* ---|Reset   |        !
        |________|        !
       JK flip flop       !
                     _____!__
YS1* ---------------|A   sw  |
                    |       Y|__
!YS2*---------------|B       |  !
                    |________|  !
                  analog switch !
                                !
                           _____!__
RGB1 --------------------1|\   sw  |
                          | > --RGB|------ RGB
RGB2 --------------------0|/       |
                          |________|
                        fast RGB switch

VDP1 outputs YS1*, RGB1 (R,G,B)
VDP2 outputs YS2*, RGB2 (R,G,B)
VDP1 and VDP2 are synchronized (not shown)

 

When a superimpose bit is active, YS1* or YS2* emit 0s for transparent pixels. The first one to emit 0, flips Q to its side.


If YS1* flips Q to 1 (the default on powerup), the analog switch passes YS1*. If YS2* flips Q to 0, the analog switch passes !YS2*.

 

The fast RGB switch normally passes RGB1. When Q=1 and YS1*=0, it passes RGB2. That is, transparent pixels on VDP1 result in VDP2 showing through. If Q=0, the situation is reversed. The switch passes RGB2, but transparent pixels on VDP2 cause the switch to pass RGB1.

 

This circuit minimizes the parts cost: there is only one expensive (350MHz) RGB switch (AD1675-1 x3). It minimizes skew: VDP1 over VDP2 is the direct path. But VDP2 over VDP1 may have a slight skew from the NOT function of !YS2* which may blur the pixel transition a bit.

 

It's undefined what happens if both VDP1 and VDP2 have the superimpose bit set. They would constantly fight for Q, which is not a fast switcher; neither is Y. The output could be deeply weird.

 

What use cases does this support?

 

1. VDP2 over VDP1 would let you put titles onto VDP2, then run a normal 99/4A program (that is unaware of the Twin 9958) on VDP1 under the titles.

2. VDP1 over VDP2 would naturally be a way to get another scrolling plane, extra colors or deep background sprites.

 

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Searching for RGBs to VGA converter solutions I might include:

 

The GBS8200 is popular and not too much money. It's an external box.

 

The OSSC is a kit form with open source firmware. It uses an Altera FPGA, and some fancy video parts from TI, and a HDMI transmitter.

 

         
 
       
         
This is some really hard to solder stuff.
       
Designation Manuf. Code     Supplier URL
         
PCM1862 PCM1862DBTR TI Audio A/D Converter ICs 3.70
IT6613 IT6613E HDMI transmitter 3.8
Found on Aliexpress etc.
S25FL216K IS25LP016D-JBLE NOR Flash 16 Mbit 0.92
EP4CE15E22 EP4CE15E22C8N Altera Cyclone IV E 23.14
TVP7002PZP TVP7002PZP Video Digitizer 7.82
SN74LVC2G17 SN74LVC2G17DBVR Buffer 0.43
THS7353 THS7353PWR TI Video Amplifiers 3-Channel Low Power Video 4.15
         
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On 5/27/2019 at 1:10 PM, jedimatt42 said:

In MSX land, there is the V9990 Powergraph series of expansions, that is a second VDP on a card. The original version from the late 80s supported the graphics overlay mode so the output from the internal / builtin VDP can be fed as input into the second VDP. This allowed convential use as 1 screen...

 

The 2 VDPs are mapped into memory at different addresses ( well, those are Z80 systems, so different io-ports ) -- so a program can instruct them independently.

 

Today, the reproduction V9990's don't have the video input / overlay feature, so it gets you into a dual screen situation...

 

What would I be interested in doing with a second screen?

 

With 2 screens I can write games that put the status and score and player inventory or whatever on one screen, and keep the second 'immersive' ---

or... there could be online gameplay with room for 'party' chat on the second screen.

or... If overlay was supported, I could see writing some video titling for the second screen, that left controls and status up on the native screen so you don't have to memorize hot-keys... Even without overlay mode ( using post processing in a digital environment ) it could be usable. I've day dreamed about using the actual 4A to produce overlays for future youtube videos.

and... I would send debugging information to the second screen when developing on hardware.

 

[email protected]

 

 

I came back to this topic when I searched for V9990 info. 

 

By "reproduction V9990" do you mean the new carts? I read about original GFX 9000 that used a V9990 in the 90s. Now I see videos like this PowerGraph for MSX Turbo R which the poster says can only use a second monitor. They seem to have been made in small batches over the years as clones.

 

 

Or did you mean there is a reproduction chip? I hope not, that sounds sketchy.

 

I'm looking at the possibility of overlaying V9990 behind V9958, because V9958 has all the text modes and backwards compatibility, and V9990 has only new graphics modes. (including super fast font glyph copying, and unique Kanji ROM support, but still not text mode!)

 

The only lead I have right now on V9990 is 50 pcs @ $24 each . The VRAM like MT42C4256Z  turned out to be obtainable for a few bucks. (Aside: I had never seen a Z package. It is an idea that was made for routing PCB grids of memory chips.)

 

 

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i haven't really devoted the time to the technical aspects of the 994A architecture, but wow, there are some great discussions.  i can give some pie-in-the-sky-not-feasible use cases, though!

 

at a super high level, I think it would be really cool to use two screens for coding Assembly or Extended Basic (one for code, one for debug), or using Disk Manager to catalog then a copy a disk at the same time.  not sure on gaming applications- unless I was using one screen for taking notes in Adventure or Tunnels of Doom and the other to play the game.

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On 12/20/2019 at 9:30 AM, FarmerPotato said:

By "reproduction V9990" do you mean the new carts? I read about original GFX 9000 that used a V9990 in the 90s. Now I see videos like this PowerGraph for MSX Turbo R which the poster says can only use a second monitor. They seem to have been made in small batches over the years as clones.

 

Or did you mean there is a reproduction chip? I hope not, that sounds sketchy.

...

 

I was referring to the new carts. They all seem to leave out the video pass through/overlay/whatever it was of the original carts.   But I wasn't suggesting use of a Yamaha V9990 chip. If I recall, I was just suggesting the overlay technology would be nice option for a second VDP. For screens composed of 9918 plus 9938 

 

[email protected]

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Many of us are currently using the equipment to do 'sort of' a dual screen system.  It would probably be declared heresy by some, and I have serious doubts the developer would even entertain the merging, let alone have the time to spend on it.

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On 12/25/2019 at 9:10 AM, jedimatt42 said:

 

I was referring to the new carts. They all seem to leave out the video pass through/overlay/whatever it was of the original carts.   But I wasn't suggesting use of a Yamaha V9990 chip. If I recall, I was just suggesting the overlay technology would be nice option for a second VDP. For screens composed of 9918 plus 9938 

 

[email protected]

The 9918 though has composite video in, which means you need an external genlock and 9938 composite out.

 

The Superimpose function on the 9938/9958/9990 is set up for the family to work together. You use an external RGB switch controlled digitally. I think that I build the circuit from p104 in the 9938 manual to genlock two of them. 

 

It seems easier to start with two 9938/58 than to use the 9918A video in. I guess 9918/9938 would use the same genlock circuit though with an LM1881 sync splitter. Interesting.

 

I think I read that to superimpose 9958/9990, the V9990 must be run at the same horizontal dot rate. But if I read the the V9990 manual right, the incompatible modes are the 14.3 MHz external clock, overscan "panel" mode (for advertising or pachinko?), and the VGA mode (25.2 MHz clock in, 31.5kHz 640x480 out.)

 

So I don't know the  reason yet why the MSX Turbo R carts moved away from superimpose. Sure it's easier to build. I haven't come out of lurking on MSX forums to ask questions (and many of the threads are from 2007...)

 

Today I'm building  a plain 9958 prototype. Doing the research was fun, but it's time to build some stuff.

 

 

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If you replace the 9918 with the 9928, you get that same concept of external video mixing (though you need to deal with the component video out ;) ). I have tried one in a 4A console and it runs fine.

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A few years ago, I made two dual VDP prototypes boards for Apple II, based with two TMS9929A (master and slave), I planned to do the same for the 99/4A but I had never found free time for that project.
My v2 board is working as  on the arcade Pinball machine with vidiot "Granny and the Gators" 

You'll find the theory of operation and the schematics here: https://www.ipdb.org/machine.cgi?id=1083

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