Re: [sebhc] TMS9918 on the H8 bus .... alive and well³

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terry.smedley

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Sep 15, 2021, 3:44:19 AM (8 days ago) Sep 15
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I looked at the OSSC scan converter in your link.  It doesnt support composite, but they do reference a unit by "RetroTink" that does.  I have a "2X mini" coming and will report the results.



Terry

Sent from my Verizon, Samsung Galaxy smartphone


-------- Original message --------
From: Glenn Roberts <glenn.f...@gmail.com>
Date: 9/15/21 12:22 AM (GMT-08:00)
Subject: Re: [sebhc] TMS9918 on the H8 bus .... alive and well

I have a small 9” Sony trinitron and a zenith color (ZVM-135?) crt . I will take pictures of both but I think the Samsung flat screen I’ve been using is probably the best quality of the three.

Sent from my iPad

On Sep 14, 2021, at 11:54 PM, terry.smedley <terry....@gmail.com> wrote:


Glenn:

The HA-8-3 does its wait states by counting clock cycles, so it's got the right timing only at 2MHz.  I was hoping you'd be able to eek 4 out of it.  

Small consolation, but the clone will not have that limitation.

FWIW, I see there is quite a market demand for old analog monitors by "classic gamers" who are trying to avoid all the digital artifacts associated with upscaling a composite video image to a HD display.  I believe you said you didn't recall the HA-8-3 looking any better on the Heath analog display.  A family member still has a Trinitron (!).  If I can get somebody to help me lift it into and out of my car, I will try to have a look at the HA-8-3 graphics on it.

Terry










Sent from my Verizon, Samsung Galaxy smartphone


-------- Original message --------
Date: 9/14/21 7:05 PM (GMT-08:00)
Subject: RE: [sebhc] TMS9918 on the H8 bus .... alive and well

When I try to increase the speed above 2Mhz the system just hangs.  I presume this is because of the presence of the HA-8-3 but there’s a simple way to test that – I’ll pull it out at some point to see if that’s the issue.  Too bad. These demos would look much nicer at higher speed.  Then again we are trying to demonstrate what life was like back in the 80s!

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of norberto.collado koyado.com
Sent: Tuesday, September 14, 2021 5:30 PM
To: se...@googlegroups.com
Subject: Re: [sebhc] TMS9918 on the H8 bus .... alive and well

 

HDOS Speed Application is here:

 

 

 

Let me know if any issues in case it is not the latest version.

 

Norberto

QSH89SBC Software Update (CPM BIOS with H17/H37 Support) - by Ken

 

 


From: se...@googlegroups.com <se...@googlegroups.com> on behalf of terry.smedley <terry....@gmail.com>
Sent: Tuesday, September 14, 2021 2:24 PM
To: se...@googlegroups.com <se...@googlegroups.com>
Subject: RE: [sebhc] TMS9918 on the H8 bus .... alive and well

 

Glenn:

 

I am away from home until Friday...but I'm sure someone can provide an HDOS link.  If you do from scratch, you'll need to write the changes to the shadow memory byte for the control port and the port will be updated at the next 2ms tick.

 

The HA-8-3 makes extensive use of wait states to meet timing constraints.  Unfortunately those wait states are based on counting bus clock cycles with shift registers so as the bus speed goes up, the delay goes down and will likely fail at higher speeds.  An HA-8-3 clone will use fixed timing waits that are independent of bus or CPU clock and higher speeds will be possible.  When running the experimental board without revised wait state circuitry, I could run video at 16MHz without crashing, but at any speed above 4MHz there were obvious display problems.  Let us know how far you are able to push the HA-8-3.

 

Terry

 

Sent from my Verizon, Samsung Galaxy smartphone

 

 

-------- Original message --------

Date: 9/14/21 2:10 PM (GMT-08:00)

Subject: RE: [sebhc] TMS9918 on the H8 bus .... alive and well

 

Getting some interesting graphics demos from the Lucidata pascal package

https://photos.app.goo.gl/HHpA6eqJguRfrtjB9

https://photos.app.goo.gl/FvdR3a5XqdV6eoAx9

 

pretty nice implementation.  good resolution and quality.

 

I don’t think I used it much back then as all I had was a dual (100K) floppy system.

 

Compiling and running at 2Mhz sure seems slow though!...

 

Is there an HDOS version of SPDSBC out there somewhere that I can grab?  This is for the Rev 3.1 CPU board.  If not I suppose I can create one from Douglas’ CP/M version…

 

Also do we know how fast we can push the HA-8-3 in terms of CPU speed?  I guess I’ll find out soon enough…

 

  • Glenn

 

 

From: glenn.f...@gmail.com <glenn.f...@gmail.com>
Sent: Tuesday, September 14, 2021 6:33 AM
To: se...@googlegroups.com
Subject: RE: [sebhc] TMS9918 on the H8 bus .... alive and well

 

Thanks Terry. I applied the patch

https://photos.app.goo.gl/x81KA4RSvrqGDQUZ7

 

not sure this makes much of a discernable difference.  The main application that stresses the video is the MUSICK (kaleidoscope) program.  As I watch the kaleidoscope change on the screen it will go from an image that looks quite good to one that shows a lot of ringing simply based on the change of only a few cells. Perhaps the pattern at the edges determines the “ringing” for the whole image?

 

My recollection is that this was always a challenging graphic.  For my purposes I’m good with what we’ve got.  Will focus on having a few games and demos to show.

 

back in the 80s I was interested in high level language bindings for the HA-8-3.  I have a copy of Lucidata Pascal, which had full support.  It produces pseudocode which must be run with a PRUN executive.  I’ll take a look at that and see if they had any interesting demos on that disk.

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Terry Smedley
Sent: Tuesday, September 14, 2021 1:38 AM
To: SEBHC <se...@googlegroups.com>
Subject: Re: [sebhc] TMS9918 on the H8 bus .... alive and well

 

Glenn:

 

I found a couple of tweaks that seemed to help the edge ringing.

 

The TMS9918 has an "External Video" input that is mixed with the internally generated video to produce the composite output.  That external input isn't used, and on the clone and I believe the HA-8-3 that pin is simply left unconnected.  I found an observable and reproducible improvement in video quality by grounding that external video input.  It is pin 35 on the TMS9918 (adjacent to the composite output at pin 36).  You might try jumpering pin 35 to ground and see if you see similar improvement.

 

With that improvement, what I observed is that edges now appeared "soft" or "smeared", rather than "ringy".  I had previously turned the monitor sharpness all the way down to try and relive the ringing edges.  Since I was now observing soft edges, I returne the monitor's sharpness adjustment to midrange.  The soft edges got considerably sharper, but with much less ringing that I had previously observed.

 

Finally, I saw in the TMS9918 datasheet a recommended interface to a video monitor that used no external components except for a 1K pull-down resistor.  Using patch cables that are ridiculously long given the frequencies of the video signal, I bypassed the external video amplifier transistor and routed the video signal straight from pin 36 of the TMS9918 to the monitor, with the 1K pull-down resistor (to ground).  I believe that improved things, but I can't gauge that for certain until I can patch the circuit board properly.

 

All of this is to say that I think there are some improvements possible by tweaking the video amplifier circuitry (Q1 through Q4 on the HA-8-3). What I know about high frequency amplifiers would only partially fill a very small thimble, so if there are any video experts out there who can look at the HA-8-3 schematic and offer suggestions - I'm all ears!  I'm looking for the ColecoVision schematic to see what was done on that high-volume commercial design.  

 

Terry

 

On Monday, September 13, 2021 at 6:52:15 PM UTC-7 Glenn wrote:

The board has a 3-pin header that outputs the composite signal. It came with a coax cable that has a 3-pin Molex on one end and an RCA jack on the other. I simply plugged the RCA jack into the composite input on a Samsung LED tv.

To Terry's question: I have run this card using the old Zenith color monitor. My recollection is it's not much better.

I wonder if a better cable would help? impedance issue?

-----Original Message-----
From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Dave McGuire
Sent: Monday, September 13, 2021 9:48 PM
To: se...@googlegroups.com
Subject: Re: [sebhc] TMS9918 on the H8 bus .... alive and well


It really does look like ringing. If the sharpness is increased, there will be a faster rise time on the waveform, resulting in more ringing. But something is causing those reflections in the first place.

I've seen this in the past using NTSC video monitors that had switchable 75-ohm termination on their inputs, and the termination was disabled. A 75-ohm driver sending fast edges into a high-impedance receiver will certainly do this, due to the impedance mismatch.

-Dave

On 9/13/21 9:42 PM, Terry Smedley wrote:
> The images I see with the clone have the same edge artifacting that
> Glenn noted. Has anyone looked at this on a vintage analog display?
> Some of the edge artifacts look like they could be due to sharpening
> after upscaling to a digital display. I experimented a bit by turning
> down the sharpness on the monitor, and at least when viewed from a few
> feet away, the picture looks better to me. Instead of the edge
> ringing, there's a smoother transition which is easier on my eye. But
> razor sharp, it's not.
>
> Terry
>
> On Monday, September 13, 2021 at 6:23:29 PM UTC-7
> mcg...@neurotica.com
> wrote:
>
> On 9/13/21 8:36 PM, glenn.f...@gmail.com wrote:
> > Led: I see what you mean. Maybe I’m too close to the screen (or I
> should
> > take off my glasses!). I’ve added some pix to my vcf album
> (scroll down…)
> >
> > https://photos.app.goo.gl/Bqqr9Cn1ohJaCPyC7
> <https://photos.app.goo.gl/Bqqr9Cn1ohJaCPyC7>
> > <https://photos.app.goo.gl/Bqqr9Cn1ohJaCPyC7
> <https://photos.app.goo.gl/Bqqr9Cn1ohJaCPyC7>>
> >
> > the flag and the globe look great. The kaleidoscope shows a lot of
> > issues at the rectangle boundaries. Is this about what you’re
> seeing?
>
> Those "echoes" surrounding vertical lines sure look like reflections
> on an unterminated transmission line. How are you feeding the video
> into the monitor?
>
> -Dave
>
> --
> Dave McGuire, AK4HZ
> New Kensington, PA
>
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Dave McGuire, AK4HZ
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