Palcom Laserdisc: how does it work?

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Door nitrofurano

Champion (287)

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27-01-2014, 19:09

since i'm interested on developing homebrew stuff (even experimental) for hardware like Palcom Laserdisk, and after trying to read OpenMSX sources related to it at http://sourceforge.net/p/openmsx/openmsx/ci/master/tree/src/... and http://sourceforge.net/p/openmsx/openmsx/ci/master/tree/src/... , i have some questions like:
- which connections and/or i/o ports are used?
- how far can we hack dvd-players to behave exactly like Palcom Laserdisk, when they are connected to a MSX? (i guess it is possible somehow?)
- what do we need to have in mind when attempting developing?
- are there more people here in this forum also curious about homebrew development on this kind of hardware? and which kind of ideas would be great seeing there? (i guess that even games (or whatever) based on wild demoscene production videos found at Pouet could be interesting )

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Van enribar

Paladin (1004)

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27-01-2014, 19:33

my idea is: build a universal remote control to connect to the MSX (via a cartrige, via the joystick port, via the printer port, etc.) and connect DVD player to a MSX with superimpose capabilities. After that, create a MSX-Basic extension with new CALL commands to manage play, pause, stop, next chapter, etc.
I think this is the cheapest solution to have a modern laserdisk like system! :-)

Van bakoulis

Master (166)

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27-01-2014, 19:42

enribar wrote:

my idea is: build a universal remote control to connect to the MSX (via a cartrige, via the joystick port, via the printer port, etc.) and connect DVD player to a MSX with superimpose capabilities. After that, create a MSX-Basic extension with new CALL commands to manage play, pause, stop, next chapter, etc.
I think this is the cheapest solution to have a modern laserdisk like system! :-)

I am interested for that too. How exactly can will do that?
Smile

Van Metalion

Paladin (1013)

afbeelding van Metalion

27-01-2014, 20:35

Nitrofurano,

Some DVD players are equipped with a RS-232 connector. For most, that RS-232 connector is used for servicing the player, but in some cases, they accept a certain level of commands.

Take an MSX with a RS-232 connector, find a DVD player with a RS-232 connector too, and if you know the bytes needed to send a command, you're in business ...

Running Naked in a Field of Flowers

Van seanyoung

Resident (53)

afbeelding van seanyoung

27-01-2014, 20:37

The laserdisc is controlled with the NEC IR protocol, but over a wire rather than with infrared light. There are three wires in the control cable:
1) NEC IR (from MSX to laserdisc) to send commands like remote control key presses
2) ACK (from laserdisc to MSX) to confirm command and completion

So when the MSX sends PLAY to the laserdisc, ACK is held low while the disc spins up etc. It goes back up once the disc is playing.

There are only a few pioneer laserdisc with the right interface. If you want to use a DVD player then you'll need to find one with a suitable interface.

Van seanyoung

Resident (53)

afbeelding van seanyoung

27-01-2014, 20:42

Ah I forget, there is also an EXTINT which from the laserdisc to the MSX. When the laserdisc will stop playing it signals this. When the laserdisc stops the MSX will stop superimposing before it loses v-sync

Van Manuel

Ascended (15804)

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27-01-2014, 22:06

What about the key thing of laserdisc: you can ask it to play certain frames... but that concept doesn't exist on DVD players, does it?

Van mars2000you

Enlighted (5515)

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27-01-2014, 22:38

On DVD's, you have titles and chapters. So, you can play directly some parts and you can also go directly to a specific time (you can check that in VLC).

Van enribar

Paladin (1004)

afbeelding van enribar

27-01-2014, 22:43

listen to me :-) dvd players are cheap and everywhere around you, also blu-rays can read dvds, but not all these players have rs-232... So... what the sense of this big effort to connect msx via rs-232? you can find easely universal remote controls and I think it is quite easy to manage them from the msx.

Van seanyoung

Resident (53)

afbeelding van seanyoung

27-01-2014, 22:52

With a "universal remote" you won't know when the DVD player starts playing. The laserdisc player provides the ACK connection for this; you won't this have with with pure infrared.
Note that it takes a non-determinstic amount of time to spin up or seek on optical media.

On the other hand you could easily make an IR transmitter from the MSX using the printer port and an infrared led. You'll have to hand code the z80 code by the cycle but this is not too hard.

But still you won't succeed

Van mohai

Paladin (841)

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19-07-2019, 17:50

I am sorry to resurrect this thread now.

There are some wrong ideas about Laserdiscs and MSX.

I have been experimenting with a European Palcom PX-7 and a semi-compatible player (and, of course, some LD games).
It is not true that there is only one model suitable to play games. There are a few compatible (you can read about the different models in the game sleeve itself) and some do not connect to the Din-8 connector, but instead, to a simple mini-jack mono.
This means no /ACK signal from the player so, how does the game knows when the player is playing or not?
Well, there is an internal signal in the Palcom that activates when external video is detected. I guess this signal is read by the game,
after issuing a command and the image/video is shown.
In real LD players, after a "play" or a "jump to frame" command is issued, player shows black screen (no video) for a while, then the image.
This serves to the MSX to detect when the required image/video is shown, after issuing a command.

DIN connector is suitable for models such as LD-700 (and compatibles) and mini-jack connector is for models like LD-1100.

Both connectors output the IR commands for the player but are electrically different so, if you want to connect your player to it, you will have to find out which connector is electrically compatible with yours.

Another issue is the command set used. The one for LD-700 is different from the one for LD-1100.

I am using a modded CLD-1450 player (can play both NTSC and PAL discs and can output NTSC or PAL).

I found out that this player is command-compatible with LD-700 and the compatible connector is the DIN-8, but my player has only mini-jack mono connector on it.
So, I did a cable from the DIN connector to the mono jack and was able to control the player from P-BASIC.

The problem is that, when I load a game, the disc starts to play, the game loads and starts but the player does not stop and the selected image (or video) is not shown.
The video goes on and on ...

This shows that there are many players compatible to play games. I think that most modern players use the same command set as the LD-700, but lack of a /ACK signal (at least, not an external /ACK signal. Maybe an internal compatible signal?)

I think the problem now is that my player is not activating /ACK signal, but is accepting LD-700 commands, so the game thinks that the player is not an LD-700, as the /ACK signal is not activated
and, maybe, after the game loads, it sends LD-1100 type commands because it does not detects /ACK active.

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