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PlayCable research and development

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This thread gathers together technical information about the Intellivision PlayCable service and summarises it in the following document:

 

playCableTechnicalSummary-20190918.pdf

 

Please let me know of any corrections or additions you think should be made. The most recent version of this document will always be found here, at the top of thread.

The following video shows roughly what the PlayCable was like to use, based on a PlayCable Phoenix replica that has been put together:

 

 


If you want to try out the replica menu system for yourself you can use the following ROM image in JzIntv:

 

 

post-46336-0-10395800-1546328324.png post-46336-0-23791600-1546341026.png
 

 

Note that this does not contain any game ROMs and while it will fake the PlayCable loading each game, unlike the PlayCable Phoenix board itself, no games are actually payable.

Additionally, the following ROM contains the unadvertised stream #8 from the final menu page. This contains the credits for the PlayCable menu program, accompanied by Bach's Prelude and Fuge #6:

post-46336-0-03710400-1546328292.png post-46336-0-66189000-1546328292.png
 

 

Finally, to make sense of the first page or so of this thread it is probably necessary to know that this posting originally contained the following teaser:

 

Q. How much RAM does a PlayCable contain?

 

 

A. 8K x 10bits ;)

Edited by decle
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That's awesome. I think The playcable has five 16kbit ram chips. I figure after it first downloads the menu system (and music) that leaves at least 6k (maybe more) for downloading the game. Locomotion uses close to all of the 8k rom and would not have been compatible. Playcable might have been cancelled by then anyway. Had they built the menu system in rom they should have got all 8k out of it. I like how it lights up the colour bars. Maybe one bar for each K loaded.

 

That red thing you're plugged into, is that a chip socket? Was it originally empty?

Edited by mr_me

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That's awesome. I think The playcable has five 16kbit ram chips. I figure after it first downloads the menu system (and music) that leaves at least 6k (maybe more) for downloading the game. Locomotion uses close to all of the 8k rom and would not have been compatible. Playcable might have been cancelled by then anyway. Had they built the menu system in rom they should have got all 8k out of it. I like how it lights up the colour bars. Maybe one bar for each K loaded.

 

I'm confused ... I thought the hardware guy just told you it has 8K and showed Locomotion playing on it ... :?

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That's without the menu system. It definitely has 80kbit ram. There's no evidence that it supported 8K games like mazeatron, space spartans, or any 1983 games. Intellivisionlives says 8k games were a problem. Could they have found a way to make it work, I think so. But as far as I know, the system they had supported 6k games and not 8k.

 

Edit:

So, everytime you press reset would you have to download the game again, or would it jump to what it has in ram?

Edited by mr_me

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That's without the menu system. It definitely has 80kbit ram. There's no evidence that it supported 8K games like mazeatron, space spartans, or any 1983 games. Intellivisionlives says 8k games were a problem. Could they have found a way to make it work, I think so. But as far as I know, the system they had supported 6k games and not 8k.

 

Ah! :thumbsup:

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In a period of 3 years, could there not have been a PlayCable Rev 2, 3 with upgraded memory and what else needed to be improved?

Going by file size, I suppose the breakdown looks roughly like this regarding games that could fit into the memory with the menu system in place:

1978-1980: 10/10 games (100%)
1981: 9/15 games (60%)
1982: 11/26 games (42%)
1983: 3/21 games (14%)

which is a dwindling trend.

I may have missed some games, got the copyright year wrong as well as misanalysing how much of each 8 kilodecle ROM dumps is empty space, thus which ones would fit with the menu system in place.

 

(and yes, those numbers cover all publishers, not only Mattel)

Edited by carlsson

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Mattel wouldn't have cared about other publishers but including those games might not have been a bad idea. By the end of 1982 all Mattel cartridges would have been playcable compatible except Mazeatron (8k), Space Spartans (8k), B17 (12k), Bomb Squad (12k). I'm not sure when Vectron (12k), and Chess (8k+ram) were released exactly maybe very late 1982. They might have been less concerned about the voice games because it's a subset of the user base. It might have only been Mazeatron by the time their attention turned to the millions of dollars they were losing.

 

AD&D, locknchase, royal dealer, shark shark are all 6k cartridges.

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I'm supposing decle is making the Playcable to think it is actually connected to a service, using a modem chip and Arduino.

 

Of course, only a supposition because I don't know the actual Playcable hardware.

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It's not clear to me why an 8K game would have an issue. The code that loads the game and starts it resides in the PlayCable monitor at $4800 - $49FF; that is, unless the menu front end did need some code in RAM to drive the code at $4800 - $4FFF. (The "READY" string, for example, is in the PlayCable monitor.) Even if you needed a small driver loop to add add'l logic outside, you could copy it to System RAM and run it from there. Really, most of the logic is embedded in the PlayCable ROM.

 

While the BSR site says "8K and above," I suspect the real constraint is "above 8K", at least for games with a $5000 - $6FFF memory map.

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Back in 1982 when you turned on your Intellivision and PlayCable the first thing it downloads is a menu program and music and puts it in 2K of the 8K ram. Listen to the video below you will hear two gongs representing 2K. Then you hear the menu music. There's some more beeps and bleeps but the recording doesn't have any more gongs. The user selects a game from the menu using the keypad and playcable loads a different program from the cable stream based on the menu program. But there's only 6k of ram left to store that program. Is there any reason the game program can't overwrite the menu program. Maybe it should have worked. Maybe Tron Mazeatron was excluded because of licensing.

 

Is there anything interesting or surprising in the Playcable rom? Is the menu program in the rom?

 

https://www.youtube.com/watch?v=WvZp_k6s33o

Edited by mr_me

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Back in 1982 when you turned on your Intellivision and PlayCable the first thing it downloads is a menu program and music and puts it in 2K of the 8K ram. Listen to the video below you will hear two gongs representing 2K. Then you hear the menu music. There's some more beeps and bleeps but the recording doesn't have any more gongs. The user selects a game from the menu using the keypad and playcable loads a different program from the cable stream based on the menu program. But there's only 6k of ram left to store that program. Is there any reason the game program can't overwrite the menu program. Maybe it should have worked. Maybe Tron Mazeatron was excluded because of licensing.

 

Is there anything interesting or surprising in the Playcable rom? Is the menu program in the rom?

 

https://www.youtube.com/watch?v=WvZp_k6s33o

 

The PlayCable monitor has all the code necessary for tuning to a particular "channel", downloading and launching either the menu or a game. Once you've selected an item from the menu, the menu software merely needs to select a channel and jump to the loader in the PlayCable monitor.

 

None of the menu software needs to participate in that process once you've selected a game, so the entire PlayCable RAM can be replaced by the game. There's no reason to keep the menu resident either during loading or during the game. It only needs to be resident long enough to let you pick which channel to load from.

 

If you think about it, this isn't too surprising: The PlayCable monitor already needed to be able to load the menu without assistance. The difference between loading a game and loading the menu mainly comes down to which channel it's listening on.

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I agree, but there's no evidence of an 8k game on playcable. And Keith R was under the impression that 8k was too large. Maybe management used this as an excuse to keep cartridge sizes down. Gabriel Baum might know the answer. Without a copy of the menu program we won't know exactly what happens after a menu item is selected.

 

Can it actually tune different channel frequencies or would the different games be all coming down one stream on one channel.

 

Edit:

https://web.archive.org/web/20131129023025/https://www.cedmagazine.com/articles/2005/12/look-ma,-no-cartridge!

 

This is an article from 2005 that also mentions the 6k limit. It has a lot more details about playcable than what's on intellivisionlives. I'm thinking the writer had a source of information other than Keith's website.

Edited by mr_me
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I agree, but there's no evidence of an 8k game on playcable. And Keith R was under the impression that 8k was too large. Maybe management used this as an excuse to keep cartridge sizes down. Gabriel Baum might know the answer. Without a copy of the menu program we won't know exactly what happens after a menu item is selected.

 

Can it actually tune different channel frequencies or would the different games be all coming down one stream on one channel.

 

Edit:

https://web.archive.org/web/20131129023025/https://www.cedmagazine.com/articles/2005/12/look-ma,-no-cartridge!

 

This is an article from 2005 that also mentions the 6k limit. It has a lot more details about playcable than what's on intellivisionlives. I'm thinking the writer had a source of information other than Keith's website.

 

 

I think that 2005 article is just repeating Keith's mistaken assertion. This technical article (written by Charles Dages of Jerrold) describing the hardware states specifically the unit has an 80,000 bit capacity, saying it can support programs up to 80,000 bits directly, and can page larger programs in by downloading segments at run time.

 

And yes, it really is changing channels. There are 30 channels, 200kHz apart.

 

If there was a 6K limit anywhere, it's not in the unit or its ROM. It was in the head-end software or the programmers' heads.

1980-consumer-software-services-via-cable-television-systems.pdf

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I think that 2005 article is just repeating Keith's mistaken assertion. This technical article (written by Charles Dages of Jerrold) describing the hardware states specifically the unit has an 80,000 bit capacity, saying it can support programs up to 80,000 bits directly, and can page larger programs in by downloading segments at run time.

 

And yes, it really is changing channels. There are 30 channels, 200kHz apart.

 

If there was a 6K limit anywhere, it's not in the unit or its ROM. It was in the head-end software or the programmers' heads.

 

Yeah, I think the wording and structure of the article is too close to Keith's version of the same.

 

That said, both Stewart Schley's and Charlses Dages' articles were very interesting. Thanks for sharing them. :thumbsup:

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That's interesting that they addressed programs larger than 8k. I imagine 12k games like B17 Bomber or Vectron would have to be heavily modified to work on playcable.

 

They were supplying the service providers programs on floppy disk rather than cartridges. That means games could be on playcable months before appearing on store shelves.

 

The document also mentions that the plan was to support teletext data on playcable. In Mattel's marketing they suggested telephone modems.

 

----------

Stewart Schley would have had to have known 6k games existed. That's in addition to all the other details he wrote that's not on intellivisionlives.com. Other writers assumed the limitation was 4k games based on what Keith wrote. The 6k limit could have been real or a misunderstanding or typo but the origin might not be Keith R.

Edited by mr_me

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That's interesting that they addressed programs larger than 8k. I imagine 12k games like B17 Bomber or Vectron would have to be heavily modified to work on playcable.

 

They were supplying the service providers programs on floppy disk rather than cartridges. That means games could be on playcable months before appearing on store shelves.

 

The document also mentions that the plan was to support teletext data on playcable. In Mattel's marketing they suggested telephone modems.

 

 

Telephone modems would be required for any upstream communication. PlayCable was downstream only.

 

You're right, though, that games larger than 8K would need heavy modification to work. It would work best with games that could be divided into discrete stages (such as the levels of Thunder Castle), where you could afford a loading penalty between stages. B-17 Bomber probably wouldn't work, as around half of that ROM is voice data (according to Bill Fisher).

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This seems interesting... Not a lot of meat, though.

 

Perhaps the most interesting aspect is the priority date of April, 1978. That gives you an idea of how far back they were thinking about PlayCable.

US4247106.pdf

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Thanks for all the feedback and sorry to not reply sooner, I've been busy with the next bit... ;)

 

Did you just reverse engineer the fucking PlayCable?!

 

Err, yes. Yes we did. I have been working with JoeZ to understand RonTheCat's PlayCable and I have also been working with dave1dmarx to convert his audio recordings and recollections of the PlayCable in action, along with the one black and white picture, into a work-a-like system. You can see the results of this running in a hack version of JzIntv:

 

 

A big hat tip to both dave1dmarx and JoeZ for their help. I also need to thank my sons, hoalst and TheGreatSplurge, for their work transcribing the sound track. Even 30 seconds of the Entertainer is utterly beyond me. :dunce:

 

Edit: As pointed out by DZ-Jay below, I made a small flub in the video, each long ding represents 1K decles being loaded, not 4K as I stated. Apologies, and thanks to DZ for highlighting the error.

 

Wait! Where are you downloading that from? Who's broadcasting?

 

I'm supposing decle is making the Playcable to think it is actually connected to a service, using a modem chip and Arduino.

 

That red thing you're plugged into, is that a chip socket? Was it originally empty?

 

That would be me doing the broadcasting :). The two "chips" that can be seen on the white breadboard in the original video are:

 

post-46336-0-26549800-1540641699.png

  • Left - the ASIC that runs the digital part of the PlayCable
  • Right - a Teensy microcontroller

I moved the ASIC onto the breadboard from its original red socket to make probing it easier. The microcontroller is taking the place of the cable TV tuner in the PlayCable and feeds a digital TTL level data signal into the ASIC. All the connections to the ASIC other than the one, digital data stream input are just patched through from the red chip socket. The microcontroller is programmed to feed a fake PlayCable channel into the ASIC and from there, if you get the incoming data correct, the ASIC just does its thing.

 

Are you ICE'ing the data stream into the Playcable?

 

Anybody trying to recreate the modulated signal?

 

Yes and no, at least not yet (RonTheCat has aspirations).

 

Next up I will work on getting some decent pictures of the internals with a technical description and circuit schematics for distribution (if anyone with good analogue electronics experience fancies a preview and to contribute to the description, please let me know). After that I hope to coalesce the two parts of the project, with some tidy up courtesy of OSH Park over the next month or so :)

 

That's awesome. I think The playcable has five 16kbit ram chips.

 

That is correct, the PlayCable RAM is supplied by five 16K x 1bit DRAM chips. An interesting detail is that to get each decle for the Master Component the ASIC will have to access two memory locations in its DRAM and concatenate the 5 data bits in each together before sending it back.

 

there's no evidence of an 8k game on playcable. And Keith R was under the impression that 8k was too large. Maybe management used this as an excuse to keep cartridge sizes down... ...Without a copy of the menu program we won't know exactly what happens after a menu item is selected.

 

Can it actually tune different channel frequencies or would the different games be all coming down one stream on one channel.

 

Whilst we don't have the original menu code, and therefore, as you say, we cannot know what was done, there is no technical reason that 8K games with a standard memory map could not have been made to run, unaltered on the PlayCable adapter. As Joe says, the way the bootstrap software in the PlayCable is architected strongly suggests it was designed to allow games to use all 8K. Specifically, there is a mechanism for the menu to hand back control to the bootstrap ROM with a request to tune to a specific game channel and load a named game. In doing so, the menu can control things like whether the PlayCable screen is redrawn, whether the dings and block colouring occur, and whether the interstitial READY screen and fanfare, seen in the original video, appear (according to dave1dmarx they didn't, hence why they have been dropped in this second video). The details of the request, including the game name, could have been stored in scratchpad RAM by the menu. Now obviously this does not mean that constraints could not have existed elsewhere, for example:

  • PDP-11 head end - possible, but doubtful. A library of 20, 8K decle games would occupy 320KB, less than half the 1MB available on the floppy disk quoted in the Dages' document
  • Communications protocol - there are no constraints on program sizes
  • Non-functional requirements - For example, as has been highlighted, GI made a big thing about the 10 second average download time. In the IEEE paper on the PlayCable they compare the data rate with that of Teletext, which GI seems to have seen as the technology's primary market. If you compute the time to transfer 4K decles (8K bytes) at the 13.98KHz bit rate (this is correct by the way - the reason this unusual baud rate was chosen was probably because it is the Inty master clock and Colorburst frequency of 3.58MHz divided by 256) you get approximately 6 seconds. So adding on an average "seek" time of half the program length, the average time from selection to play would be 9 seconds. This and dave1dmarx's recollections suggest that while multiple games can be interleaved on a channel (each program on the stream has a header that identifies it), this was not done in practice. As download time is proportional to game length it is possible that either Mattel or GI/Jerrold might have placed an artificial cap on the game size to keep download times low.
  • Marketing / commercial / contractural reasons - let's face it, anything is possible and could well have been hidden from technical people.

Anyway I think that's about it for now.

 

 

Cheers

 

decle

Edited by decle
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Brilliant! :thumbsup: :thumbsup:

 

By the way, your video at some point mentions that the long "dings" represent each a 4K chunk of game data being downloaded, but it seems that each one is actually 1K of data (2 dings for the menu, which you say is less thank 2K; 4 dings for Baseball, which was part of the original 4K games; and 8 dings for the 8K Burgertime).

 

I guess it was just a slight inaccuracy in your unscripted speech. Nonetheless, it's all fantastic and very, very cool! :cool:

 

I can't wait to see what else you guys do with this. :)

 

-dZ.

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According to this, dave1dmarx has an audio recording of buzz bombers loading through playcable. If that is correct than it's evidence of playcable having 8K games in 1983. I should have known since I asked the question.

http://atariage.com/forums/topic/263689-playcable-menu-music/?p=3727197

 

That would mean that the only cartridges not compatible with playcable at that time were vectron, chess, bumpnjump, pinball, motu, three of the voice and all but one of the ecs cartridges.

Edited by mr_me

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