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The MBX Expansion System


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#1 jaybird3rd ONLINE  

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Posted Tue Nov 23, 2010 2:25 AM

After admiring it from afar for many years, I finally took the plunge and added a boxed MBX Expansion System to my 99/4A collection this past week:

Attached File  mbx.jpg   858.2KB   16 downloads

I've only used it a few times so far, but I think it's a fascinating add-on for the 99/4A, and it's such a pity that its potential was never fully explored. I've looked at the MBX pages on the 99/4A Videogame House site, and I'll definitely be picking up more of the MBX-enabled games as I can afford them; the only two that I have right now are Superfly and Soundtrack Trolley.

My main question about it is: how much technical information is available for the MBX? I'm especially interested in programming resources: how to detect the MBX, the protocol that is used to communicate with it through the 99/4A's joystick port, how to access its various features, and so forth. It might be fun to add support for the MBX to future 99/4A homebrew games, if I ever get around to writing them.

Another (obvious) question: any MBX game recommendations? :)

#2 Opry99er OFFLINE  

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Posted Tue Nov 23, 2010 4:32 AM

The documentation is pretty full.... Tursi and Marc Hull know quite a bit about how it works.... Jim Fetzner as well. I have Marc Hull's MBX at my place right now. :). As far as programming for it, that has been talked about too. Do-able for sure... I think it uses the tape DSR (if there is such a thing)...

#3 marc.hull OFFLINE  

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Posted Tue Nov 23, 2010 8:15 AM

The documentation is pretty full.... Tursi and Marc Hull know quite a bit about how it works.... Jim Fetzner as well. I have Marc Hull's MBX at my place right now. :). As far as programming for it, that has been talked about too. Do-able for sure... I think it uses the tape DSR (if there is such a thing)...


Don't make me out for an expert or even well versed for that matter.... ;-)

The things I do know are...

1) The MBX is more or less a stand alone computer that is connected through some proprietary serial interface using the joystick connector and it's assigned CRU bits.

2) In order to do home-brews for it you will have to know both 9900 and Z80 ML as well as get info on the architecture of the MBX.

3) This is way above my head ;-).

#4 Tursi OFFLINE  

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Posted Sat Nov 27, 2010 7:21 AM

The documentation is pretty full.... Tursi and Marc Hull know quite a bit about how it works.... Jim Fetzner as well. I have Marc Hull's MBX at my place right now. :). As far as programming for it, that has been talked about too. Do-able for sure... I think it uses the tape DSR (if there is such a thing)...


Actually, I don't know anything about the MBX either. I think I may have seen one in RL once... ;)

I have some old newsgroup posts about it in the hope of providing some kind of support for it someday in Classic99, but don't hold your breath. :)

#5 matthew180 OFFLINE  

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Posted Fri Jan 21, 2011 11:19 PM

Having opened one to repair it for another TIer, this is what I have learned:

* I have not looked very hard, but I could not find any schematics or details about the unit's internals, let alone programming the thing.

* Socketed: The main CPU is a 6809 which is an 8-bit CPU with some 16-bit features. It was designed to be source compatible with the 6800 and 6502, so you did any assembly on an Apple or C64, then you will have a head start on the MBX.

* There is a 6821 I/O Chip.

* There are two 6116 SRAMs (2Kx8) which would give the unit 4K of 8-bit RAM.

* Uses an ADC0809 for analogue to digital conversion, and is still available! Must be a useful and easy to use ADC chip! http://www.national....9.html#Overview

* Socketed: MM52664MBX/N that I could find nothing about. This is probably the ROM since the part number has MBX in it - but that is totally speculation.

* Socketed: GI8335 that I could not find any useful information on either, but this is probably the sound / speech chip.

* A LM386N-1 Low Voltage Audio Power Amplifier drives the internal speaker and runs off of a separate Zener diode (1N4839 8.2V) regulated supply voltage from the main 7805 regulator. Why? I have no idea since the LM386 will operate from 4V to 12V, and the main board 5V seems like it would be just fine. Also, I/O pin 19 (C2) on the 6821 controls the output gain of the LM386 by pulling pin 5 to ground via a 2N3904 transistor. It seems that the internal speaker can be either on or off, i.e. no volume control.

* The main regulator (LM7805) for the board has a really stupid off-board placement and can easily be broken off if you are not very careful when taking the unit apart. The 7805 is very robust and can deal with inputs from about 7.2V to 35V. The secondary Zener regulator (mentioned above) can deal with inputs up to about the same 35V. The 7805 is rated at 1A, and the 1N4738 Zener is rated for 200mA, so the whole unit can never draw more than 1.2A (or the regulators will fail.) Most of the electrolytic caps in the unit are rated for 16V. Thus, you could safely power the unit with any DC supply from about 9V to 12V @ 1A. The tip is positive. 9V is better since the regulators don't have to work so hard and will run cooler.

* The secondary Zener regulator mentioned above *seems* to only power the LM386 amp. The main unregulated input voltage is fed to the collector a 2N3904 transistor (not the same one mentioned above that controls the gain of the LM386). The base bias is set via a 200Ohm resistor and the 1N4738 Zener which keeps the base at 8.2V. The emitter is the output and connects the the LM386. From my electronic school days, this configuration would probably be known as an "emitter follower".

* The top and bottom of the main board are covered with a metal shell that uses "twisted" tabs to keep them on. While not very hard to remove, you can only un-twist them so many times before they will break off. At least they didn't solder the shields to the board!

* There is no crystal for the main oscillator, which I find strange since they are not really that expensive?! However, a quick check with the my O-Scope on pin 38 shows a nice 6.038MHz clock signal.

* Connections to the 99/4A are via the joystick and cassette ports. The joystick port is probably used as a serial interface, or maybe a 4-bit parallel interface. But these are just guesses. I thought the cassette interface would be to get sounds from the MBX to come out of the 99/4A's speaker, but that does not seem to be the case. However, since the 99/4A can read data from a cassette, there is no reason that the audio data input could not be computer generated... And, unlike the joystick port, the cassette port is a bidirectional data port! Now that I think about it, that makes more sense. The MBX and 99/4A can talk to each other, albeit slowly, via the cassette interface.

* The mic input jack seems to only be that, a mic input. I tried connecting a headphone / mic headset up to the jack, but the audio did not come out of the headphones.

* The board is really clean and well laid out. Kind of reminds me of my MSX1.

The MBX is a full blown computer only lacking a video subsystem, and it is hard to believe it was an "expansion". With an 8/16-bit CPU running at 6MHz, it kind of puts the 99/4A to shame. It is a better computer than the system it was designed to hook up to.

#6 jaybird3rd ONLINE  

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Posted Sat Jan 22, 2011 1:33 AM

Very interesting. Thanks for sharing that information. I remember reading (on the Videogame House MBX page) that the MBX was indeed intended to be a standalone game console from Milton Bradley. The console was canceled after Coleco entered the market with the ColecoVision, and was repackaged as an add-on for the 99/4A (presumably because Milton Bradley had a relationship with TI and had developed the Gamevision titles for them). It was also supposed to become the Voice Commander, a similar add-on for the Atari consoles, but apparently that project was canceled also. The Atari Space Age Joystick was designed by Milton Bradley for Atari, and it is clearly derived from the MBX joystick design.

I'll be opening the system to take pictures of the interior, and while I have it open, I'll have to see about dumping the ROM chip (if in fact it is an 8K ROM, as suggested by the part number). It could reveal some clues about how the system works. The MBX's cassette port plug is labeled as a "grounding plug," but it has three wires connected in it, so it might also be used for other purposes. It's too bad there don't seem to be any datasheets readily available for the GI8335; that would be an important part of reverse-engineering the MBX.

#7 matthew180 OFFLINE  

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Posted Sat Jan 22, 2011 10:43 AM

The MBX is definitely a good start on a stand alone computer, especially for the era. I would be curious to know what kind of video subsystem they were planning.

I didn't even think about trying to dump the ROM... I guess it has to be that MBX part number chip, since there has to be a ROM and all the other chips are pretty well identified. I can check the traces on the board to see if they match a standard ROM pin out. At the very least, the VSS and GND pins need to be identified to make sure trying to read the chip won't blow it up. I don't know how worried about copy protection MB was, but enough to have their own ROM manufactured.

#8 humeur OFFLINE  

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Posted Sat Jan 22, 2011 2:46 PM

Having opened one to repair it for another TIer, this is what I have learned:

*

* Socketed: GI8335 that I could not find any useful information on either, but this is probably the sound / speech chip.



perhaps this ??

http://www.e-clec-te...256al2chip.html

jean louis

#9 matthew180 OFFLINE  

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Posted Sat Jan 22, 2011 4:35 PM

Hmm. I suppose it could be that chip with a different part number. The voice that come from the unit is not really robotic though. That's good info to have though, and a datasheet too! Thanks!

#10 marc.hull OFFLINE  

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Posted Wed Jan 26, 2011 10:25 AM

Not to butt in to your thread but a point I think should be noted. It is pretty easy to treat the MBX like a joystick and just plug it in while everything is hot. It should be noted though that you are basically hooking two computers together and you can cause havoc by doing this. The only MBX I have repaired had two blown 4 bit driver/buffers that handled the joystick interface because someone most likely did just this (aside from the broken VR that Matt mentioned earlier.) When using the MBX the joystick port becomes a serial interface so be careful 8-O.

#11 jaybird3rd ONLINE  

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Posted Wed Jan 26, 2011 11:24 AM

Not to butt in to your thread but a point I think should be noted. It is pretty easy to treat the MBX like a joystick and just plug it in while everything is hot. It should be noted though that you are basically hooking two computers together and you can cause havoc by doing this. The only MBX I have repaired had two blown 4 bit driver/buffers that handled the joystick interface because someone most likely did just this (aside from the broken VR that Matt mentioned earlier.) When using the MBX the joystick port becomes a serial interface so be careful 8-O.

Duly noted. I usually plug everything in before turning it on, just to be on the safe side, but it's good to know that we should always do this for the MBX in particular.

I just realized that I forgot to follow through with the ROM dump and the additional pictures. I'll try to find time tonight.

#12 S1500 OFFLINE  

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Posted Wed Jan 26, 2011 11:36 AM

It would be interesting to see what homebrew love could be given to this goofy contraption. The controller stick kicks ass. 4 buttons + a paddle? Aww yeah. Voice control before Seaman ever was invented? Amazing!

Yeah it is like attaching some sort of nuclear fusion engine to a Yugo.

#13 OLD CS1 OFFLINE  

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Posted Wed Jan 26, 2011 6:04 PM

Yeah it is like attaching some sort of nuclear fusion engine to a Yugo.


I am rather distressed that you compared the TI-99 console to a Yugo. I will let you decided which way bothers me, and you will probably be correct ;)

#14 marc.hull OFFLINE  

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Posted Thu Jan 27, 2011 9:29 AM

Yeah it is like attaching some sort of nuclear fusion engine to a Yugo.


I am rather distressed that you compared the TI-99 console to a Yugo. I will let you decided which way bothers me, and you will probably be correct ;)


I agree. It's a totally unfair comparison! The Yugo's production life was over twice the TI's ;-) Sorry couldn't help myself....

#15 retroclouds OFFLINE  

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Posted Mon Feb 7, 2011 12:46 PM

Going through some of the folders on my USB thumb drive I just found below:

Attached File  mbx.zip   31.91KB   19 downloads

From the readme:

This source code released in the hopes that perhaps someone may yet find it useful.

If you find this code useful, I'd love to hear about it! Email me at *****************
and let me know.

The files in this zipfile are as follows:

MBX_S - Main source file, has include directives for most of the other files.
When assembled, it creates a diagnostic utility for testing out the various
features of the MBX. It also contains ALL THE LIBRARIES YOU'D EVER NEED to
program an MBX.

MBX1/MBX2 are the resultant E/A #5 files that you can create from MBX_S. They have TIFILES
headers on them.

XB_S - I was working on a set of CALL LINK's that could be accessed from TI's XBasic
and I actually had this working well enough to demo at Chicago/Milwaukee one
year long ago. You could use speech recog, the joystick and keypad, all from
XB. I'm not sure which version of the XB source this is, or how well it works, but
I imagine it can be made to work without too much trouble.

The MBX is communicated with via the joystick port. Basically, you issue commands to the MBX in the form of a send queue, and wait for responses from the receive queue. An interrupt routine (the 60Hz interrupt) is used to manage communications to/from the unit.

I'd love to see any derivative work spawned by this source code.

Enjoy!



#16 matthew180 OFFLINE  

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Posted Mon Feb 7, 2011 1:40 PM

That's a pretty neat find. Too bad the MBX is not more readily available. It would be interesting to get some stats on what the unit was capable of doing. Just using one, it is hard to know what is happening inside the MBX and what the 99/4A is doing.

#17 retroclouds OFFLINE  

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Posted Sat Feb 12, 2011 12:55 PM

This is kinda scary :D

Today I browsed through the current "Retro" issue at the local newspaper shop. Guess what they have in there.....

A short review of the MBX system. Now how cool is that? First of all that they even mentioned the TI-99/4A and secondly they know the MBX system.
They have a photo and some schematic drawing in there.
It was part of an article called "Yestersdays' future" in which they review cool hardware that never really took off.

Wonder if they lurk here ;)

They also have a website http://www.retromagazine.eu/retro

#18 Opry99er OFFLINE  

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Posted Sun Feb 13, 2011 5:48 AM

Fascinating, man!! I'm intrigued to know what's in MBX_S. :) "ALL the libraries you'll ever need to program an MBX. Must be quite a file!!! :)

#19 matthew180 OFFLINE  

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Posted Sun Feb 13, 2011 11:31 AM

Does not look like you can read the magazine online? If I could read German I would order the magazine...

#20 save2600 ONLINE  

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Posted Sun Feb 13, 2011 11:57 AM

I always wanted to play Championship Baseball on one of these. Someday, when a bunch of NOS are discovered in South America maybe Posted Image

As far as programming homebrews for it... yeah, that would be all fine and dandy. FOR THE THREE FRIGGIN' PEOPLE THAT OWN AN MBX! Posted Image

#21 matthew180 OFFLINE  

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Posted Sun Feb 13, 2011 1:00 PM

Yup, that's the problem with the 3rd party 99/4A hardware, it was only available for a very limited time and there is not much of it floating around these days. When I had the MBX I was fixing, one of the games the guy sent for testing was the baseball game. It was pretty cool for two players, since one person used the MBX joystick (the hitter) and the other person (the pitcher) used the MBX "pad" (the main unit with all the programmable buttons - I'm not sure if it has a proper name.) The overlay for the MBX let you choose the type of pitch to throw. You had quite a few variations since you could select the speed (fast, medium, slow) and type (inside, middle, outside, curve). It took me a while to realize what was going on and what to do. I could see this kind of thing being very cool with the right kind of games. It would definitely made games like ToD much faster and easier to navigate and control (especially for stuff like pulling up the maps, stats, store interaction, etc.) I better stop talking or I'll make Owen want to use the MBX for his CRPG. ;)

#22 Opry99er OFFLINE  

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Posted Sun Feb 13, 2011 2:43 PM

Ha!!! If I use any 3rd party stuff, it'll be AMS... But I'm still leaning towards stock TI with multiple disks--- an optimized version for the CF7, and an extremely modified version for the "wrap." Good try though.... :) i wish there were more MBXes out there.... I love mine, and can attest to the fact that Baseball is VERY cool. :)




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