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jaybird3rd

The MBX Expansion System

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especially considering how little software there is available commercially until someone smarter than I figured out to to make MBX games (talk about niche in a niche, lol)

 

that's why i was thinking that having some kind of after-market box to emulate it would be super cool. (this also was prompted by the question on the FB group about the overlays).

 

i'm not sure quite how the overlay functionality would work- maybe physical buttons or something? reprinted smaller overlays?

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Hey, you count me in that four or five owners of an MBX? I also have two SuperSketches. :)

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i have a good number of the carts (i think i'm only lacking one maybe)- so itd be cool to mess with :) even the educational ones are kinda fun, hehe

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especially considering how little software there is available commercially until someone smarter than I figured out to to make MBX games (talk about niche in a niche, lol)

 

that's why i was thinking that having some kind of after-market box to emulate it would be super cool. (this also was prompted by the question on the FB group about the overlays).

 

i'm not sure quite how the overlay functionality would work- maybe physical buttons or something? reprinted smaller overlays?

 

touch screen lcd :)

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I am also the proud owner of a boxed Super Sketch as wel!! icon_smile.gif

 

mine is well used, as there is a ti-artist driver to use it, had to do some quickswitch on the ports once tia was loaded to make it work..

 

Greg

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I have a MBX, but no Sketch. I do also have a Triton Turbo XT box and cables (the computer itself is long since gone) since it was mentioned previously in the thread.

 

I agree with digdugnate as would like to see an emulator device too. Ideally, it would accept USB joysticks and I also suspect that a USB numeric keypad could replicate the overlay system. Although you wouldn't have printed overlays, you could match the keys with the corresponding item. There certainly would be some tricky parts to the keypad as there were different overlay keys for each of the games. But, from the ones I have, I think there are enough keys to emulate most of them. (Although via a key combination.)

 

Sadly, I'm no good on the hardware side or I'd try messing around with it.

Edited by rickneff68

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I have one of each too, so I guess there are really a lot more than three of us out there. . .maybe 30 or so, LOL

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One MBX and all the carts(Hasn't seen the light of day in 20 years) - Two Super Sketches (same schedule as the MBX)

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I have two MBX systems and a Super Sketch. The MBX headphones need new mic and earpiece foam.

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I have two MBX systems and a Super Sketch. The MBX headphones need new mic and earpiece foam.

 

For the foam pads, you can just run down to Radi---- awww... never mind.

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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.com/mpf/DC/ADC0809.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.

 

Just curious, has a schematic for the MBX ever been located?

 

Thank you,

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On 3/7/2018 at 9:30 PM, sparkdrummer said:

One MBX and all the carts(Hasn't seen the light of day in 20 years) - Two Super Sketches (same schedule as the MBX)

Hey Mr. Curmudgeon!  Let's fire it up at ye ole donut shoppe at the next VAST meetup?! 

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On 2/7/2011 at 11:46 AM, retroclouds said:

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

 

mbx.zipUnavailable

 

From the readme:

 

   This thread’s post #15 seems to contain all of the keys to MBX programming knowledge. How cool will it be if one of the current TI Programming JediMasters were to dissect this MBX Rosetta Stone and publish his findings. 

 

   Oh how I’d love to read an instructional pdf on programming the MBX. This device just may be the one TI-99/4A peripheral with the most untapped potential. 

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2 minutes ago, Airshack said:

   This thread’s post #15 seems to contain all of the keys to MBX programming knowledge. How cool will it be if one of the current TI Programming JediMasters were to dissect this MBX Rosetta Stone and publish his findings. 

 

   Oh how I’d love to read an instructional pdf on programming the MBX. This device just may be the one TI-99/4A peripheral with the most untapped potential. 

And then badger Tursi for MBX support in classic99. ;-)

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55 minutes ago, jrhodes said:

And then badger Tursi for MBX support in classic99. ;-)

Not going to happen, most likely. MBX is a separate computer, I never owned one, and I don't plan to write software for it. That sort of thing is way more appropriate to MAME, which already has all the pieces coded and just needs them linked together. ;)

 

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On 2/7/2011 at 10:46 AM, retroclouds said:

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

 

mbx.zip 31.91 kB · 77 downloads

 

From the readme:

 

Hey @retroclouds , When I load the file MBX_S into Classic99 by  @Tursi all I get is the "ONE MOMENT PLEASE..." deal -- forever. 

 

Strange how this was produced with little to no documentation. Am I missing something here? The readme.txt is so encouraging.

 

I wish I had these files in a .pdf or .txt file for examination. Loading into E/A removes control characters so all I see with the editor is scrambled code. Looks like the Emergency Action Messages I used to decode back in SAC.

 

Again, I can not make out any documentation?? Bob has apparently supplied the keys to the kingdom of MBX yet I find myself pounding on the front door because it wont open.

 

Help! 

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