TMS9928 related to Colecovision

[Itchy Scratchy]

Technical question that needs insider info.

 

I have several versions of the TI 9928 book including an original I received in 1984 just by calling Texas Instrument.

 

The way I understand it is the Chip itself has a basic type of BIOS.

I also understand that this is locked inside the Colecovision.

 

However, a...Could a jumper unlock it (doubtful)

but b...

Is this bios a standard generic bios or one written for the Colecovision environment itself.

 

Knowing a bit about chips that most of these are write once but some if you add voltage on certain pins they can be written to.

 

I know this is above a lot of peoples pay grade but hopefully one of you knows just enough that may lead to more information.

Maybe something Howard Eglowstein can answer if he pokes his head around here on occasion.

I know he does over on the ADAM Facebook page.

 

Edited January 5, 2021 by Itchy Scratchy

[ChildOfCv]

The 9928 is just a graphics chip.  No BIOS.  It does need 8 RAM chips though.

[Itchy Scratchy]

1 hour ago, ChildOfCv said:

The 9928 is just a graphics chip.  No BIOS.  It does need 8 RAM chips though.

Not to argue with you but understand.

I have toyed with and become fairly good at programing the Colecovision without knowing 100% every nut and bolt so this is my own learning.

 

I understand the functionality of how to get what I want out of the chip but same as the Colecovision itself, not every signal on the pin.

 

So, this is in the TI Programing manual itself.

Is this just some example code then for a generic assembly code.

 

 

 

One quick snippet

 

TMS9918 - Graphics Chip.pdf

Edited January 6, 2021 by Itchy Scratchy

[ChildOfCv]

That's TMS9900 assembly language.  If you used the TMS9928/29/18 in a system with a TMS9900 microprocessor, that is the code that the microprocessor would run for those demos.

 

Colecovision has a Z80 instead.  Colecovision's BIOS, Z80 code, has some routines to program the TMS9928 and support games.

 

But none of that is stored within the TMS9928, regardless of architecture.  CV stores its routines within the ROM chip.  There is fully commented source listing of the CV ROM program and its support functions in the ColecoVision Programmer's Reference.

 

If your aim is to figure out how to program the chip in your own hardware, then study the data book for the 9928/29/18.  It tells you what data to send where, and when.  If you familiarize yourself with TMS9900 assembly language, you can also see how their example program performs those feats.  Just note, however, that the TMS9928 does not decode address lines, so it's up to your hardware where in the address space you put it, and you need to build the decoding circuitry to activate it only on the right addresses.

[Itchy Scratchy]

24 minutes ago, ChildOfCv said:

That's TMS9900 assembly language.  If you used the TMS9928/29/18 in a system with a TMS9900 microprocessor, that is the code that the microprocessor would run for those demos.

 

Colecovision has a Z80 instead.  Colecovision's BIOS, Z80 code, has some routines to program the TMS9928 and support games.

 

But none of that is stored within the TMS9928, regardless of architecture.  CV stores its routines within the ROM chip.  There is fully commented source listing of the CV ROM program and its support functions in the ColecoVision Programmer's Reference.

 

If your aim is to figure out how to program the chip in your own hardware, then study the data book for the 9928/29/18.  It tells you what data to send where, and when.  If you familiarize yourself with TMS9900 assembly language, you can also see how their example program performs those feats.  Just note, however, that the TMS9928 does not decode address lines, so it's up to your hardware where in the address space you put it, and you need to build the decoding circuitry to activate it only on the right addresses.

I got the rest but my thinking that there was a rudimentary type of bios like programing a pic chip but hey, I learned something new.

 

My next question is what's up with the external video signal on the Colecovision and why hasn't anyone modified the system to piggy back.

 

I usually ask myself these things after a couple shots of scotch.

Edited January 6, 2021 by Itchy Scratchy

[ChildOfCv]

It's easier with a 9918 because it has an external source input pin, so you can piggyback them pretty easily.  9928/29 don't have an external source though.  The suggested method for doubling them is to have one be the master, and if it is showing any color difference, that turns on the master output buffer and turns off the slave.  When the master is not showing any color difference, the slave's buffers are turned on and the master's turned off.

 

The remaining issue is to patch it into the address space (though I think there may be some unused I/O selector pins, at least if not adding the Adam to the system), patch it in, and then write programs to take advantage of it.

 

But for most people, the SGM probably does well enough at improving the system's capabilities.