[Coco] Hello, all

[jdaggett at gate.net]

On 19 Jul 2006 at 8:09, Joel Ewy wrote:

> I've always been intrigued by these DMA controllers and wanted to do  something with them.  I realize that because of the way they work  they would have to be integrated into either the system bus or the  peripheral, but I think the latter could be done in a CoCo  system.  Without looking at the databooks I seem to remember  thinking that the 6844 needs some CPU signals that aren't brought out  to the cartridge connector.  But it probably doen't require so  many that one couldn't add some jumper wires...
>  
*****************

The DMA contrtoller would need acess to the TSC line and probably the AVMA, Halt, and/or 
LIC lines of the 6809E. The TSC input when asserted will put the address and data lines of 
the 6809E in tristate mode. The AVMA tells a copressor that the processor intends to use 
the buss in the next instruction cycle. The LIC pin tells peripherals that the last cycle of the 
current instruction is being executed. The 6809 itself has the handshake lines built in to 
handle the DMA controller along with the clock generator. The 6809E actually makes a good 
slave processor in a two processor setup. The registers in the DMA chip are memory 
mapped. 
 
>   You seem to be suggesting that you have one of those Motorola  SBCs?  I don't have one of those, but I do have a couple M68MM17  Micromodules.  These are meant to be used in an EXORbus system,  but can be stand-alone SBCs.  They have a 6809, a 6821, a 6840  PTM, a couple 6850s, and 5 28-pin sockets for (EP)ROM or SRAMs.   I've taken a few tentative steps toward getting a 6809 tiny BASIC to  run on one of them.  Ultimately it would be nice to have OS-9 on  one running from ROM, but that's a ways off.
> 
*******************

I do. Never finished assembling it. I have all the ICs and most of the resistors and caps. The 
original Flex disks that I  have are  8 inch disks and I never really desired to build the 
system up with 8 inch drives. 5.25 inch drives were a bit pricy back in 1983. The board is 
huge, about 12 inches by 9 inches. The bare boards were available for employees. 

james
  
>   JCE
> 
> jdaggett at gate.net wrote:  The MC6844 was in full production. While never used with the Coco, it could be incorarated 
> into the board though. Motorola had designed and then canceled a single board computer 
> that was based on the 6809. It used the 6844 along with two 6821, two 6850, NEC 765 
> Floppy controller, 6845 as the video controller, and a 68488 buss controller chip. 64K of ram 
> with 32K of video ram. There was an expansion board that expanded memory to 128K. The 
> system would run Flex or OS9 Level I. I never got the OS9 OS for it but now wished I had. 
> Just for the NEC765 floppy disk driver would be nice. 
> 
> james 
> 
> On 17 Jul 2006 at 18:20, Joel Ewy wrote:
> 
> >   And finally, for the CoCo hackers out there:  I have a small  number (10
> >   or less) of MC68B44 DMA controller chips.  I suspect  these are fairly
> >   uncommon.  Were these even manufactured in large  quantities?  It is
> >   entirely possible that these were just  engneering samples.  In any
> >   case, I haven't had any way to test  them short of wiring up some kind
> >   of test circuit and hooking it up to  a CoCo, which I simply haven't
> >   done yet.  Is anybody else  interested in playing with such things just
> >   for fun?  Even though  they don't seem to be available in any sort of
> >   quantities, they could  surely be emulated in an FPGA design or possibly
> >   in one of the larger  CPLDs.  The actual parts could be used in a design
> >   process for,  say, a new disk controller, where you test an HDL version
> >   against the  real McCoy.
> 
> 
> 
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