[Coco] CoCo 3 68000/RAM board project

[Steve Bjork]

James, please tell Bookworm the price for adding something like this to 
a CoCo.  I don't think he caught it in your post.

Also, 1,790,000 16-bit words per second does not make for a very fast 
memory interface. (Even a two decades old system.) It would had press to 
get a better graphics with that slow of memory. An 800 by 600 by 256 
color graphics mode would need a memory speed of 15,000,000 16-bit words 
per second and triple that speed for true (24-bit) color mode.

But speed is not the only issue.  It would take 480K bytes just to 
display an 800 by 600 bye 256 color screen.  There would be no room left 
in the CoCo's memory to run anything but a Mega-Bug ROM game.

You could expand the memory limit while you updating the GIME to 2 
megabytes since it's easy to add the extra bits to the MMU.  But you are 
still limits how fast you can access the memory and a full screen update 
would take 500 ms (about 1/2 second) and that makes the game frame rate 
of 2 per second.  Too slow in my book.

The CoCo screen resolution was kept low not just because of the memory 
limit but the speed of updating the memory.  The speed of the Coco was a 
wall that I hit time and time again when creating my games for Tandy.

Steve (Z-89) Bjork

jdaggett at gate.net wrote:
> It is a essentially a replacement Coco but done in either two or three 
> FPGAs. Currently I am lenaing towards three FPGAs. This can be used as 
> an embedded sytem or as a stand alone system. 
>
> What I am about to share is a work that I started several years ago and has 
> undergone several intese modifications. First off was to do a Coco3 into a 
> single FPGA. While that is doable, in fact has been. None of the 
> development boards out there that are under $300 in cost are lacking in 
> either I/O or VGA color depth withour modification. 
>
> This all coincided with my understanding of several handheld computers 
> that are out there to control a telescope. Two in particular use a processor 
> that runs no faster than a Coco3. To give it in a nutshell, I decided to 
> investigate using a Coco3 for a telescope controller. To my surprise it can 
> be very well adapted to such a task with some external motor drivers. 
>
> The main sticking point is that setting up a laptop, and a coco system is a 
> bit to much for the field use in a remote area. I need a Coco3 that is small 
> and portable. No bulky disk drives and monitor. Just the computer, a small 
> LCD, and a flash drive. 
>
> The current direction is now more in line with what Sockmaster had 
> proposed years ago which at first I rejected. Now in retrospect some of his 
> ideas are not bad all. One FPGA will house the CPU and any 
> enhancements to the instruction set like a math coprossesor. The second 
> chip is the main guts of the GIME chip like the MMU, registers and such. 
> The third FPGA is the actual video section. All are separate boards and are 
> plugable into a main board that is but a carrier. A fourth board will have the 
> Vinculum chip that gives me direct access to a USB flash drive for storage. 
> The Vinculum chip handles all the FAT issues for drive access. 
>
> Like I stated it started from first being a GIME replacement into a Coco3 
> that has grown maybe out of proportion. But size is now a driving factor and 
> the ability to operate off of batteries. 
>
> i hope this is less than a minute but a synopsis of what I am doing. I am 
> hoping to have some form of a working unit by the end of the summer. I 
> finally have the finances and hopefully the time to realize a dream of mine 
> for the last four years. Also to learn something in the process. 
>
>
> james
>
>