[Coco] CoCo 3 Plus in an FPGA

[Salvador Garcia]

I would be happy with a SATA port :-) Salvador




-----Original Message-----
From: Dave Philipsen <dave at davebiz.com>
To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Sent: Sat, Sep 5, 2015 5:43 pm
Subject: Re: [Coco] CoCo 3 Plus in an FPGA


And just to add a little to what Aaron said, the FPGA is a single chip 
on the
DE1 board. You could think of the FPGA as a bucket full of logic 
chips.  The
'programming' that is applied to it is like the wires (or 
traces) that connect
all of the chips together.  If I gave you an 
unlimited supply of logic chips
and asked you to build a 6809 CPU it 
could be done with a lot of wire and
patience. What Gary is doing with 
the programming is designing a complex
circuit out of a bunch of fairly 
simple gates (logic elements).  In addition to
the FPGA chip the DE1 
board contains some other support chips, connectors, and
sockets for 
VGA, sound, SD card, keyboard, etc.  It also contains some
expansion 
pins as Aaron explained.  These pins can also be 'programmed' to act
in 
different ways.  In theory, it would be possible with some extra

interfacing to design a CoCo bus connector from the available I/O pins.  
In my
opinion it would be very possible since the logic to do that is 
less complex
than the GIME chip and since many of the signals that would 
appear on that
interface are already available internally (in the FPGA). 
Gary had mentioned to
me not too long ago that he had used less than 
half of the available logic
elements in the FPGA so apparently there 
would be plenty of 'logic' left to
implement an external bus.

As far as implementing things like serial ports,
cassette interfaces, 
joystick ports, and the like, the logic elements are there
to do it so 
all that is required is to add some hardware to interface that
digital 
logic to the outside world.

So if you think about the RS232 port which
is on the DE1 board it is not 
necessarily tied to an 'RS232 port' per se
internal to the FPGA.  It is 
simply connected to some I/O pins which can be
'programmed' to do what 
ever you want with them.  The port could be synthesized
as 6551 UART 
such as is used in the RS232 pak or it could be synthesized as a

'bit-banger' port as is used on the CoCo 3, or it could be synthesized 
as an
8530, a 16650, 68681, etc., etc. Same is true with the signals 
that are used to
drive the VGA interface.  With the proper 
're-programming' and interface
circuitry one could easily implement a 
CGA, EGA, Hercules, or other form of
display port.  In that case the 
limiting factor might be the frequency of the
dot clock.  Going higher 
than 640x480 at 60 Hz might involve some additional
hardware or the use 
of PLLs or something (I believe the FPGA has some PLLs
onboard).

So to sum it up the CoCo3 FPGA project on the DE1 board has audio

output, VGA, serial port, PS/2 keyboard, SD card, and probably a few 
other
things that we don't even know about yet.  The fact that the DE1 
board has two
expansion ports means that other things could be added in 
the future to the
project just by simply designing the circuitry for the 
expansion ports and
implementing the desired logic.

Gary has mentioned in the past that he will
package up the source code 
and make it available.  At that point, if you wanted
to have a CoCo 3 
with eight serial ports it would be entirely possible to
design such a 
thing and without too much difficulty!  Or perhaps you wanted
another 
VGA output, another SD card, a MIDI port, an ethernet port, a WiFi
card, 
etc.  They would all be within the realm of possibility if you could

design the appropriate circuitry and write the code required to 
implement
them.  In my opinion the whole project is a very cool idea.  
If you just want a
CoCo 3 that runs at 25 MHz (albeit without expansion 
bus) then you just take it
as it is.  If you want to customize it and 
make something special then hack
away! If Gary does indeed release the 
source at some point then it may be up to
some enterprising person to 
come up with a new feature that can be added on in
the future.

Dave Philipsen



On , Salvador Garcia wrote:
> Some one correct or
confirm my response :-) No, the FPGA does not have
> the 40 pin expansion slot
and it does not have the same ports as the
> Color Computer line of computers.
The FPGA implementation uses the
> Terasic DE1 which is a field programmable
gate array. The gate array
> is "programmed" so that it emulates a Color
Computer 3. The ports that
> are available are those that are inherent to the
FPGA.
> 
> 
> Here is a page with info:
> 
> 
>
http://www.terasic.com.tw/cgi-bin/page/archive.pl?No=83
> 
> 
> 
> Salvador
> 
>

> 
> -----Original Message-----
> From: Michael Brant
<brant.michael.l at gmail.com>
> To: CoCoList for Color Computer Enthusiasts
<coco at maltedmedia.com>
> Sent: Sat, Sep 5, 2015 11:36 am
> Subject: Re: [Coco]
CoCo 3 Plus in an FPGA
> 
> 
> If it has that and the other ports i will be so
very interested
> On Sep 5, 2015
> 12:35 PM, "George Ramsower"
<georgera at gvtc.com> wrote:
> 
>>  This thing has piqued
> my interest.
>>  Will
it have the equivalent of the 40 pin expansion slot?
>> 
>> 
> George R.
>> 
>>
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