[Coco] CoCo 3 Plus in an FPGA

tim franklinlabs.com tim at franklinlabs.com
Sat Sep 5 21:01:36 EDT 2015


   Has anyone tried/experimented with the DE-1 SoC?

   [1]http://www.terasic.com.tw/cgi-bin/page/archive.pl?Language=English&N
   o=836

   Looks like a modified DE1 with new features.

     On September 5, 2015 at 6:30 PM Salvador Garcia
     <ssalvadorgarcia at netscape.net> wrote:
     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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References

   1. http://www.terasic.com.tw/cgi-bin/page/archive.pl?Language=English&No=836
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