[Coco] CoCo 3 Plus in an FPGA

Sun Sep 6 00:57:25 EDT 2015

I think it's got some nice features but it lacks SRAM so you'd have to use the SDRAM which would add another level of complication to it.  Also, why pay extra for the ARM processor when you want it to be a CoCo?  I guess the ARM could be used as a high speed co-processor...or would the 6809 be considered the co-processor of the two? 😋  The cost is around a hundred bucks more.

Dave Philipsen

> On Sep 5, 2015, at 8:01 PM, tim franklinlabs.com <tim at franklinlabs.com> wrote:
> 
>   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
> <tim at franklinlabs.com.vcf>
> 
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