[Coco] CoCo 3 FPGA? (Really long message)

[Joel Ewy]

Thanks for the update and clarification, Gary.  I'm excited to hear
it'll probably run at 16 MHz -- that ain't too shabby.

JCE

Becker, Gary wrote:
> Since I have not done any documentation on the CoCo3FPGA yet, I will
> explain some of the features and my thoughts.
>
> As I have already mentioned, I have no capabilities to adapt floppy
> drives into the system. To overcome this limitation, I have modified
> Tandy's Disk Basic to read and write sectors over a serial port to files
> located on a Windows based computer. The serial transfer runs at 115200
> baud. Disk accesses are faster using this method over the original CoCo
> floppy. The Windows computer mounts disk images and serves them up. I
> setup 4 normal sized disks for DECB and up to 5 drives for NitrOS-9,
> i.e. 2 HDD and 3 floppies.
>
> The FPGA that I am using comes with enough block (built into the FPGA)
> RAM to hold the original CoCo3 ROM and the Disk BASIC ROM. I have set
> the Disk BASIC ROM to appear to be in slot 4 of a MPI.
>
> The FPGA board comes with 1M of static RAM. In DECB, you get the full
> 512K of memory. DECB does not have the native support for more than
> that. I have not tried to extend DECB to allow the full use, and I do
> not really see a reason for doing so. What I have done is use the top
> 64K of the extra 512K for two additional "ROMs" that appear to be
> located in slots 2 and 3 in the MPI. The final slot 1 in the MPI is
> empty so I can boot without a ROM if I want to. The board includes 8 two
> position switches and I use two of them to choose the MPI slot. Of
> course you can change the slot selection in software in the normal
> manner. I will need to write a simple program to load the RAM into the
> two ROM slots. In NitrOS-9, you get the full 1M of RAM.
>
> I have added the sound capabilities of the CoCo3. This requires some
> external circuitry. I have used an R-2R DAC in the past and was not
> satisfied with the capabilities; especially at increased CPU speeds. So
> I am converting the 6 bit digital to a pulse width modulated pulse
> stream with 64 different pulse widths. This pulse stream runs fast
> enough where a simple low pass filter should be able to convert it to
> audio. This filter is the additional circuitry needed. I will be
> building prototype circuitry soon for testing.
>
> I am sorry to say, I have no plans to support the standard CoCo
> joysticks. This joystick uses a DAC to sense the position of the
> joystick. As I mentioned in the last paragraph, the response was
> unacceptable in my past tests. What I am planning is a different type of
> joystick. I have not tested this interface. Using a joystick that has 4
> switches, I will emulate the analog circuitry. Using the value written
> to the DAC and the inputs from the 4 switches, the comparator output can
> be read by the software. The different type of joystick will be software
> compatible with the original joystick, but with only three positions
> vertical, up, middle, and down, and three positions horizontal, right,
> middle, and left. I will have a separate serial mouse interface to use
> with NitrOS-9. The hires joystick interface is completely out.
>
> I also need to explain my stance on commercialization. I am not against
> someone developing an adapter board that plugs into this development
> board to give more capabilities. Or even a new board that includes
> everything a hobbyist / student needs. I would be glad to work on
> development with someone, I have a few expansion ideas myself. I can
> easily see additional storage options like IDE / Compact Flash. Or even
> something like a full analog joystick interface. I believe a prototyping
> area and a CoCo compatible ROM slot is mandatory. What I would prefer
> not to happen is someone package this system up for mass market
> consumption similar to the $25 arcade games based on the Commodore 64
> platform that you see at Wal-Mart.
>
> Oh yea, one other thing. With the help of John Kent, the creator of the
> 6809 core I am using and System09, the CoCo3FPGA is now running at
> approximately 16 MHz. But I still have some testing to do to make sure
> it is reliable.
>
> Gary
>
>
>
>
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