[Coco] Altera DE1 - CoCo3FPGA suggestions

[Nick Marentes]

Now that I have had a played with my DE1 board running the current 
version of the CoCo3FPGA, I would be completely out of character if I 
didn’t have a list of suggestions I see as possible improvements to the 
design. :)

Here is my Altera DE1 -CoCo3FPGA wishlist…

CPU SPEED

Currently, the CoCo3FPGA runs at the original CoCo speed of 0.89 Mhz and 
when put in the double clock speed mode (&HFFD9=1) runs at a speed 
dependant on the position of switches 0 & 1 (1.78, 4.17, 12.5 or 25 Mhz).

My suggestion is to do away with all the intermediate speeds and simply 
have 25 Mhz as the high clock speed. Would anyone use anything other 
than the fastest?

I also would redefine the switch definitions and utilize just a single 
switch.

When switch 0 is off, CoCo3FPGA should operate like a normal CoCo3 with 
0.89Mhz in normal clock mode and 1.79Mhz at double clock mode. This is 
for compatibility.

When switch 0 is on, then both clock modes (normal and double) should 
operate at 25Mhz. This makes everything run fast even if they don’t 
activate double clock mode.

I don’t see the need for 2 clock speeds. Everyone will tend to want to 
run it at it’s fastest.

VIDEO SCANLINES

Define the switch made free after the CPU SPEED change to act as a 
Scanlines ON/OFF switch.

Currently, any CoCo3 video mode with a maximum of 225 scanlines is being 
drawn twice to make up the 480 VGA style display. This is knoiwn as Scan 
Doubled. When a new 480 scanline mode is activates, this doubling of 
scanlines is turned off to provide a full res 480 line VGA display.

When switch 1 is on, video for modes 225 scanlines or less should be 
handled with Scan Doubling as it currently is.

When switch 1 is off, video for 225 mode scan lines are drawn as 1 
normal scan line and 1 blank (black) scan line to simulate the scan 
lines of a classic non VGA monitor. This gives a more “authentic” look 
to the display and tends to make games look better.

SERIAL PORTS

The bit banger serial port should be moved to the add-on analogue board 
along with the 2 joystick ports. The on board serial port of the DE1 
should become a second real serial port. This serial port can be used as 
emulating the Deluxe RS-232 Pak port.

SOUND

I would not bother emulating the Orchestra 90 or Sound & Speech Paks. 
Little software uses these anyway. I would be looking at implementing a 
new sound system, maybe leveraging off the CoCo’s DAC mono sound system. 
(NEEDS MORE THOUGHT)

MULTI-PAK

I would do away with the emulation of the multi-pak and have the disk 
controller and Disk Basic support created as a Disk Controller cartridge 
plugged directly into the CoCo.

All extra hardware such as RS-232 and Sound Paks should be built in to 
the new CoCo3FPGA as a single design.

DRIVEWIRE AND SD CARDS

Support the Drivewire protocol via the onboard RS-232 port of the DE1 
board (as it currently is) but also offer saving/loading DSK’s to the SD 
Card. It wouldn’t be so important to run a floppy disk controller 
emulation to allow 100% compatibility with software that provides its 
own disk routines. This sacrifice can be made to simplify the addition 
of being able to use the onboard SD Card. OS-9 won’t be a problem.

I’m not sure but we may not need a FAT file system on the SD Card for 
compatibility of the files on a PC. Instead, we could add files to the 
SD Card from the PC using the Drivewire link.