[Coco] CoCo <--> Raspberry Pi

[John E. Malmberg]

Thunderbird has decided that it will not show me Gene Heskett's reply to 
this message.

On 3/9/2020 11:57 PM, James Ross wrote:
> Of interest as well was the CoCo <--> Raspberry Pi project discussed
> on the latest CoCoTalk – I caught a good 30 minutes of that
> conversation on the day.  I went back and listened to that whole
> section, it starts around the 3 hr mark ...)  Quite interesting,
> kudos to the dude that is experimenting w/ that.

Did not know about that.  I am several thousand messages behind on this 
forum, and having to switch to gmain.io reset all messages to be unread.
> I wonder how fast you can feed data to the CoCo through the keyboard
> input, if bypassing the ROM and talking directly to the port in
> assembler?

You mean by a 6809/6309 program that is polling the ports and with a 
computer attached instead of a ke?  I would have to look at the I/O 
timing for the chipset, but you can probably transfer at about 1/10 of 
clock speed depending on efficiently that you wrote the code.

> I imagine the Raspberry Pi (possibly only the newer ones 3, 4?) are
> fast enough to R/W directly to cartridge slot at full double speed
> 1.79MHz? ...

I do not think that is the best connection method.  There is not enough 
I/O pins so that extra selection logic is needed.

And most of the IO expanders that I have found for the Pi are also too slow.

I am currently looking at a https://www.sparkfun.com/products/9713 as 
something to connect to the 40 pin and other I/O ports, or just to 
emulate a COCO altogether.

That device has enough I/O to connect in, and it can connect to the Pi 
via either SIO or USB.

I am not sure about any buffering / level conversion.  What I like about 
that device is it is breadboard ready to go.

I am only just now starting to go through my COCO stuff to figure out 
what I have that is still functional and what can be repaired.

Regards,
-John