[Coco] Where can I find information on using the Cartridge port for I/O ?

[Neil Cherry]

On 12/24/20 4:52 PM, Rick Ulland wrote:
> 
> 
> On 12/24/20 12:47 PM, Neil Cherry wrote:
>> I'll start out simple as I'm sure there's a lot I don't know.
>>
>> I want to build a cartridge with an interface to a USB keyboard using the CH376. What information
>> is available for using the Cartridge port for I/O with ROM on the board. I'll need the board to
>> be read at startup so that it can add the interrupt chain.
>>
>>
>> CH376
>> https://www.mpja.com/download/31813MPSch.pdf
>>
> 
> 
> Most keyboard mods I am familiar with emulate the physical connections of the CoCo keyboard, and are plugged into the keyboard 
> connector. Because...
> 
> The cartridge port doesn’t give you a lot to work with. It was designed for one software ROM select (CTS) and one hardware select 
> (SCS), and includes one return (CART) that ECB/DECB interprets as ‘run the ROM’. Since there will only ever be one, a disk 
> controller with onboard ROM can ask to be auto-executed and lean on these three signals, needs little decoding hardware onboard.
> 
> The MPI can switch between 4 different 1+1 devices, but you can’t effectively manage that from the MPI side, and worse, it switches 
> the CART return to the one & only active device this scheme can handle. OS9 folks physically ‘strap’ all four slot’s CART lines 
> together so any slot can trigger an IRQ poll sequence, but that is both 'hardware hacking' and polling doesn’t exist in DECB anyway 
> - no IRQ for you!

I actually have a better method for interfacing a keyboard to any vintage computer. I found a
method to use a microcontroller (uC) and a 1: ration of transistors to rows and columns. The
uC translates the USB keyboard to the vintage computer map. I just wanted to play a bit with
the CH376 (which can also handle any HID device, such as USB sticks and mice and weird things
like digital I/O and ADC/DAC boards I have). I also plan to attempt this with my Atari 800xl.

 >
 > Sorry to be no help whatsoever.

I learned what it can't do, that's as important as what it can do. I was hoping for a non-
invasive method, but they're not all designed that way.

The tranistor method require I solder a set of single row socket to where the keyboard
ribbon attached. This should allow the original keyboard to still operate.

-- 
Linux Home Automation         Neil Cherry       ncherry at linuxha.com
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Author of:    	Linux Smart Homes For Dummies