[sdiy] Casio CV out retrofitting... ..confusion

[Karl Ekdahl]

Hi list

I'm doing a CV out for a casio, using the common technique of scanning the output from the CPU to the keyboard and reading what comes out of it. The output lines are ACTIVE LOW and goes to eight groups of keys, each key outputting to a shared six-line databus (i.e all C's and F#s on data line 0, C# and G's on data line 1 etc.) . Now reading the six keys as ACTIVE LOW works just fine, but figuring out which group is active is getting retardedly hard. I was expecting all lines to be HIGH except for the line of the group that was currently scanned, something like 

11111110 
11111101 
11111011 
11110111 
11101111 
11011111 
10111111 
01111111

But i never get this, all i get is a mash-up of 1's and 0's making it impossible to know which group the depressed key belongs to. I wonder if i'm just confused or maybe it's some kind of timing issue? i did this several years ago to an SK-1 and it worked fine.. comments?

Karl


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