IKCH-40 IBM PC/AT Keyboard Interface
You may ask yourself, "Why create an IBM PC/AT Keyboard to USB interface when I can buy one for $5?"
The ones you buy for $5 are junk. (And they obligate you to buy an IBM PC/AT to IBM PS/2 adaptor.)
They're junk because they don't support N-key rollover.
Now, there's a lot of misinformation about N-key rollover, so here's my take.
If I press and hold A, then press and hold B, then press and hold C and so on through D, E, F right up to Z, what should happen?
As far as scanning is concerned, the keyboard should report A, then B, then C, and so on, through Z. If Z is still held, then Z should start to auto-repeat.
This is exactly what the IBM PC/AT keyboard did when installed on an IBM PC/AT computer.
Most of the $5 adaptors that you get give up after two or three keys are pressed together, and just stop emitting keys.