SKC - простой контроллер PC/AT-клавиатуры на ATmega88

[VELESOFT]

After press ZX key combined with shift (extend mode, cursor keys, caps lock, etc..) you must:
1) active only shift in time min. 1/50 sec
2) active next key parallel with shift

After release this combined ZX key:
1) release key only (shift is active)
2) after time min. 1/50 sec also release shift

This is function of original multilayer ZX membrane.
ZX BASIC also work better with this. KEY routine need shift before active key.