Cyberun: Routine at 39875

39875: Read Keyboard Port

Reads a row of keys, or all of them at once. The bits of the result that are set are the keys that are pressed.

Input
A	Row selector (the high byte of the port address)

Output
A	Keys pressed in the bottom five bits
F	The zero flag is set if no key is pressed

ReadKeyboardPort

39875

OUT (253),A

Output the selector to a port (this has no other effect).

39877

IN A,(254)

Read the row selected by A.

39879

CPL

Invert the bits.

39880

AND %00011111

Keep the five bits for the keys.

39882

RET

Return.

View the equivalent code in;