Untitled

// ps2_valid   port20 
// ps2_ack     port21
// ps2_pressed port22
// ps2_ascii   port23

ps2_wait	in  21 ps2_ack     // read ps2_ack
ps2_press   in  22 ps2_pressed // read ps2_pressed

            out 20 ps2_zero    // set valid to 0

            bne ps2_press ps2_pressed ps2_one // loop if pressed != 1
            out 20 ps2_one     // set valid to 1

            bne ps2_wait ps2_ack ps2_one // loop if ack != 1
            out 20 ps2_zero    // set valid to 0

ps2_ack     .data 0
ps2_pressed .data 0

ps2_zero	.data	0
ps2_one	.data	1