5. What is asynchronous data transfer It is a data transfer method which is used when the speed of IO device does not match with the speed of the microprocessor. Asynchronous data transfer is also called as Handshaking. 6. What are the functional types used in control words of ab The control words of A are divided into two functional types Mode Instruction control word Command Instruction control word Mode Instruction control word - This defines the general operational characteristics of A. Command Instruction control word - The command instruction controls the actual operations of the selected format like enable transmit/receiver, error reset and modem control.