1. Types of format of data transfer
The format of data transfer are
synchronous and
asynchronous .

2. Synchronous format of data transfer
The transmitter and receiver are synchronized with the same clock – used in high speed data transmission.

3. Asynchronous format of data transfer
Data transmission at irregular intervals of time - used for low speed data transmission.

4. Types of mode of data transfer
The types of mode of data transfer are
parallel mode,
Serial mode .

5. Parallel mode of data transfer
In parallel mode the entire word (8/16 bits) is transferred simultaneously over equal number parallel data lines.

6. Serial mode of data transfer
In serial mode data are transferred (one bit at a time) bit by bit over a single line between peripheral and MPU.

7. Types of IO The types of IO are peripheral mapped IO ,
Memory mapped IO .

8. Peripheral mapped IO
In peripheral mapped IO the peripheral is mapped into much smaller IO address space of MPU and identified with an 8 bit address (port number).
Instruction used are
IN port_address8,
OUT port_address8.

9. Memory mapped I/O
In Memory mapped IO the peripheral is mapped into the memory address space of MPU and identified with 16 bit address.
Memory related instructions used are:
STA mem_address16,
LDA mem_address16,
MOV R, M
STAX reg_pair  

10. Types of microprocessor controlled data transfer
The microprocessor controlled data transfer consists of
unconditional data transfer ,
data transfer with polling (status check),
data transfer with interrupt,
data transfer with handshake signal.

11. Unconditional data transfer
The MPU assumes that the peripheral is always available. MPU enables ports, transfers data and goes on execution of next instruction.

12. Data transfer with polling (status check)
The MPU is kept in a loop to check whether data is available.

13. Diagram of Polled input / output

14. Data transfer with interrupt
When a peripheral is ready to transfer data, it sends an interrupt signal to the MPU. The MPU stops execution of the program, accept data from the peripheral and then returns to the program.

15. Diagram of interrupt driven input / output

16. Data transfer with handshake signal
Signals are exchanged between the fast responding MPU and slow responding peripherals prior to actual data transfer. These signals are called handshake signal.

17. Purpose of handshake signal
The function of the handshake signal is to
ensure the readiness of peripherals
and
to synchronize the timing of data transfer.