COA asynchronous data transfer
- 1. COMPUTER ORGANIZATION & ARCHITECTURE Name : Mitali Maniyar En.No.:150410107048 Class : SY CE-1 Dept. : Computer
- 2. ASYNCHRONOUS DATA TRANSFER • In a computer system, CPU and an I/O interface are designed independently of each other. • When internal timing in each unit is independent from the other and when registers in interface and registers of CPU uses its own private clock. • In that case the two units are said to be asynchronous to each other. CPU and I/O device must coordinate for data transfers. 2
- 3. • In asynchronous the transmission of data is generally without the use of an external clock signal, where data can be transmitted intermittently rather than in a steady stream. • The most significant aspect of asynchronous communications is that data is not transmitted at regular intervals, thus making possible variable bit rate. • And that the transmitter and receiver clock generators do not have to be exactly synchronized all the time. • Hence we need a start and stop signal to send and receive data.
- 4. METHODS USED IN ASYNCHRONOUS DATA TRANSFER • Strobe Control: This is one way of transfer i.e. by means of strobe pulse supplied by one of the units to indicate to the other unit when the transfer has to occur. • Handshaking: This method is used to accompany each data item being transferred with a control signal that indicates the presence of data in the bus. The unit receiving the data item responds with another control signal to acknowledge receipt of the data. 4
- 5. STROBE CONTROL • Strobe control method of data transfer uses a single control signal for each transfer. The strobe may be activated by either the source unit or the destination unit. • Source Initiated Strobe • Destination Initiated Strobe 5 Source Unit Destination Unit Data bus Strobe
- 6. SOURCE INITIATED STROBE • The data bus carries the binary information from source unit to the destination unit as shown below. • The strobe is a single line that informs the destination unit when a valid data word is available in the bus. Valid dataData Strobe Timing diagram
- 7. SOURCE INITIATED STROBE The source unit first places the data on the bus. After a brief delay to ensure that the data settle to a steady value, the source activities the strobe pulse. The information of the data bus and the strobe signal remain in the active state for a sufficient time period to allow the destination unit to receive the data. The source removes the data from the bus for a brief period of time after it disables its strobe pulse.
- 8. DESTINATION INITIATED STROBE First, the destination unit activates the strobe pulse, informing the source to provide the data. The source unit responds by placing the requested binary information on the unit to accept it. The data must be valid and remain in the bus long enough for the destination unit to accept it. The falling edge of the strobe pulse can be used again to trigger a destination register. The destination unit then disables the strobe. The source removes the data from the bus after a predetermined time interval.
- 9. Source unit Destination unit Data bus Strobe Data Strobe Valid data Source-Initiated Strobe for Data Transfer Source unit Destination unit Data bus Strobe Data Strobe Valid data Block Diagram Destination-Initiated Strobe for Data Transfer Timing Diagram Block Diagram Timing Diagram