10 Questions
What type of control method does asynchronous data transfer using strobe control employ?
Strobe control
In asynchronous data transfer using strobe control, who can activate the strobe?
Source or destination unit
What informs the destination unit in asynchronous data transfer when a valid data word is available on the data bus?
Strobe signal
What does the destination unit typically use to transfer the contents of the data bus into one of its internal registers?
Falling edge of the strobe pulse
What is a disadvantage of the strobe method in asynchronous data transfer?
Source unit does not know if the destination unit received the data item
When does the source unit place the data on the data bus in an asynchronous data transfer using strobe control?
First
What does the source unit do after it disables its Handshaking in asynchronous data transfer?
Removes data from the bus after a brief period
What does a sufficient time period allow in asynchronous data transfer using strobe control?
Destination unit to receive the data
What happens if the source unit initiates a transfer using strobe method and it has no way of knowing whether it succeeded or not?
The source has no way of knowing if the destination received the data
What is often used by destination units to store incoming data temporarily in asynchronous data transfer using strobe?
Internal registers
Study Notes
I/O Interface Unit
- The I/O interface unit communicates directly with the I/O device attached to it.
- The unit consists of four registers that communicate directly with the I/O device.
- Data can be transferred into either Port A or Port B.
Asynchronous Data Transfer
- In asynchronous data transfer, two units, such as a CPU and an I/O interface, operate independently with their own private clocks.
- The internal timing in each unit is independent of the other, and the two units are said to be asynchronous to each other.
Asynchronous Data Transfer Techniques
- Two common techniques used in asynchronous data transfer are strobe control and handshaking.
Strobe Control
- In strobe control, a single control line is used to time each transfer.
- The strobe may be activated by either the source or the destination unit.
- The strobe pulse informs the destination unit when a valid data word is available in the bus.
- The source unit first places the data on the data bus, then activates the strobe pulse.
- The destination unit uses the falling edge of the strobe pulse to transfer the contents of the data bus into one of its internal registers.
Handshaking
- Handshaking is a two-way communication method that ensures the receipt of data.
- Each data item being transferred is accompanied by 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.
Test your knowledge on I/O interface unit, control lines, and data transfer between devices. Learn about the communication registers and the operation of input and output devices connected to the interface.
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