synchronous and asynchronous input\output operation

1. DATA TRANSFER SCHEME
There are two types of data transfer scheme:
1. Synchronous
2. Asynchronous

2. Synchronous input / output transfer
• Common clock signal is used.
• At time t₀ the processor places the device
address on the address lines of system bus.
• During time t₀-t₁, address device gets the
address & it recognize that an input operation
is requested.

3. CONTINUED…
• At time t₁, address device places its data on
the data bus. At the end of the bus cycle
i.e, at t₂ the processor reads the data lines &
loads the data from data bus into its input
buffer.
• For output processor places the output data
on data line.
• At t₁ - Device reads the data line and load
data into its data buffer.
• At t₂ - Output have been received by the IO
device and the cycle ends.

4. ASYNCHRONOUS INPUT/OUTPUT
TRANSFER
• The clock line replaced by two control signal ready
and accept.
• For input operation, processor places the address
& sets the control lines to perform the input
operation.
• Ready line activated – Addressed device ready to
accept data.
• Addressed device place data on data accept line
activated.
• Processor load data on input buffer.

5. CONTINUED…
For output operation:
• Processor places the address, data and sets the
control line to perform the output operation.
• It then indicates the addressed device that it
has send data by activating Ready signal.
• The addressed device reads data into its input
buffer when it receive ready signal. It then
indicates that it has done so by the Accept
signal.