Programmed I/O Data Transfer scheme of 8085 microprocessor is a simple parallel data transfer scheme. This method of data transfer is generally used in the simple microprocessor systems. It is obvious that where speed is unimportant. This method uses instructions to get the data in or out of the microprocessor.
Programmed I/O Data Transfer scheme can be work on synchronous or asynchronous mode. When the data transfer can be synchronous or asynchronous, it completely depends upon the type and the speed of the I/O devices.
So before go for programmed I/O data transfer, we should know little bit about synchronous and asynchronous type data transfer.
Synchronous type of data transfer
Synchronous type of data transfer can be used when the speed of the I/O devices matches with the speed of the 8085 microprocessor. So we need common clock pulse for established the synchronization between I/O device and microprocessor. This common clock pulse synchronizes the microprocessor and the I/O devices. In synchronous type of data transfer scheme, it has matching of the speed with I/O devices. So it does not have to wait for the availability of the data. As soon as the microprocessor issues a signal, it immediately sends data for the transfer .
The asynchronous type data transfer
The asynchronous data transfer method is used when the speed of the I/O devices is slower than the speed of the microprocessor. Because of the mismatch of the speed, the internal timing of the I/O device is independent from the microprocessor. That is why those two units can said to be asynchronous to each other. The asynchronous data transfer is normally implemented using ‘handshaking’ mode.
Now question is “what is handshaking mode?” In the handshaking mode some signals are exchanged between the I/O device and microprocessor before the data transfer takes place. Now look at the flow chart bellow which can describe the total process step wise.
By this handshaking it has to check the status to the input/output device. Now if it found the device is ready for the data transfer. Then it performs some simple steps to complete the task.
- First step of microprocessor is initiates the I/O device to get ready.
- Then status of the I/O device continuously checked by the microprocessor.
- This process remain continues until the I/O device becomes ready.
- After that microprocessor sends instructions to transfer the data.
Working Process
Now form this bellow figure, we can see that the microprocessor sends a ready signal to I/O device. When the device is ready to accept the data, the I/O device sends an ‘ACK’ (Acknowledge) signal to microprocessor. By sending ACK, it indicating that the I/O device has acknowledged the ‘Ready’ signal. Now finally it is ready for the transfer of data.
Again in bellow figure shows the asynchronous handshaking process to transfer the data from the I/O device to microprocessor. In this case I/O device issues the ready signal to microprocessor indicating that I/O device is ready to send the data to microprocessor. So in response to this signal, the microprocessor send valid data signal to I/O device and then that data put on the data bus for the transfer.
In conclusion, hope this discussion on programmed I/O Data Transfer scheme of 8085 microprocessor helped you to understand the data transfer scheme.
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Data Transfer in 8085 microprocessor.Data Transfer
