Firstly, the primary asks (poll) the first secondary device, if it responds with the NACK (Negative Acknowledgement) means that it has nothing to send.When a primary device wants to receive the data, then it asks each device whether it has anything to send.The Poll mode is used when the primary device wants to receive some data from the secondary device.Once the data has been transmitted, the secondary sends an acknowledgement specifies that the data has been received.
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