Data Available Output (Dav) - IDTECH SecureHead User Manual

SecureHead SPI Interface with FPC User Manual

3.5. Data Available Output (DAV)

The DAV signal is low where there is no data to be transmitted. When the DAV signal is high, it
indicates that there is data available for output. The host and then sends out the clock signal to read the
data. After all the data is transmitted, the device would set the DAV signal low again.
The signal can be used for the host to determine if the device has data ready to transmit. However, the
signal should be ignored right after (1 second maximum) the power cycle or reset as it would be in an
indeterminate state.
In the case when the DAV signal is not used, the host would need to poll the device periodically to
determine if it has data to transmit. The host needs to toggle SCL to get card data from MISO. The first
non-IDLE byte indicates the start of valid card data. IDLE is FF. For more details, please refer to the
communication protocol section of this document.
The last signal shown in the below graph is the DAV signal:
After the command is received and the response is ready, the DAV would be set to high for the host to
receive response. After the response is received, the DAV would be low, indicating there is no more
data to be transmitted.
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