ID TECH SecureHead SPI with TMIV User Manual
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3.4.
Master Output, Slave Input (MOSI)
The MOSI signal is the serial data input for the device and serial data output for the host. This signal is
sent from the host (master) to the device (slave). The signal might not be required after some device
parameters such as the device key has been set and saved. Set the signal to be high if it is not being
used.
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 sets 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 a reset, as it would be
in an indeterminate state.
In the case when the DAV signal is not used, the host will 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 in
The following graph shows the command and response for
command. The last signal
shown in the graph is the DAV signal: