IDTECH SecureHead SPI User Manual page 14

When the user swipes a card, no delay is required. Following is the waveform for MSR output:
3.7. Voltage Input and Ground
The VIN signal is the power input for the device and has an operating range of 3.0 to 3.6 volts DC. The
GND signal is logic ground. The head case GND signal is chassis ground, which is connected to the
head case. For optimum ESD protection, this signal should be connected to earth ground.
3.8. Communication
When the host has a frame to send, it pulls the NCS line low, waits 1 millisecond, then clocks it out.
When the device has a frame to send, it raises its data available (DAV) signal and waits for the host to
pull the NCS line low, then clock in the frame. The host normally clocks out IDLE characters to clock in
a frame from the device. Because the device typically loads its one transmit buffer with IDLE byte
when it has nothing to transmit, the first byte clocked out from the device after the DAV signal is
asserted could be IDLE instead of a valid byte. If this is the case, simply discard this byte.
To detect whether the device has a frame to send, the host can either monitor the DAV signal or,
optionally, periodically clock in up to two bytes from the device to see if the device has sent a valid
data. Up to two bytes should be clocked in instead of just one because the first byte could be an IDLE
byte that was loaded into the device's transmit buffers before the device had anything to send. The
host should look at each byte it clocks in to see if it is a valid byte. If a valid byte is found, then the
subsequent bytes will contain the frame.
ID TECH SecureHead SPI with TMIV User Manual
Page | 14