ID TECH SecureHead SPI with TMIV User Manual
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After the command is received and the response is ready, the DAV would be set too
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.
A
fter receiving a command,
typically within less than
20ms, response is ready and DAV set
to
high
. For some specific commands, the delay may be longer.
After the last byte of response is sent, the DAV is pulled low. If user polls DAV status to check
whether there are data available, we suggest using 100
μ
s polling interval and throw away any data
when DAV is low.
3.6.
Chip Select
SPI interface allows connecting several SPI devices while master selects each of them with NCS (Chip
Select, Active Low). The device will only respond to SPCK and MOSI signals after an NCS is pulled low.
For the first byte of each command sent to SecureHead, NCS needs to be pulled low for 1 millisecond
before the clock line. Because SecureHead is always in deep sleep mode when in idle status, this 1
millisecond delay is required to allow SecureHead wake up from sleep mode.
