AT77C104B_08 Datasheet, PDF (25/46 Pages) ATMEL Corporation – FingerChip Thermal Fingerprint Sweep Sensor, Hardware Based, Navigation and Click Function, SPI Interface

AT77C104B
12. Control Interface (Slow SPI)
This interface controls the sensor’s internal registers. The protocol enables reading and writing
of these registers.
The master (host) initiates transfers to the slave (sensor). The sensor can only use its interrupt
pin to communicate with the host. When the host is interrupted, it must read the status register
before continuing operation.
The word length of the transferred data is fixed to 8 bits. The Most Significant Bit (MSB) is sent
first.
12.1 Communication Protocol
Accesses to the host are structured in packets of words. The first word is the command and the
other words are the data.
The b7 bit is used to differentiate the command and data. When the word is a command, b7 is
high ('1') and when the word is a piece of data, b7 is low ('0').
The following protocol is used:
12.1.0.1
b7
1
Command Format
The host indicates to the sensor if it wants to read or write into a register and indicates the regis-
ter’s address.
b6
b5
b4
b3
b2
b1
b0
Read
(1)/Write (0)
Address (b3) Address (b2) Address (b1) Address (b0)
x
x
12.1.0.2
Data Format (Writing into Register)
If writing into a register, the host transmits the data.
b7
b6
b5
b4
b3
b2
b1
b0
0
Data (b6)
Data (b5)
Data (b4)
Data (b3)
Data (b2)
Data (b1)
Data (b0)
12.1.0.3
Data Format (Reading of Register)
If reading a register, the host transmits one or several packets of data and data is shifted in from
the sensor. The host transmits dummy words with the data format (b7 is low ['0’]). If reading the
navigation or pixelclick registers, the host transmits three packets of data to read the three
registers.
b7
b6
b5
b4
b3
b2
b1
b0
0
x
x
x
x
x
x
x
Note: The host cannot communicate with the sensor without receiving data from it. Useless data is ignored by the host.
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