AT42QT1111MU ATMEL [ATMEL Corporation], AT42QT1111MU Datasheet - Page 11

• Manufacturer Part Number: AT42QT1111MU
• Manufacturer: ATMEL [ATMEL Corporation]

4.1.3
4.1.4
4.1.4.1
9571A–AT42–02/10
CRC Bytes
SPI Commands
Control Commands
If enabled, a CRC checking procedure is implemented on all communications between the SPI
master and the QT1111. In this case, each command or report request sent by the master must
have a byte appended containing the CRC checksum of the data sent. The QT1111 will not
respond to commands until the CRC byte has been received and verified.
Sample C code showing the algorithm for calculating the CRC of the data can be found in
Appendix
When the QT1111 is expecting a CRC byte, it returns (on MISO) the calculated CRC byte which
it expects to receive. This is sent simultaneously with the QT1111 receiving the CRC byte from
the master (that is, during the same byte exchange). This allows both devices to confirm that the
data was sent correctly.
All data returned by the QT1111 is also be followed by a CRC byte, allowing the master to
confirm the integrity of the data transmission.
There are three types of communication between the SPI master and the QT1111:
Additionally the “Null” command (0x00) is transmitted by the host device as it is receiving data
from the QT1111.
A control command is an instruction sent to the QT1111 that controls operations of the device,
and for which no response is required. Examples of control commands are: “Reset”, “Calibrate”,
“Send Setups”.
With the exception of “Send Setups”, control commands normally require a single byte
exchange, unless CRC checking is enabled, in which case a second byte must be transmitted
by the host with the calculated CRC of the command byte.
Figure 4-1.
• Control commands (see
• Report requests (see
• Setup commands (see
– To send control instructions to the QT1111
– To reading status information from the QT1111
– To set configuration options (“Set” instructions)
– To read configuration options (“Get” instructions)
Host (Sends on MOSI)
A.
Sleep Command – CRC Disabled
Section 6 on page
Response: 0x55 ( Idle”
Section 7 on page
Section 5 on page
AT42QT1111-MU/AT42QT1111-AU
Command: 0x05
“
24)
28)
22)
–
Fresh Command)
Device (Responds on MISO)
Simultaneous
Transmission
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