User Manual

9570H–AT42–02/10

AT42QT1110-MZ/AT42QT1110-AZ

4.1.3 CRC Bytes

If enabled, a CRC checking procedure is implemented on all communications between the SPI

master and the QT1110. 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 QT1110 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 A.

When the QT1110 is expecting a CRC byte, it returns (on MISO) the calculated CRC byte which

it expects to receive. This is sent simultaneously with the QT1110 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 QT1110 is also be followed by a CRC byte, allowing the master to

confirm the integrity of the data transmission.

4.1.4 SPI Commands

There are three types of communication between the SPI master and the QT1110:

• Control commands (see Section 5 on page 22)

– To send control instructions to the QT1110

• Report requests (see Section 6 on page 24)

– To reading status information from the QT1110

• Setup commands (see Section 7 on page 28)

– To set configuration options (“Set” instructions)

– To read configuration options (“Get” instructions)

Additionally the “Null” command (0x00) is transmitted by the host device as it is receiving data

from the QT1110.

4.1.4.1 Control Commands

A control command is an instruction sent to the QT1110 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. Sleep Command – CRC Disabled

Host (Sends on MOSI)

Device (Responds on MISO)

Simultaneous

Transmission

Command: 0x05

Response: 0x55 ( Idle” Fresh Command)“ –