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AT42QT1111-MU Datasheet(PDF) 11 Page - ATMEL Corporation |
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AT42QT1111-MU Datasheet(HTML) 11 Page - ATMEL Corporation |
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11 / 50 page  11 9571A–AT42–02/10 AT42QT1111-MU/AT42QT1111-AU 4.1.3 CRC Bytes 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 A. 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. 4.1.4 SPI Commands There are three types of communication between the SPI master and the QT1111: • Control commands (see Section 5 on page 22) – To send control instructions to the QT1111 • Report requests (see Section 6 on page 24) – To reading status information from the QT1111 • 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 QT1111. 4.1.4.1 Control Commands 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. Sleep Command – CRC Disabled Host (Sends on MOSI) Device (Responds on MISO) Simultaneous Transmission Command: 0x05 Response: 0x55 ( Idle” Fresh Command) “ – |
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