Rainbow Electronics AT42QT1110-AZ - Manual (Page 18)

18
9570H–AT42–02/10
AT42QT1110-MZ/AT42QT1110-AZ
• Touch mode
– The CHANGE pin is pulled low when one or more keys are in detect. The CHANGE
pin remains low as long as there is a key in detect, regardless of communications.
– The CHANGE pin is released when there are no keys in detect. No host
communications are required to release the CHANGE pin.
4.6 Stand-alone Mode
The QT1110 can operate in a stand-alone mode without the use of the SPI interface. The
settings are loaded from EEPROM and the device operates in 7-key mode using the Detect
outputs.
4.7 Key Modes
4.7.1 11-key Mode
In 11-key mode, the device can sense up to 11 keys. Alternatively, one key can be replaced by
the SYNC line as an external trigger input (see
Section 4.8.2 on page 19 ).
11-key mode is configured by setting the “MODE” bit in the Device Mode setup byte (see
Section 7.4 on page 29 ).
Key acquisition can be triggered in one of two ways: using the internal clock to trigger acquisition
either at a fixed repetition period or in a continuous “free run” mode (see
Section 4.8.1 ), or using
the SYNC pin to provide an external trigger (see Section 4.8.2 on page 19 ),
4.7.2 7-key Mode
In 7-key mode, the detect outputs DETECT0 to DETECT6 become active on pins 22–27 and 30.
These outputs provide configurable PWM signals that indicate when each of the keys is
touched.
7-key mode is configured by clearing the “MODE” bit in the Device Mode setup byte (see
Section 7.4 on page 29 ).
Each DETECT output can be individually configured to output a PWM signal while the matching
key is in detect or out of detect. This signal can be one of nine levels, ranging from low
(PWM = 0 percent) to high (PWM = 100 percent). This allows for the use of an indicating LED.
This is achieved by enabling the appropriate bit in the Key to LED setup byte (see
Section 7.14
on page 35 ), and setting the desired outputs levels or PWMs in setup addresses 9 to 15 (see
Section 7.12 on page 33 ).
4.8 Trigger Modes
4.8.1 Timed Trigger
In 11-key mode, The QT1110 can be configured to use the internal clock as a timed trigger. In
this case, the QT1110 is configured with a cycle period, such that each acquisition cycle starts a
specified length of time after the start of the previous cycle. If the cycle period is set to “0”, each
acquisition cycle starts as soon as the previous one has finished, resulting in the acquisition
cycles running back-to-back in a “free run” mode.
The use of a timed trigger, and the cycle period to be used, is set in the Device Mode setup byte
(see
Section 7.4 on page 29 ).