1.2.1 Data Structures
The acquisition module implements all functionality required for making relative measurements of sensor capacitance. This is the only module uniquely built for an individual device, as it must access and control the pins used for touch sensor implementation.
As devices have different hardware features available, different configuration options are available on each device. For the most efficient use of system resources – ROM and RAM – different sensor configuration structures are required.
However, where the same variable name is used within the structure, the functionality controlled by that variable is identical. Any dependent function may utilize a reference to the variable, and NOT rely on a reference to the structure and pointer arithmetic.
Acquisition Group Configuration
A reference by a pointer to
‘&ptc_qtlib_acq_gen1.freq_option_select’ will always point
to the correct memory location, regardless of the device. However, any
implementation based on pointer arithmetic will require re-factoring if code is to
be re-used from one device for another.
| Parameter | Size | Range/Options | Usage |
|---|---|---|---|
num_sensor_nodes | 16-bit | 0 to 65535 | The number of sensor nodes configured in the group |
acq_sensor_type | 8-bit |
NODE_MUTUAL | Defines the measurement method applied to this group of nodes |
calib_option_select | 1 byte | Bits 3:0 Calibration type:
CAL_AUTO_TUNE_CSD* | The calibration type selects which parameter should be automatically tuned for optimal charge transfer |
Bits 7:4 Calibration target:
CAL_CHRG_5TAU | The calibration target applies a limit to the charge transfer loss allowed, where a higher setting of a target ensures a greater proportion of full charge is transferred | ||
freq_option_select | 1 byte |
FREQ_SEL_SPREAD |
FREQ_SEL_SPREAD varies this delay from 0 to 15 in a
sawtooth manner during the oversampling set. |
PTC_interrupt_priority** | 1 byte | 1 to 3 | Interrupt priority level for the PTC. Applicable for all Arm® Device’s except SAME5x |
| 1 byte | 1 to 7 | Applicable for Arm® SAME5x | |
wakeup_exp* | 1 byte | 0 to15 | The Wake-up Exponent is the exponent for the power of 2 which represents the wake-up count in PTC core clocks |
|
Note: * - Not
available on all devices.
** - Applicable for Arm® Cortex devices only. | |||
Node Configuration
Similarly, node configuration structures vary depending on which device is used.
- Number of X lines
- Number of Y lines
- Feature availability
| Parameter | Size | Range/Options | Usage |
|---|---|---|---|
node_xmask |
1/2/4/8 bytes | (Bit field) | Set the bit(s) at location(s) corresponding to X line number(s). Example: X0 only =
X0 and X2 =
1 byte is used for devices with up to 8 “X” lines. 2 bytes, 4 bytes, 8 bytes are used for devices up to 16, 32 and 46* “X” lines, respectively.Note:
*Can support up to 64 X lines. |
node_ymask |
1/2/4/8 bytes | (Bit field) | Set the bit(s) at location(s) corresponding to Y line number(s). Example: Y5 only =
Y1, Y2 and Y7 =
1 byte is used for devices with up to 8 “Y” lines 2 bytes, 4 bytes, 8 bytes are used for devices up to 16, 32, and 46* “Y” lines, respectively.Note:
*Can support up to 64 Y lines. |
node_csd* | 1 byte | 0 to 255 | The number of delay cycles to ensure charging of sensor node capacitances. Applicable for AVR® ATmega324PB,ATmega324PB, Arm® SAML10/L11/L22,SAMC20/C21,PIC32CM_LE/LS,PIC32CK_SG/GC family only. |
| 1 byte | 0 o 31 | Applicable for AVR® ATtiny family only. | |
| 1 byte | 0 to 63 | Applicable for ARM ® SAMLD51/E51/E53/E54 family only. | |
| 1 byte | 0 to 127 | Applicable for AVR® AVR-DA family only. | |
node_rsel_prsc | 1 byte | Bits 7:4 = RSEL
RSEL_VAL_200* |
Internal Y line series resistor selection. * May not be available for all devices. SAM E5x, SAM D5x: 3 kΩ, 6 kΩ, 75 kΩ, 200 kΩ SAM L22: 75 kΩ, 200 kΩ AVR-DA: 70 kΩ, 80 kΩ, 120 kΩ, 200 kΩ |
|
Bits 3:0 = PRSC
|
Clock Prescaler The acquisition clock is derived and scaled from CPU clock for AVR® devices. *May not be available for all devices. SAM E5x, SAM D5x, ATtiny: 16 kΩ, 32 kΩ, 64 kΩ, 128 kΩ AVR-DA: 6, 12, 14 ** **The numbers correspond to the prescaler value. | ||
node_gain | 1 byte | Bits 7:4 = Analog Gain
GAIN_16 | Analog Gain Setting Integration capacitor adjusted to control integrator gain. |
Bits 3:0 = Digital Gain
GAIN_16 |
Digital Gain Setting The accumulated sum is scaled to digital gain. | ||
node_oversampling | 1 byte |
FILTER_LEVEL_1024* | The number of samples to accumulate for each measurement. Note: Oversampling must be configured to be greater than or equal to digital gain for correct operation. (Higher filter level values > 64 are available only on Arm® SAM E54 family only.) |
|
Note: * - Not
available on all devices.
| |||
qtm_cvd_acq_dspic33ck_device_config_t| Parameter | Size | Range/Options | Usage |
|---|---|---|---|
clk_src | 1 byte |
| Selects the ADC clock source |
clk_freq | 4 byte | Clock frequency based on the clk_src
selection | frequency (Hz) of the clock source selected for touch timing |
ext_clk_freq | 4 byte | External clock Frequency | External clock frequency(Hz)when using primary Oscillator with PLL |
device_id | 1 byte |
| Device selection |