Functional Description
12.3 Functional Description
Before enabling the TSC_ADC_SS module, the user must first program the Step Configuration registers in
order to configure a channel input to be sampled. There are 16 programmable Step Configuration
registers which are used by the sequencer to control which switches to turn on or off (inputs to the AFE),
which channel to sample, and which mode to use (HW triggered or SW enabled, one-shot or continuous,
averaging, where to save the FIFO data, etc).
12.3.1 HW Synchronized or SW Channels
The user can control the start behavior of each channel input by deciding if a channel should be sampled
immediately (SW enabled) after it is enabled, or if the channel should wait for a HW event to occur first ( a
HW event must either be mapped to the touch screen PEN event or mapped to the HW event input signal,
but not both). Each channel input can be configured independently via the Step Configuration register.
12.3.2 Open Delay and Sample Delay
The user can program the delay between driving the inputs to the AFE and the time to send the start of
conversion signal. This delay can be used to allow the voltages to stabilize on the touch screen panel
before sampling. This delay is called “open delay” and can also be programmed to zero. The user also
has control of the sampling time (width of the start of conversion signal) to the AFE which is called the
“sample delay”. Each channel input is configured independently via the Step Delay register.
12.3.3 Averaging of Samples (1, 2, 4, 8, and 16)
Each channel input has the capability to average the sampled data. The valid averaging options are 1 (no
average), 2, 4, 8, and 16. If averaging is turned on, then the channel is immediately sampled again (up to
16 times) and final averaged sample data is stored in the FIFO. Each channel input can be independently
configured via the Step Configuration registers.
12.3.4 One-Shot (Single) or Continuous Mode
When the sequencer finishes cycling through all the enabled steps, the user can decide if the sequencer
should stop (one-shot), or loop back and schedule a the step again (continuous).
If one-shot mode is selected, the sequencer will take care of disabling the step enable bit after the
conversion. If continuous mode is selected, it is the software’s responsibility to turn off the step enable bit.
12.3.5 Interrupts
The following interrupts are supported via enable bits and are maskable.
The HW Pen (Touch) interrupt is generated when the user presses the touchscreen. This can only occur if
the AFE is configured properly (i.e., one of the Pen Ctrl bits must be enabled, and also the correct setting
for a path to ground in the StepConfig Registers). Although the HW Pen interrupt can be disabled by the
SW, the event will still trigger the sequencer to start if the step is configured as a HW synchronized event.
The HW Pen interrupt is an asynchronous event and can be used even if the TSC_ADC_SS clocks are
disabled. The HW Pen interrupt can be used to as a wakeup source.
An END_OF_SEQUENCE interrupt is generated after the sequencer finishes servicing the last enabled
step.
A PEN_UP interrupt generates only if the HW steps are used and the Charge step must be enabled. If a
HW Pen event caused the HW steps to be scheduled and no HW Pen (touch) is active after the
sequencer finished servicing the charge step, then a PEN_UP interrupt is generated. To detect PEN_UP
interrupts, the charge step must share the same configuration as the idle step.
1026
Touchscreen Controller
SPRUH73H – October 2011 – Revised April 2013
Copyright © 2011–2013, Texas Instruments Incorporated