Operational Modes
12.4.1 PenCtrl and PenIRQ
The Pen IRQ can only occur if the correct AFE_Pen_Ctrl bits are high in the CTRL register and if the
correct ground transistor biasing is set in the StepConfig[n] Register. Refer to the application notes for the
correct settings.
If a step is configured as HW-synchronized, the sequencer will override the AFE_Pen_Ctrl bits set by the
software (bits 6:5) once it transitions from the Idlestep. The sequencer will automatically mask the
AFE_Pen_Ctrl bits (override them and turn them off) so that the ADC can get an accurate measurement
from the x and y channels. After the last HW synchronized step, the sequence will go to the Charge step
and the pen override mask is removed and the values set by the software (bits 6:5) will have control. The
HW Pen events will be temporarily ignored during the Charge step (HW will mask any potential glitches
that may occur)
If the sequencer is not using the HW synchronized approach, (all the steps are configured as software
enabled), then it is the software programmer’s responsibility to correctly turn on and off the AFE_Pen_Ctrl
bits to receive the correct measurements from the touchscreen. The software must enable the Charge
step and ignore any potential glitches.
It is also possible to detect the HW Pen event even if all the StepEnable[n] bits are off. By setting the
AFE_Ctrl_Pin bit to 1, and configuring the IdleStep Configuration register to correctly bias the transistor to
ground, the HW_Pen event will be generated. The flowchart for the sequencer is shown in
and an example timing diagram in
.
1030
Touchscreen Controller
SPRUH73H – October 2011 – Revised April 2013
Copyright © 2011–2013, Texas Instruments Incorporated