Touchscreen Mode 01—Auto - Freescale Semiconductor MCF52277 Reference Manual

Touchscreen Controller/Analog-to-Digital Converter
22.5.3 Touchscreen Mode 01—Auto
Touchscreen mode 01 auto is recommended for applications that require continuous input (such as a
drawing), higher coordinate resolution (by averaging the measurement), or touch with cancel capability
(by detecting that the pen-up point is different than the pen-down point).
The operation in this mode is also highly automatic. After the MCU completes configuration, the handling
can be interrupt driven to save processing load on the MCU. The processor needs to set ASPE when the
pen-down interrupt is detected and then upload the measurement results during the FIFO watermark
interrupt service routine.
Figure 22-13 and Figure 22-14
MODE = 01 and AUTO = 1. The following example assumes MIDLECNT ≠ 0, RIDLECNT ≠ 0,
PENE = 1, AZE = 1.
BIACTRL
Pen
SELREFP
SELREFN
det ect i on
SELINP
a
PENDOWN_IRQ
ASPE
FIFO_WM_IRQ
BIACTRL
SELREFP
AZX
SELREFN
SELINP
FIFO_WM_IRQ
PENUP_IRQ
ASPE
a) When ASP configuration is complete, the ASP parks on pen detection state.
b) Pen-down event is detected and the pen-down interrupt occurs.
c) MCU responds to the interrupt and disables the pen-down interrupt. It is recommended to clear
the FIFO in this step.
d) MCU sets ASPE to initiate the measurement operation.
e) ASP is begins the continuous measurement.
f) FIFO watermark interrupt occurs when one round of conversions is complete. For this
example, the watermark level is 4.
g) MCU uploads the results of one round of conversions, which clears the FIFO watermark
interrupt.
h) Step f and g occur repeatedly.
i) FIFO watermark interrupt occurs for the last round of conversions.
22-20
illustrate a typical operation sequence when TSE = 1, CALA = 0,
Pen
AZX X m easur e
det ect i on
e
b c
d
Figure 22-13. Mode 01 Auto, Part 1
X m easur e AZY Y m easur e
Figure 22-14. Mode 01 Auto, Part 2
MCF52277 Reference Manual, Rev. 1
M easur em ent
AZY Y m easur e
I DEL
f
Round Pen
AZX
I DLE det ect i on
i j
k
l
Round Pen
AZX X m easur e
I DLE det ect i on
g
Pen Pen
det ect i on det ect i on det ect i on
n
m
Freescale Semiconductor
Pen