Filter
Top Products
CLCD Display and Adaptor Board
ARM DUI 0224F Copyright © 2003-2007 ARM Limited. All rights reserved. C-13
C.3.2 Touchscreen controller programmer’s interface
The LCD Touch Screen Controller Interface (TSCI) is based on a TSC2200 PDA
analogue interface circuit. Use the ARM926EJ-S PXP Development Chip SSP interface
to configure and read the touch screen. For information on the touch screen registers,
see the TSC2200 data sheet.
The TSC2200 also incorporates a sixteen key keypad interface and two 12bit analogue
inputs that are available through the LCD expansion header J13. With the 3.8 inch
Sanyo and 2.2 inch Epson build options, six keypad push buttons are mounted on the
LCD board.
SSP and TSCI Configuration
The SSP interface is controlled by the SSP PrimeCell and the SSP TSCI chip select is
enabled through SYS_CLCD TSnSS signal. Configuration of the SSP to TSCI interface
requires the data format, phase, size, and clock to be set correctly. Example
configuration code is given in the selftest (TSCI) software on the CD, a code fragment
from this is shown in Example C-1.
Example C-1 SSP to TSCI interface setup
// Set serial clock rate (/3), Phase (SPH), Format (MOT), data size (16bit)
*SSPCR0 = SSPCR0_SCR_DFLT | SSPCR0_SPH | SSPCR0_FRF_MOT | SSPCR0_DSS_16;
// Clock prescale register (/8), with SCR gives 0.78MHz SCLK: 24MHz / 8*(1+3)
*SSPCPSR = SSPCPSR_DFLT;
// Enable serial port operation
*SSPCR1 = SSPCR1_SSE;
The TSC2200 TSCI controller registers must be configured through the SSP interface
to enable correct touch screen operation.
After the TSCI is configured, conversion of touch screen X/Y values is fully automated
by the TSCI controller and the application code simply reads the converted values. Use
either the pen down flag in the touch screen controller interface or SIC interrupt 8 to
detect the current pen state. The pseudo code in Example C-2 on page C-14 shows the
sequence for configuring and reading the TSCI interface.
Read and write functions are used in the selftest code to transfer data to and from the
TSCI registers TSCI_RTSC and TSCI_WTSC. The selftest example configures the
TSCI for 12bit operation and 16 data averages with minimum precharge and sense
times. This gives high accuracy and fast reading of the current pen position.