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S3C2440A RISC MICROPROCESSOR ADC AND TOUCH SCREEN INTERFACE
16-3
FUNCTION DESCRIPTIONS
A/D Conversion Time
When the GCLK frequency is 50MHz and the prescaler value is 49, total 10-bit conversion time is as follows.
A/D converter freq. = 50MHz/(49+1) = 1MHz
Conversion time = 1/(1MHz / 5cycles) = 1/200KHz = 5 us
NOTE
This A/D converter was designed to operate at maximum 2.5MHz clock, so the conversion rate can go up to 500 KSPS.
Touch Screen Interface Mode
1. Normal Conversion Mode
Single Conversion Mode is the most likely used for General Purpose ADC Conversion. This mode can be
initialized by setting the ADCCON (ADC Control Register) and completed with a read and a write to the
ADCDAT0 (ADC Data Register 0).
2. Separate X/Y position conversion Mode
Touch Screen Controller can be operated by one of two Conversion Modes. Separate X/Y Position Conversion
Mode is operated as the following way. X-Position Mode writes X-Position Conversion Data to ADCDAT0, so
Touch Screen Interface generates the Interrupt source to Interrupt Controller. Y-Position Mode writes Y-Position
Conversion Data to ADCDAT1, so Touch Screen Interface generates the Interrupt source to Interrupt Controller.
3. Auto(Sequential) X/Y Position Conversion Mode
Auto (Sequential) X/Y Position Conversion Mode is operated as the following. Touch Screen Controller
sequentially converts X-Position and Y-Position that is touched. After Touch controller writes X-measurement
data to ADCDAT0 and writes Y-measurement data to ADCDAT1, Touch Screen Interface is generating Interrupt
source to Interrupt Controller in Auto Position Conversion Mode.
4. Waiting for Interrupt Mode
Touch Screen Controller generates interrupt (INT_TC) signal when the Stylus is down. Waiting for Interrupt
Mode setting value is rADCTSC=0xd3; // XP_PU, XP_Dis, XM_Dis, YP_Dis, YM_En.
After Touch Screen Controller generates interrupt signal (INT_TC), Waiting for interrupt Mode must be cleared.
(XY_PST sets to the No operation Mode)
Standby Mode
Standby mode is activated when ADCCON [2] is set to '1'. In this mode, A/D conversion operation is halted and
ADCDAT0, ADCDAT1 register contains the previous converted data.