MAX1233/MAX1234觸摸屏控制器入門
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ADC_control_RES11 /* 12-bit resolution */
ADC_control_AVG00 /* no averaging */
ADC_control_CNR00 /* conversion rate 3.5μs */
ADC_control_RFV /* RFV=1: VREF=2.5V */
0x0040 0x3301
T R T1
0x8009 0x0000
T R T2
0x800a 0x0000
2.8) 將TEMP1轉(zhuǎn)換結(jié)果譯為物理值
下面的C/C++偽代碼片斷總結(jié)了DEMO1234程序是怎樣解釋TEMP1轉(zhuǎn)換結(jié)果的。/* ADC control resolution value selects num_codes 4096 (12-bit), 1024 (10-bit), or 256 (8-bit) */int num_codes = 4096; /* ADC_control_RES11: 12-bit resolution *//* Voltage that corresponds to the full-scale ADC code; may be internal 1V or 2.5V ref, or ext ref. */double ADC_fullscale_voltage = 2.5; /* ADC_control_RFV=1: VREF=2.5V. RFV=0: VREF=1.0V. *//* TEMP1_code is the 16-bit result read by SPI command 0x8009 */double TEMP1_Voltage = (TEMP1_code * ADC_fullscale_voltage) / num_codes;/* Calibration values */const double Temp1V_Room = 0.590; // temp1 voltage at room temperature 25Cconst double Temp1K_Room = 298.15; // Room temperature Kelvins (298.15K=25C)const double Temp1V_Per_K = -0.002; // TempCo -2mV per degree C/* Convert to absolute temperature */double Kelvin = (TEMP1_Voltage - Temp1V_Room) / Temp1V_Per_K + Temp1K_Room;/* Optional conversion to commonly used temperature units */double Centigrade = Kelvin - 273.15;double Fahrenheit = (Centigrade * 9.0 / 5.0) + 32;
2.9) 將TEMP1和TEMP2轉(zhuǎn)換結(jié)果譯為物理值
下面的C/C++偽代碼片斷總結(jié)了DEMO1234程序是怎樣解釋TEMP1和TEMP2轉(zhuǎn)換結(jié)果的。TEMP2只在和TEMP1對(duì)比時(shí)才有意義。/* ADC control resolution value selects num_codes 4096 (12-bit), 1024 (10-bit), or 256 (8-bit) */int num_codes = 4096; /* ADC_control_RES11: 12-bit resolution *//* Voltage that corresponds to the full-scale ADC code; may be internal 1V or 2.5V ref, or ext ref. */double ADC_fullscale_voltage = 2.5; /* ADC_control_RFV=1: VREF=2.5V. RFV=0: VREF=1.0V. *//* TEMP1_code is the 16-bit result read by SPI command 0x8009 */double TEMP1_Voltage = (TEMP1_code * ADC_fullscale_voltage) / num_codes;/* TEMP2_code is the 16-bit result read by SPI command 0x800a */double TEMP2_Voltage = (TEMP2_code * ADC_fullscale_voltage) / num_codes;/* Calibration values */const double K_Per_Temp21_Delta_V = 2680.0; // nominal 2680 5/27/2002/* Convert to absolute temperature */double Kelvin = (TEMP2_Voltage - TEMP1_Voltage) * K_Per_Temp21_Delta_V;/* Optional conversion to commonly used temperature units */double Centigrade = Kelvin - 273.15;double Fahrenheit = (Centigrade * 9.0 / 5.0) + 32;
2.10) 測量外部電壓輸入AUX1、AUX2、BAT1、BAT2和溫度
表9. ADC測量命令序列DEMO1234 Command | Action (Triggered by A/D3210 Bits) | SPI data in |
T MB | Measure BAT1/4, BAT2/4, AUX1, AUX2, TEMP1, TEMP2 with 12-bit resolution and 3.5μs conversion rate | 0x0040 0x2f01 0x8005 0x0000 0x8006 0x0000 0x8007 0x0000 0x8008 0x0000 0x8009 0x0000 0x800a 0x0000 |
T W AC 2f01 | Trigger ADC scan of BAT1-2, AUX1-2, TEMP1-2; ADC control word 0x2f01 means: ADC_control_wr_demand_scan ADC_control_ AD1011 /* measure AUX1 etc. */ ADC_control_RES11 /* 12-bit resolution */ ADC_control_AVG00 /* no averaging */ ADC_control_CNR00 /* conversion rate 3.5μs */ ADC_control_RFV /* RFV=1: VREF=2.5V */ | 0x0040 0x2f01 |
T R B1 | Read BAT1 result BAT1 _code | 0x8005 0x0000 |
T R B2 | Read BAT2 result BAT2_code | 0x8006 0x0000 |
T R A1 | Read AUX1 result AUX1 _code | 0x8007 0x0000 |
T R A2 | Read AUX2 result AUX2 _code | 0x8008 0x0000 |
T R T1 | Read TEMP1 result TEMP1 _code | 0x8009 0x0000 |
T R T2 | Read TEMP2 result TEMP2 _code | 0x800a 0x0000 |
3) 觸摸屏實(shí)例
下面的例子解釋了怎樣使用DEMO1234.EXE程序來獲得觸摸屏數(shù)據(jù)。3.1) 低成本商用觸摸屏
在互聯(lián)網(wǎng)上搜索"PDA Digitizer/Glasstop"，尋找合適的替代觸摸屏。高清觸摸屏玻璃的價(jià)格范圍在50美元至10美元之間，價(jià)格取決于型號(hào)以及玻璃是否全部貼在顯示屏上。3.2) 連接觸摸屏和評(píng)估板
MAX1234評(píng)估板提供突出插頭H5/H6來連接10mm柔性電纜或者長度更短的電纜。H6連接器的間距是0.5mm，比實(shí)際觸摸屏柔性電纜間距更精細(xì)。把柔性電纜插入H6，上鎖，選擇位于四條柔性電纜中每一電纜中心位置的H5引腳。跳接器連接H5和標(biāo)有U1的X+、Y+、X-以及Y-測試點(diǎn)。3.3) 檢驗(yàn)觸摸屏的連接
第一次連接觸摸屏?xí)r，通過下面的步驟來驗(yàn)證X和Y連接是否正確?？梢杂袔讉€(gè)觸摸屏交叉連接，但大部分不會(huì)正常工作。在這些例子中，我們假設(shè)X- = left，X+ = right，Y- = top，Y+ = bottom。表10. 觸摸屏物理連接驗(yàn)證命令序列
DEMO1234 Command | Action | SPI data in | Verification |
| Connect DVM to X+/GND | |||
T MD | No measurement; drive Y+,Y- | 0x0040 0x3701 | |
| Touch top left | X+ = approx. Y- | ||
| Touch top right | X+ = approx. Y- | ||
| Touch bottom left | X+ = approx. Y+ | ||
| Touch bottom right | X+ = approx. Y+ | ||
| Connect DVM to Y+/GND | |||
T ME | No measurement; drive X+,X- | 0x0040 0x3b01 | |
| Touch top left | Y+ = approx. X- | ||
| Touch top right | Y+ = approx. X+ | ||
| Touch bottom left | Y+ = approx. X- | ||
| Touch bottom right | Y+ = approx. X+ |
表11. 糾正觸摸屏連接問題
| Symptom | Correction |
| Touch coordinates are mirrored top-to-bottom | Swap the Y+ and Y- connections |
| Touch coordinates are mirrored left-to-right | Swap the X+ and X- connections |
| Touch coordinates are rotated 180 degrees | Swap the X+ and X- connections, and swap the Y+ and Y- connections |
| Touch coordinates are mirrored diagonally | Swap the X+ and Y+ connections, and swap the X- and Y- connections |
| Touch coordinates do not seem to track, and the distortion is not a simple flip/rotate/mirror transformation | Swap the X+ and Y+ connections; if distortion persists, swap the X+ and Y- connections; if distortion still persists, disconnect touch screen and use DVM to verify X+ to X- resistance and Y+ to Y- resistance; verify with no touch X+ and X- are isolated from Y+ and Y- |
3.4) 檢測觸摸屏的操作：根據(jù)需要掃描
在配置MAX1234檢測觸摸屏操作，根據(jù)需要數(shù)字化接觸屏的位置時(shí)，寫入寄存器0x40 (ADC控制)，其PENSTS=0，ADSTS=0 (請(qǐng)參考MAX1233/MAX1234數(shù)據(jù)資料的表6)。讀取寄存器0x00 (X軸)后，檢測到后續(xù)的觸摸屏操作時(shí)，/PENIRQ信號(hào)鎖存至低電平，在寫入ADC控制寄存器測量X、Y軸之前，保持低電平。表12. 觸摸屏檢測命令序列：根據(jù)需要掃描
DEMO1234 Command | Action | SPI data in | Verification |
T W AC 0b01 | Demand scan | 0x0040 0x0b01 | |
T R AX | Read conversion result register X | 0x8000 0x0000 | |
P R
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