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19-2480; Rev 0; 6/02
MXB7846 Evaluation Kit/Evaluation System
General Description
The MXB7846 evaluation system (EV system) is a complete touch-screen controller data-acquisition system consisting of a MXB7846 evaluation kit (EV kit) and a Maxim 68HC16MODULE-DIP microcontroller (C) module. The MXB7846 is an industry-standard, 4-wire touch-screen controller. Windows(R) 98/2000 software provides a handy user interface to exercise the features of the MXB7846. Order the complete EV system (MXB7846EVC16) for comprehensive evaluation of the MXB7846 using a personal computer. Order the EV kit (MXB7846EVKIT) if the 68HC16MODULE module has already been purchased with a previous Maxim EV system, or for custom use in other C-based systems. To evaluate the MXB7843, request a free sample of the MXB7843EEE.
Windows is a registered trademark of Microsoft Corp.
Features
o Proven PC Board Layout o Complete Evaluation System o Convenient Test Points Provided On Board o Data-Logging Software o Fully Assembled and Tested
Evaluates: MXB7843/MXB7846
Ordering Information
PART MXB7846EVKIT MXB7846EVC16 TEMP RANGE 0C to +70C 0C to +70C INTERFACE TYPE User supplied Windows software
Component List
DESIGNATION C1 C2, C3, C4, C12 QTY 1 4 DESCRIPTION 0.01F ceramic capacitor 0.1F ceramic capacitors 10F 20%, 10V (6.3V min) X7R ceramic capacitor Taiyo Yuden LMK325BJ106MN Open 4.7F 20%, 10V X7R ceramic capacitor Taiyo Yuden LMK316BJ475ML 3-pin header 2-pin header R1 R2-R7 TP1, TP2 U1 U2 U3, U4 C13 1 U5 None None JU1 JU2 1 1 None None 1 0 2 1 1 2 1 1 1 1 1 DESIGNATION J1 QTY 1 DESCRIPTION 2 x 20 right-angle socket, SamTec SSW-120-02-S-D-RA 100k 5% resistor Open 8-pin headers MXB7846EEE MAX6192ACSA MAX1840EUB MAX1615EUK-T 3 1/2in software disk MXB7846 data sheet MXB7846 EV kit data sheet 68HC16MODULE manual
C5
1
C6-C11
0
________________________________________________________________ Maxim Integrated Products
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For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
MXB7846 Evaluation Kit/Evaluation System Evaluates: MXB7843/MXB7846
MXB7846 Stand-Alone EV Kit
The MXB7846 EV kit provides a proven PC board layout to facilitate evaluation of the MXB7846. It must be interfaced to appropriate timing signals for proper operation. Connect +3V to VDD, and connect ground return to GND (Figure 7). Refer to the MXB7846 data sheet for timing requirements. If used with a +5V system, the on-board MAX1615 linear regulator and MAX1840 level translators can be used. Note that the MAX1840 level translators cannot withstand a supply voltage exceeding +5.5V. 4) Connect a cable from the computer's serial port to the C module. If using a 9-pin serial port, use a straight-through, 9-pin female-to-male cable. If the only available serial port uses a 25-pin connector, a standard 25-pin to 9-pin adapter is required. The EV kit software checks the modem status lines (CTS, DSR, DCD) to confirm that the correct port has been selected. 5) Connect your touch-screen panel to the X+, X-, Y+, and Y- terminals of the EV kit. 6) Install the EV system software on your computer by running the INSTALL.EXE program on the floppy disk. The program files are copied and icons are created for them in the Windows Start Menu. 7) Turn on the power supply. 8) Start the program by opening its icon in the Start Menu. 9) The program prompts you to connect the C module and turn its power on. Slide SW1 to the ON position. Select the correct serial port, and click OK. The program automatically loads code into the module. 10) Once the module is loaded, the main window appears (see Figure 1). Verify the connections by making a large circle on the touch-screen surface. 11) After verifying that the X and Y axes are wired correctly, bring up the Calibration tab, click Measure Touchscreen Idle Threshold, and then click Erase. The right side of the main window should now track the touch screen.
MXB7846 EV System
The MXB7846EVC16 EV system operates from a usersupplied +7VDC to +20VDC power supply. Windows 98/2000 software running on an IBM PC interfaces to the EV system board through the computer's serial communications port. See the Quick Start section for setup and operating instructions.
Quick Start
Recommended Equipment
Before you begin, the following equipment is needed: * Maxim MXB7846EVKIT and 68HC16MODULE interface board * * * * * A small DC power supply, such as a +12VDC 0.25A plug-in transformer, or a 9V battery A computer running Windows 98/2000 A spare serial communications port, preferably a 9-pin plug A serial cable to connect the computer's serial port to the 68HC16MODULE Resistive 4-wire touch-screen panel
Detailed Description of Software
The evaluation software tracks the touch screen in the right half of the main window. The Measurement tab tracks touch-screen input, device temperature, and auxiliary inputs. The Calibration tab provides simple, linear adjustment of the software's voltage and temperature displays. The Control tab determines the control word used for each input channel. The Low Level tab controls the 68HC16 module's QSPI interface parameters. The Output Codes tab displays the raw, unprocessed output code value of each input channel, in binary, unsigned decimal, and as a percent of full scale.
Procedure
Words in boldface indicate user-selectable features in the software. 1) Ensure that the jumper settings are in the default position (see Table 1). 2) Carefully connect the boards by aligning the 40-pin header of the MXB7846 EV kit with the 40-pin connector of the 68HC16MODULE-DIP module. Gently press them together. The two boards should be flush against one another. 3) With the power off, connect a +7VDC to +20VDC power supply to the C module at the terminal block located next to the on/off switch, along the top edge of the C module. Observe the polarity marked on the board.
Reference Voltage
The evaluation software assumes a +2.5V reference voltage, unless otherwise specified. To override this value, select the Calibration tab, and type the new reference voltage into the field named Reference Voltage.
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MXB7846 Evaluation Kit/Evaluation System Evaluates: MXB7843/MXB7846
NOTE: THE EVALUATION SOFTWARE TRACKS THE TOUCH SCREEN IN THE RIGHT HALF OF THE MAIN WINDOW. THE MEASUREMENT TAB TRACKS TOUCH-SCREEN INPUT, DEVICE TEMPERATURE, AND AUXILIARY INPUTS.
Figure 1. MXB7846 Touch-Screen Controller EV Kit--Measurement Tab
Increasing Acquisition Time
A high-impedance source can require a longer acquisition time for accurate measurement. From the evaluation software's Low Level tab, set QSPI clock to a sufficiently slow serial clock speed. The minimum clock rate the 68HC16 module supports is 33kHz, which corresponds to an acquisition time of 91s.
68HC16MODULE, the MAX1615 (U5) provides +3V power to the MXB7846, and the MAX1840 level shifters (U3 and U4) translate the 68HC16MODULE's +5V logic signals to +3V logic. See Figure 7, MXB7846 EV Kit Schematic, and refer to the MXB7846 data sheet.
Touch-Screen Equivalent Circuit
For prototyping purposes, a 4-wire resistive touch screen can be simulated using two variable resistors connected by a resistor and a switch. Variable resistor X, connected between X+ and X-, should be approximately 100 to 500. Variable resistor Y, connected between Y+ and Y-, should be approximately 100 to 500. Connect the center wipers of the two variable resistors using a fixed resistor of approximately 300, simulating the touch resistance (Figure 6).
Detailed Description of Hardware
The MXB7846 (U1) is an industry-standard, 4-wire touch-screen controller. Resistors R2-R7 and capacitors C6-C11 are reserved for optional user-supplied, single-pole, low-pass, anti-aliasing filters. C3 bypasses the ADC's voltage reference. When plugged into the
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MXB7846 Evaluation Kit/Evaluation System Evaluates: MXB7843/MXB7846
NOTE: THE CALIBRATION TAB PROVIDES SIMPLE, LINEAR ADJUSTMENT OF THE SOFTWARE'S VOLTAGE AND TEMPERATURE DISPLAYS.
Figure 2. MXB7846 Touch-Screen Controller EV Kit--Calibration Tab
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MXB7846 Evaluation Kit/Evaluation System Evaluates: MXB7843/MXB7846
NOTE: THE CONTROL TAB DETERMINES THE CONTROL WORD USED FOR EACH INPUT CHANNEL.
Figure 3. MXB7846 Touch-Screen Controller EV Kit--Control Tab
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MXB7846 Evaluation Kit/Evaluation System Evaluates: MXB7843/MXB7846
NOTE: THE LOW LEVEL TAB CONTROLS THE 68HC16 MODULE'S QSPI INTERFACE PARAMETERS.
Figure 4. MXB7846 Touch-Screen Controller EV Kit--Low-Level Tab
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MXB7846 Evaluation Kit/Evaluation System Evaluates: MXB7843/MXB7846
NOTE: THE OUTPUT CODES TAB DISPLAYS THE RAW, UNPROCESSED OUTPUT CODE VALUE OF EACH INPUT CHANNEL, IN BINARY, UNSIGNED DECIMAL, AND AS A PERCENT OF FULL SCALE.
Figure 5. MXB7846 Touch-Screen Controller EV Kit--Output Codes
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MXB7846 Evaluation Kit/Evaluation System Evaluates: MXB7843/MXB7846
Table 1. Jumper Functions
JUMPER JU1 JU1 JU1 JU2 JU2 POSITION 1-2 Open 2-3* Closed* Open FUNCTION REF = VDD REF = internal reference (MXB7846 only) REF = U2, MAX6192 IRQ connects to C GPIO pin IRQ not connected to C
XY100 TO 500 X+ 300 100 TO 500 Y+
*Default configuration
Evaluating the MXB7843
The MXB7843 behaves like the MXB7846 with no temperature measurement, no internal reference, and an additional AUX input instead of BAT.
Figure 6. Touch-Screen Equivalent Circuit
Troubleshooting
Problem: No output measurement. System seems to report zero voltage, or fails to make a measurement. Check +5V and +3V supply voltages. Check the +2.5V reference voltage using a digital voltmeter. Use an oscilloscope to verify that the CS signal is being strobed. Problem: Measurements are erratic, unstable; poor accuracy. Check the reference voltage using a digital voltmeter. Use an oscilloscope to check for noise. When probing for noise, keep the oscilloscope ground return lead as short as possible, preferably less than 1/2in (10mm). Problem: Trapezoidal distortion on touch screen. Insufficient acquisition time can cause position-sensitive errors in touch-screen position measurement. Increase the acquisition time by reducing the clock rate. On the software's Low-Level tab, select a slower QSPI Clock setting.
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MXB7846 Evaluation Kit/Evaluation System Evaluates: MXB7843/MXB7846
VCC 1 C1 0.01F 2 C6 OPEN 3 C7 OPEN 4 C8 OPEN 5 C9 OPEN 6 7 8 R6 SHORT C10 OPEN 8 C11 OPEN AUX REF 9 C3 0.1F GND PENIRQ 11 VCC 7 BAT VDD 10 C2 0.1F C5 10F 10V YDOUT 12 7 VCC 8 1 2 3 JU1 6 OUT 2 IN C4 0.1F XBUSY 13 5 6 JU2 MISO R1 100k VCC VCC Y+ X+ CS 15 2 14 3 4 VDD DCLK 16 TP2 1 SCLK CS
R2 SHORT TP1 1 2 3 4 5 6 R5 SHORT R4 SHORT R3 SHORT
U1
MXB7846
DIN MOS1 BUSY
U2
MAX6192
GND 4
R7 SHORT
Figure 7. MXB7846 EV Kit Schematic (Sheet 1 of 2)
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MXB7846 Evaluation Kit/Evaluation System Evaluates: MXB7843/MXB7846
J1-5 J1-6 J1-9 J1-10 J1-11 J1-12 J1-13 J1-14 J1-15 J1-16 J1-17 J1-18 J1-19 J1-20 J1-21 J1-22 J1-23 J1-24 J1-25 J1-26 J1-28 J1-29 J1-30 J1-32 J1-33 J1-34 J1-39
HEADER-40P N.C. J1-31 N.C. N.C. N.C. N.C. N.C. N.C. N.C. N.C. N.C. N.C. N.C. N.C. N.C. N.C. N.C. N.C. N.C. N.C. N.C. N.C. N.C. N.C. N.C. J1-27 N.C. N.C. N.C. J1-40 N.C. N.C. J1-38 +5V 5 SHDN GND 6 C13 4.7F 10V 4 RIN RST 7 CS VCC CLK 8 SCLK J1-37 3 CIN C12 0.1F J1-8 J1-7 +5V +5V 2 J1-35 1 DATA I/O 10 MISO J1-1 J1-2 J1-3 J1-4 J1-36 +5V
1
DATA
I/O
10
BUSY
U4
2
MAX1840
DVCC VCC 9
VCC
3
CIN 8
CLK 4 RIN RST VCC +5V
MOS1
U3
7
MAX1840
DVCC VCC 9
5
SHDN
GND
6
1
+5V IN
U5
2 GND
SHDN
5
MAX1615
5/3 (FB) 4
3
OUT
Figure 7. MXB7846 EV Kit Schematic (Sheet 2 of 2)
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MXB7846 Evaluation Kit/Evaluation System Evaluates: MXB7843/MXB7846
1.0"
1.0"
Figure 8. MXB7846 EV Kit Component Placement Guide-- Component Side
Figure 9. MXB7846 EV Kit PC Board Layout--Component Side
1.0"
Figure 10. MXB7846 EV Kit PC Board Layout--Solder Side
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 11 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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