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參數(shù)資料
| 型號(hào)： | LU7790H2D1A |
| 廠商： | Sharp Corporation |
| 英文描述： | Interface Add-on Board(接口擴(kuò)充卡) |
| 中文描述： | 接口附加委員會(huì)（接口擴(kuò)充卡） |
| 文件頁數(shù)： | 5/10頁 |
| 文件大?。?/td> | 172K |
| 代理商： | LU7790H2D1A |
Interface Add-on Board
LU7790H2D1A
Data Sheet
Page 5
The ADC provides a bidirectional 8-bit parallel, bus-
compatible interface that is connected to the data bus D0
to D7 of the LH77790A/B. This allows Read/Write access
to the ADC through simple byte transfer operations.
The CS\ of the ADC is connected to CE5 of the
LH77790A/B. CE5 must be programmed for 8-bit data
width and one wait state, and associated with a non-
cached memory segment with Read and Write access
privileges. Since no address signals are connected to
the ADC, any address within the relevant memory seg-
ment can be used to read or write the ADC.
Channel 0 of the ADC is used for the digitization of
the voice input signal. Channels 1 and 2 are used for
the touch screen interface.
For detailed information on the operation of the
ADC, please consult the proper data sheet from
National Semiconductor.
Touch Screen Interface
The add-on board provides a 4-wire interface to
resistive touch screens, for example, from Dynapro.
In principle, a resistive touch screen works as a two
dimensional voltage divider where the dividing ratios in
the X- and the Y-axes are determined by the point
where the screen is being touched. To determine the X-
and Y-coordinate of the touch point, a voltage is applied
alternately across the X- and the Y- axis of the screen
and the voltage at the touch point is measured.
Channel 1 of the ADC is used to measure the X-
coordinate, channel 2 is used to measure the Y-coordi-
nate of the touch point.
The transistor pairs Q1/Q2 and Q3/Q4 are used to
switch the voltage across the touch screen. The tran-
sistors are controlled by the PIO pins PB0 to PB3 of the
LH77790A/B. These port pins must be set to output
mode in the LH77790A/B.
Table 1 describes the setting of the PIO pins PB0 to
PB3 for measuring the coordinates of a touch point.
NOTE:
Other combinations of PB0 to PB3 settings could result in
excessive current flowing through the touch screen which could dam-
age the touch screen as well as the driver circuitry on the
LU7790H2D1A board.
The 4-pin header JP1 provides the 4-wire interface
signals for a resistive touch screen.
The pin assignment of JP1 was chosen to allow a
direct pin-to-pin connection to a Dynapro 5.7" touch
screen with pinout ‘T’, Dynapro part number 95644.
Other touch screens can be connected as long as the
proper pin assignment is observed. Since different
touch screens have different pin assignments, only a
general rule can be given here for the connection of a
touch screen.
Figure 7 shows a fictional touch screen and its
proper connection to J1.
Touch screen resistance is relatively low. To
achieve high precision operation of the touch screen,
keep the wires between the add-on board and the
touchscreen as short as possible.
For more information and software examples on the
use of the touch screen interface, please see the
respective Application Notes for the LH77790A/B.
Table 1. Touch Screen Control Settings
FUNCTION
PB0
PB1
PB2
PB3
ADC
CHANNEL
NUMBER
Measure
X-coordinate
Measure
Y-coordinate
Disable Touch
Screen
HIGH
LOW
LOW
HIGH
1
LOW
HIGH HIGH
LOW
2
HIGH
LOW
HIGH
LOW
—
Figure 6. JP1 Pin Assignment
Figure 7. Touch Screen Connection
1
JP 1
4
JP1 PIN
NUMBER
1
2
3
4
LEFT
BOTTOM
RIGHT
TOP
TOUCH SCREEN
ASSIGNMENT
7790H2-6
TOP
TOUCH SCREEN
BOTTOM
4
JP1 PIN NUMBERS
1 2 3
LEFT
RIGHT
7790H2-7
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