Texas Instruments Stellaris RDK-IDM-SBC, User Manual

Stellaris® IDM Single-Board Computer

November 28, 2011

17

Control Interface

The Color LCD module has a built-in controller IC with a multi-mode parallel interface. The EVB 
uses an 8-bit 8080 type interface with GPIO Port D providing the data bus.

Backlight

The white LED backlight must be powered for the display to be clearly visible.   U9 (FAN5331B) 
implements a 20mA constant-current LED power source to the backlight. The backlight is 
controlled by the microcontroller using GPIO PJ7. The timer connected to this pin could be 
configured to provide a modulated dimming signal

Because the FAN5331B operates in a constant current mode, its output voltage will jump up if the 
LCD should become disconnected. To prevent over-voltage failure of the IC or diode D5, a zener 
(D6) clamps the voltage. The current will limit to 20mA, but the total board current will be higher 
than when the LCD panel is connected. If the LCD is not connected, avoid over-heating the 
backlighting circuit, by setting PJ7 low to completely shut-down the circuit.

Power

The LCD module has internal bias voltage generators and requires only a single 3.3V dc supply.

Resistive Touch Panel

The 4-wire resistive touch panel interfaces directly to the microcontroller, using 2 ADC/GPIO 
channels and 2 GPIO-only signals. The microcontroller creates a resistive divider by driving Y+ 
and Y- with 3.3V (V

OH

) and 0V (V

OL

) respectively. A voltage representing the Y-axis position is 

then read on the X+ terminal. The process then repeats for the other axis. Note that when the 
screen is not being touched, the X+ or Y+ sense inputs are floating. The software implements a 
special state to discharge the capacitor (C10 or C15) to 0V and detect this condition. 

Refer to the StellarisWare® source code for additional information on touch panel implementation.

Table 2-1. LCD-Related Signals

Microcontroller Pin

Board Function

PE6/ADC1

Touch X+

PE3

Touch Y-

PE2

Touch X-

PE7/ADC0

Touch Y+

PB7 LCD 

Reset

PD0..7

LCD Data Bus 0..7

PH7

LCD Data/Control Select

PB0 LCD 

Read 

Strobe

a

a.

LCD Read function not available on LM3S9B92 Rev B1. See rework note in 
schematic.

PH6

LCD Write Strobe

PJ7

Backlight control