Renesas H8SX Data Enable, RGB Red Green Blue Data, Touch Screen Circuit, Y Drive Xdrive

Direct Drive LCD Design Guide

entire panel to fill with valid pixels is the maximum refresh rate. Displays in existing media systems usually have refresh rates between 48Hz and 120Hz to avoid visible flicker.

HSync, VSync and Dot Clock are all generated using TPU channels of the H8S or H8SX microcontrollers. The TPU allows timer compare actions which synchronize these signals to the ExDMA request line. This ensures that the clocks are generated when valid data is available on the bus.

3.1.5Data Enable

Many panels require an additional signal to frame the valid data – this enable signal is sent at the time the valid data is latched onto the bus – the panel will then clock in the data on the next edge of Dot Clock. It provides added synchronization for the timing of data, but this signal can often be left in the active state if the Dot Clock synchronization to the data is predictable.

3.1.6RGB (Red Green Blue) Data

The data is presented to the panel in parallel. LCD panels have connections for 6 or 8bits of data for each color totaling 18 or 24bits of color resolution. Our solution uses a 16bit data bus, so the most significant bits of the data are presented to the panel. RGB 5-6-5 is the most common 16 bit solution. The least significant bits can be tied low, or better still, to the MSB which would give a slightly improved range over tying to ground.

Specifically with respect to Renesas H8S and H8SX devices, we use the ExDMA module to control the data bus transfers.

3.1.7Touch Screen

Our support is currently for popular resistive touch screen panels which have 4 connections (endpoints of an X axis resistance and Y axis resistance). These inputs provide resistances proportional to the touched location particular X and Y coordinates on the panel.

The host system (microcontroller plus logic) drives the resistive endpoints with a known reference voltage, and the level on the channel is read into an analog to digital converter (ADC). With calibration and scaling in the microcontroller driver code, it is possible to pinpoint the area of the panel that was touched. Action can be taken accordingly.

An example of interface circuitry between the MCU and touch-screen is shown in Figure 6 below.

Y_DRIVE

X_DRIVE

VCC

1

U1A

23

HC126A

4

U1B

56

HC126A

10

U1C

98

HC126A

13

U1D

1211

HC126A

J4

4

3

2

1

MOLEX_52044

R2

1K C1 10nF

R4

1K C2 10nF

R9

1K C4 10nF

R11

1K C5 10nF

TOUCH_YU

R1

DNF

TOUCH_XL

R3

DNF

TOUCH_YL

R8

DNF

TOUCH_XR

R10

DNF

Figure 8 Touch Screen Circuit

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