SIM225 Technical Reference Manual
24
© Serious Integrated, Inc.
SIM225_TRM_A1ENUS
Revision A1
can deliver pixel data directly from external RAM to the LCD display. This technology is called “Direct
Drive” and can deliver excellent user interface experiences at low hardware cost.
For a detailed explanation of Direct Drive operation, consult the Renesas
RX600 Series Direct Drive LCD
Demonstration Application Note
. The concept is straightforward: the RX MCU instructs the SDRAM to
deliver the pixel data to the LCD panel at exactly the right frequency (the “dot clock”) so that each line of
the screen is “painted” in the correct sequence and at the right time. Typically this painting of the frame is
done every 60Hz (16ms) and the paint time is only about 8ms for the frame. Therefore there is a “blank”
time that represents about 30-50% of the total 16ms frame time. During the painting time, the MCU
software
must not access the SDRAM, as the MCU access can disrupt the timing of the data delivery to the
LCD from the SDRAM and cause visible flickering and shearing on the LCD screen. However, the MCU is
free to manipulate and access the SDRAM during the blanking time. Both Renesas and
Serious software
include special “monitor” tasks to lock/unlock tasks needing access to the external RAM without
disrupting the LCD operation. Software that uses the external SDRAM needs to be written with the
understanding that it is subject to frequent ~8ms delays while the frame is being painted.
The overall advantage of a Direct Drive system is lower cost and circuit complexity. With almost no
external components, no graphics controller, no dedicated frame buffers, no dual ported RAM or arbiters,
one can create a complete graphic LCD output very inexpensively with excellent visual results.
The LCD panel has two timing modes: VSYNC/HSYNC mode and DEN mode. The SIM225 uses DEN mode
which provides better Direct Drive performance and uses less pins and software overhead than
VSYNC/HSYNC mode. In DEN mode, the LCD’s
VSYNC#
and
HSYNC#
pins are both always pulled inactive,
and the
DEN
signal (when active) indicates when data is being clocked into the LCD panel.
DEN
is inactive
a minimum of 45 clocks between lines, allowing the 480 pixel line previously clocked into the chip to be
driven to the screen.
DEN
is inactive a minimum of 13 lines to signal that the next line is the beginning of
a new 272 line frame.
The no-cost SHIPWare software at
mySerious.com
includes all initialization code, drivers, and
utilities to enable Direct Drive operation, including portrait and landscape modes and adjustable
frame rates. This software is available after account sign-up and registration of your SIM225
serial number.
The
Serious Human Interface™ Platform
software system has fully-integrated and optimized
Direct Drive drivers and frame buffer management, making the Direct Drive system transparent
to the GUI designer.
TOUCH
Some SIM225 family members include a resistive touch layer bonded to the LCD display. The layer can
return an analog voltage in two dimensions to be read by the MCU’s analog-to-digital converters and
translated with a software algorithm into a pixel hit position. These four input signals are as follows:
Signal
Description
MCU Port
TOUCH_YB
Y-/YB/YDown
AN000/P40/IRQ8-DS
TOUCH_XR
X+/XR/XRight
AN001/P41/IRQ9-DS
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