emWin - SEGGER Microcontroller

32 CHAPTER Introduction to emWin
1.6 Screen and coordinates
The screen consists of many dots that can
be controlled individually. These dots are
called pixels. Most of the text and drawing
functions that emWin offers in its API to the
user program can write or draw on any
specified pixel.
The horizontal scale is called the X-axis,
whereas the vertical scale is called the Yaxis.
Coordinates are denoted as a pair
consisting of an X- and a Y-value (X, Y).
The X-coordinate is always first in routines
that require X and Y coordinates. The upper
left corner of the display (or a window) has
per default the coordinates (0,0). Positive
X-values are always to the right; positive Y-values are always down. The above graph
illustrates the coordinate system and directions of the X- and Y- axes. All coordinates
passed to an API function are always specified in pixels.
1.7 How to connect the display to the micro controller
emWin handles all access to the display. Virtually any display controller can be supported,
independently of how it is accessed. For details, refer to the chapter “Configuration”
on page 1025. Also, get in contact with us if your display controller is not
supported. We are currently writing drivers for all display controllers available on the
market and may already have a proven driver for the display controller that you
intend to use. It is usually very simple to write the routines (or macros) used to
access the display in your application SEGGER Microcontroller GmbH & Co. KG offers
the service of making these customizations for you, if necessary with your target
hardware.
It does not really matter how the display is connected to the system as long as it is
somehow accessible by software, which may be accomplished in a variety of ways.
Most of these interfaces are supported by a driver which is supplied in source code
form. This driver does not normally require modifications, but is configured for your
hardware by making changes in the file LCDConf.h. Details about how to customize a
driver to your hardware as necessary are provided in the chapter “Display drivers” on
page 907. The most common ways to access the display are described as follows. If
you simply want to understand how to use emWin, you may skip this section.
Display with memory-mapped display controller:
The display controller is connected directly to the data bus of the system, which
means the controller can be accessed just like a RAM. This is a very efficient way of
accessing the display controller and is most recommended. The display addresses are
defined to the segment LCDSEG, and in order to be able to access the display the
linker/locator simply needs to be told where to locate this segment. The location
must be identical to the access address in physical address space. Drivers are available
for this type of interface and for different display controllers.
Display with display controller connected to port / buffer
For slower display controllers used on fast processors, the use of port-lines may be
the only solution. This method of accessing the display has the disadvantage of being
somewhat slower than direct bus-interface but, particularly with a cache that minimizes
the accesses to the display, the display update is not slowed down significantly.
All that needs to be done is to define routines or macros which set or read the hardware
ports/buffers that the display is connected to. This type of interface is also supported
by different drivers for the different display controllers.
UM03001 User & Reference Guide for emWin V5.18 © 1997 - 2012 SEGGER Microcontroller GmbH & Co. KG