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LOOKING GOOD

Using a Graphics-Based LCD
Module with C
by Bob Perrin and Tak Auyeung

Start ý Software Overview ý The Bottom Layer ý Initializing the LCD Display ý Shadow Display ý Drawing Dots and Lines ý Printing Text ý Extensions ý Sources and PDF

SOFTWARE OVERVIEW

The software referenced in this article can be downloaded, the zip contains two files glcd.c and glcd.h. You can also download them from www.mobots.com.

The C code in glcd.c implements the API level functions as shown in Table 1. These functions constituted a minimally functional API for a graphics-based display. Because the code is written completely in ANSI C, it should be portable to your target system and easily modified to suit your application.

The HDG12864F-1 COG module uses an Epson SED1565 LCD controller. If you want to modify the drivers, get Epsonýs SED1565 Technical Manual. [3] There is also a datasheet for the SED1565, but the Technical Manual is much more useful.

If you want to do additional software modifications specifically for the JK Microsystems V25+ Flashlite, get the V25+ and V35+ Users Manual from NEC. [4] Unfortunately, this publication is only available in print (not PDF), so you need to request it from NEC directly. You may be able to do this over the Internet, but we had better luck with the literature request phone line at (800) 366-9782.

OBJECTIVES AND SPECIFICATIONS

The main objective of the software driver of the graphics LCD is to provide an application programming interface (API) to isolate the application software from the details of the LCD hardware. With the proper API, any change to the graphics LCD hardware should not significantly affect the application program.

With a graphics LCD, an application can display both graphics and text. Therefore, it is important to supply methods to display text and graphics. For emphasis (or to save screen space), it is helpful to be able to use fonts of multiple sizes and shapes. The basic graphics primitives include dot plotting, line drawing, as well as filled rectangles.

Other useful methods include the ability to display bitmaps from a file and capture bitmaps to a file. However, these methods are not necessary to illustrate how to use a graphics LCD.

The driver software referred to in this article is developed using Borland C++ 4.52 and mostly ANSI-C compliant constructs with no "C++ only" constructs. The FAR keyword is not ANSI compliant, but is required by the Borland compiler to access the special function registers in the V25+. [1] The intentional avoidance of C++ constructs allows more developers to use the sample code.

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