Graphics for dummies

rovtech · Joined: 24 Sep 2006 Posts: 262

How does one get started in driving a 128x64 dot graphics display.
This is a ST7920.
Is there a graphics library for CCS C?
How do you mix graphics and alphanumerics?
Do I have to write this from scratch?

temtronic · Posted: Wed Mar 28, 2012 5:34 am

1) read the datasheet.Knowledge is power!

2) constuct a breadboard with both PIC,GLCD AND ALL support devices.

3) cut code to confirm it works in simple text mode.

4) read datasheet again, google GLCD device for more info.

If you can't locate someone else's code you have 2 options

a) cut the code yourself.It is a simple device,should take maybe a week at most depending on how complex a driver you want,your level of programming and how well you type.

b) pay someone to do the driver.Be prepared to supply 4-6 samples of the device and wait until it it done.How soon it gets done is directly proportional to the cash you're willing to pay.

option 'b' is easy

do option 'a' and you'll learn

rovtech · Joined: 24 Sep 2006 Posts: 262

I said graphics for dummies.
Is there software, what is GLCD?
I assume graphics is done as an x-y matrix but how are the arrays loaded?
How does one insert a character?
How does one get started?
It would be stupid to start programming in machine language and 'invent' an assembler only to find out that there are assemblers and compilers and MPLAB for free.
I have extensive experience in electronics hardware and am not too bad at C but I have never used a graphics display. I have used alpha-numeric LCD displays.

bkamen · Posted: Wed Mar 28, 2012 1:04 pm

temtronic · Posted: Wed Mar 28, 2012 6:11 pm

hmm.. graphics for Dummies. is a HUGE book though you seem to want a set of drivers for a specific GLCD.

GLCD means Graphics Liquid Crystal Display,at least to me.
The common 'text' or alpha-numeric LCD units are in fact a subset of GLCDs.They of course can be used for graphics though 'low resolution' or low pixel count compared to a 'graphics LCD'.

As for learning how to cut 'graphics' code,some of the best information was done 30 years ago for the TRS80s and Model100 computers.Very tight,efficient code written in BASIC none the less,with calls to small machine language subroutines.PSET,PCLR,PLINE,PCIRCLE,PCHAR were all 'commands' used back then.Even the IBM tehnical reference book has a wealth of graphical display information.

With respect to 'graphics for Dummies' you should specify what you need.First off monocolour or RGB display. Simple text..obviously easy, 'basic graphics' like circles,lines,rectangles, or multiple screens on one GLCD similar to 'Windows'.

rovtech · Joined: 24 Sep 2006 Posts: 262

Thanks for the helpful replies.
I bought a 128x64 LCD display, monochrome. There seems to be software that drives this from an Arduino but I am not about to abandon the PIC and CCS C (lazy).
I was hoping to get a link to someone's code that displays graphics on a similar LCD.
I would like to think that a function could be displayed. Say a straight line with slope and offset to start, or a sine wave.
For a complex colour display it seems easiest to just use an old laptop, however I want a lower resolution display for projects.
I started programming the Intel 8008 in machine language with programs on paper tape loaded by Teletype, and yes I know PIC assembly language. I have also programmed plots on the HP9820 calculator + plotter. However I am not a programmer, I prefer hardware.

W4GNS · Joined: 28 Sep 2010 Posts: 14 Location: Virginia, USA

rovtech · Joined: 24 Sep 2006 Posts: 262

To answer my own question so I may help others viewing this thread;
CCS has two routines as a starting point. They are graphics.c and GLCD.C and can be found in C:\progrm files\PICC\drivers if you have PIC C loaded on your computer. Also look in the \examples folder. I wish someone had pointed that out to me at the start.

What is needed as a starter for graphics is a function that plots a point and a function that draws a line between two points. These and several others are in these files.

If you know nothing about graphics then "Graphics primer for the IBM PC" Osborne/McGraw Hill ISBN 0-931988-99-3 is a good place to start. It is 1985 vintage but may be possible to find. It assumes a DOS system and BASICA but the descriptions and examples are applicable to modern graphics LCDs and can be adapted to C. You may even be able to find an old computer with Windows 3 and DOS with BASIC to try the examples.

There are programs in the CCS Code Library but they may cause confusion. If they don't include the CCS files but use functions beginning with GLCD_xxx then these are routines that are defined in that program and are not the CCS library functions. I can see a few reasons that one may want to write their own routines. The CCS routines seem to use quite a few ports (B, C, & D) but the LCD may have options such as serial, 4 or 8 bit communications. The 4 bit mode can do everything on one port with the other 4 bits used for the control (CS etc) bits. The CCS LCD.C does this for common alphanumeric LCDs.

I am not sure if a generic graphics program can be written since there are so many variables to the LCDs. Size, colour selection, built-in character generators, etc. This is another eason for a custom program.

bkamen · Posted: Fri Mar 30, 2012 10:23 am

rovtech · Joined: 24 Sep 2006 Posts: 262

I found example software in many places but almost all suffer from a lack of comments so it is very difficult for a novice to understand what is being done. The calling software was seldom included so it was impossible to determine which microprocessor was intended, or how to use the functions. Much of it was aimed at the Arduino and Atmel so the C was different from CCS C. What is worse it seems riddled with mistakes.
My display is the Digole 12864ZW module using the ST7920 connected to a PIC16F722.
I understand DDRAM, GDRAM, CGRAM, CGROM and HCGROM. OK, but how is each loaded. The Address Counter is a pointer to the address of all of these, but how do you know what is being addressed. I think it depends on the value loaded. I cannot find an overview of how the chip is used.
There are scary hints that individual pixels cannot be controlled, that the matrix is made up of 16x16 blocks, that the screen is split in two, and that only two of the four lines of characters can be used. All very confusing.
I have managed to get characters displayed but cannot get the welcome message displayed that is in HCGROM. I will post this progress separately.
Another example of a driver seems to need more than 1024 bytes of RAM on the PIC. This is to get around the problems by refreshing the screen from a cache. It looks like it might work but my 16F722 does not have enough RAM to compile. Why do the 16F chips have so little RAM? Can anyone suggest a PIC with 40 pins or less? Not surface mount.

rovtech · Joined: 24 Sep 2006 Posts: 262

I connected the Digole 12864ZW module to a PIC16F722 and got some functions working that INITIALIZE THE DISPLAY, WAIT FOR BUSY TO CLEAR, WRITE A COMMAND TO THE INSTRUCTION REGISTER, and WRITE TO THE DATA REGISTER. I can now display a character string.

I am unable to find working software. Can someone explain the following statements.

jeremiah · Joined: 20 Jul 2010 Posts: 1354

The "rom" means the values are placed into program memory and cannot be changed (as opposed to RAM, where most variables are located normally).

It looks like he is allocating an array of 4 values, which are the character positions command values of the 4 rows. To be honest, I don't know 100% sure the line you've posted will actually work, but I will assume it does (I don't typically allocate arrays that way).

The normal way you do that line is:

jgschmidt · Joined: 03 Dec 2008 Posts: 184 Location: Gresham, OR USA

Check out this article by Thomas Kibalo. He describes how to go about using a similar display and how to build a graphics and text library for it.

http://kibacorp.com/published-articles/nuts-and-volts-april-2010

This may give you some insight into how to proceed.
_________________
Jürgen
www.jgscraft.com

dezso · Joined: 04 Mar 2010 Posts: 102

rovtech · Joined: 24 Sep 2006 Posts: 262

Thank you for the replies. The Nuts&Volts article is interesting but it is for a different display. My friend has one of these (Digole) displays working with the Arduino and it seems to do the things others are having trouble with, including writing to a single pixel without having a large RAM cache. However the software is not well commented and is in Atmel C so it is hard to understand.
I don't think drawing to this display is as simple as mapping to x-y.
Perhaps dezso could explain exactly how one would do this - not the software, just explain the steps. Easier yet, how would one display the first character at address 80H in the CGROM? Why does the display go from line 1 to 3 to 2 to 4 with a long string? How do you start a new line? It does not respond to standard escape characters.
The software example I started with does not work with the Digole display but I am getting there. The scary things I mentioned may not be true. I can display 4 lines so I don't know what the spec sheet means by two lines of characters.
CCS has a (GLCD.C) driver for the HDM64GS12 display which is different from the ST7920. I suppose I could buy one and chuck mine but then I would not learn anything.
If I can get the basic drivers written then I can use the (graphics.c) CCS code to draw the graphics. I would like to keep this thread for the Digole display, or at least for the ST7920 driver chip.