Start • P Is For PC/104 • Easy PIC Video • MC104P Functions • Be A Hero • Sources and PDF

EASY PIC VIDEO

One of the real eye catchers at the MASTERs Conference was the MC104P driving the flat panel PC display. The video hardware behind the spectacle is shown in Photo 2. Calmotion provides a video library for VGA cards that employ a GD542X chipset like the one shown in the photo. The Calmotion video library was built using Microchip’s C18 C compiler librarian utilities.

(Click here to enalrge)

Photo 2—What you see here is a standard PC/104 video card. It looks like this one may have come from Arcom.

Using the video library’s functions is simple. Simply incorporate the calmotion_video.lib library in your project. Call the four video functions in the library as you need them.

There’s another file that you must fold into the project. The calmotion_MCP104P.lib library file contains MC104P hardware initialization routines and other functions that enable you to move data in the MC104P memory and I/O areas covered in Figure 1.

For now, let’s concentrate on the MC104P video library and examine the code in Listing 1, which generated the image shown in Photo 3. I’ve shown the code behind the #include “pc104.h” statement. As you can see, this C include statement contains prototypes of the functions contained in the calmotion_MCP104P.lib and calmotion_video.lib libraries. Flowing down just before the main function are definitions for row, column, foreground, and background. These character definitions are merely placeholders for arguments that will be used in some of the video function calls. The col and the x are used in the letters.c function calls. A typical function to form a letter is shown at the bottom of Listing 1.

(Click here to enlarge)

Photo 3—This shot was inspired by my old mainframe experiences. I was tapping keys on those old glass terminals long before my hands even touched a PC keyboard.

The video display area is composed of 25 rows and 80 columns. The locate function uses row and column values to position the cursor on the screen. A value of zero for either the row or column values doesn’t alter the current row or column setting. Issuing a call to the locate function in this manner, locate(1,1) positions the cursor at the top left of the display. The locate(25,80) statement places the cursor at the bottom right corner of the display. That’s simple enough.

The color function uses foreground and background variables. Eight shades of grey and the primary colors found in any box of Crayola crayons can be mixed and matched as foreground and background screen colors. For instance, the color(0x07,0x00) statement produces white characters against a black background. Calmotion provides sample video code that displays all of the possible foreground and background color combinations.

The first function call in Listing 1 is made to code contained within the calmotion_MCP104P.lib file. The init_mc104p function initializes all of the hardware peripherals and sets up the PC/104 bus. The MC104P’s hardware peripherals include the board’s digital I/O ports, the analog inputs, and any user LEDs that may be on the MC104P PCB. This type of function is found in the firmware of numerous SBC modules. As you can see in this case, it’s usually a good idea to run a function like this right off the bat.

The video functionality provided by the add-on PC/104 card begins with a call to the init_cirrus_video function. This function initializes the VGA foreground and background color attributes. Also, the init_cirrus_video function redirects the standard I/O so that the C language printf functions write to the video display instead of the PIC’s USART. If you need to revert stdout to the USART, just code stdout = _H_USART. The stdout = _H_USER C statement will redirect standard I/O to the video card. As the cls clear screen function executes, you’ll realize just how easy putting up a PC-like alphanumeric video image using the MC104P is going to be.

The remainder of this little piece of video demonstration code in Listing 1 sets up the foreground and background colors and places the cursor initially at the home position (1, 1) in the upper left corner of the display. I used the locate function in conjunction with the printf function in the letters.c function set to paint the display shown in Photo 3.