User-contributed C Program for Serial Comms

C does not have built-in support for serial communication. Most programmers use hardware- and OS-specific libraries of serial I/O routines. One of our customers contibuted this standalone serial communication program for a DOS-based single-board computer. The program initializes comm ports and sends data without use of a serial comm library. It is designed to talk to our G12864 graphics LCD, but the principles are the same for virtually any serial device.

This program was compiled under Borland C++ V4.52.

If you need more in-depth information on serial comms under C, check with user groups that support your compiler, or follow some of the helpful links from Lakeview Research.

This information is offered as-is. Neither Scott Edwards Electronics, Inc. nor the author bear any responsibility for consequences arising from its use.

// This is a program that I cobbled together from various other programs to get my G12864 LCD to
// display text and bitmaps.  I also use it to control a keypad on COM2.  This is about as simple
// as it gets to control an LCD display and keypad.  Not all of the code was written by me.
// If you have a question about this code, e-mail me and I'll try and help out.  I can't guarantee
// that I'll be extremely helpful, but I can more than likely point you in the right direction
// go get things working properly.  

#include < stdio.h >    
#include < dos.h >      
#include < ctype.h >     

#define KEYINT 0x0016
#define GETKEY	0x010

int Port = 1;
int PortAddr = 0x03F8;
long int Speed = 9600;
int SpeedDiv = 12;
int EndFlag = 0;
int Port2Addr = 0x02F8;
int Ans;

// This routine initializes the COM1 port for the LCD display

PortInit()
{
	outp(PortAddr + 3, inp(PortAddr + 3) | 0x080);

	outp(PortAddr, SpeedDiv & 0x0FF);

	outp(PortAddr + 1, SpeedDiv >> 8);
	outp(PortAddr + 3, inp(PortAddr + 3) & 0x07F);

	outp(PortAddr + 4, inp(PortAddr + 4) | 0x003);
}

// This routine initializes the COM2 port for the keypad

Port2Init()
{
	outp(Port2Addr + 3, inp(Port2Addr + 3) | 0x080);

	outp(Port2Addr, SpeedDiv & 0x0FF);

	outp(Port2Addr + 1, SpeedDiv >> 8);
	outp(Port2Addr + 3, inp(Port2Addr + 3) & 0x07F);

	outp(Port2Addr + 4, inp(Port2Addr + 4) | 0x003);
}

// This routine shows a bitmap stored in EEPROM as image #2.  Each time something is written
// to the port, you must wait until the port is ready before sending any additional information
// or the port will not respond and transmit the data.

SendBmp()
{

	PortInit();

	for(int d = 0; d < 1; d++)
	{
		outpw(PortAddr, 27);
		while((inp(PortAddr + 5) & 0x020) == 0);
	}
	for(int a = 0; a < 1; a++)
	{
		outp(PortAddr, 69);
		while((inp(PortAddr + 5) & 0x020) == 0);
	}
	for(int b = 0; b < 1; b++)
	{
		outp(PortAddr, 50);
		while((inp(PortAddr + 5) & 0x020) == 0);
	}
	for(int c = 0; c < 1; c++)
	{
		outp(PortAddr, 32);
		while((inp(PortAddr + 5) & 0x020) == 0);
	}
}

// This routine displays 4 lines of text on the LCD.  Each text line is 16 characters long.

ShowScreen()
{
	char far * Line1 = "1 Calibrate     ";
	char far * Line2 = "2 Configure     ";
	char far * Line3 = "3 Diagnostic    ";
	char far * Line4 = "4 Run/Stop      ";

	int k;

	for (k = 0;k < 17;k++)
	{
		outp(PortAddr, Line1[k]);
		while ((inp(PortAddr + 5) & 0x020) == 0);
	}
	for (k = 0;k < 17;k++)
	{
		outp(PortAddr, Line2[k]);
		while ((inp(PortAddr + 5) & 0x020) == 0);
	}
	for (k = 0;k < 17;k++)
	{
		outp(PortAddr, Line3[k]);
		while ((inp(PortAddr + 5) & 0x020) == 0);
	}
	for (k = 0;k < 17;k++)
	{
		outp(PortAddr, Line4[k]);
		while ((inp(PortAddr + 5) & 0x020) == 0);
	}
}

// GetPortSel() is the code to get the value of a key press from a keypad.  The keypad is setup
// with a BASIC Stamp chip and BASIC Stamp code to return the ASCII values for the following
// keys:  1, 2, 3, 4, 5, 6, 7, 8, 9, 0, ENTER, A, B, C, D, BACKSPACE.  This code returns the
// value of the returned keypress to the calling routine.

GetPortSel(int Ans)
{
	Ans = 0;

	mark:

	Ans = inp(Port2Addr);
	if (Ans != 0)
	{
		outp(Port2Addr, 0);
		return(Ans);
	}
	else
		goto mark;

}

// Use SendData() to show a message on the scren and use a keypad to respond to the message.
// The keypad was set up to return an ASCII number based on which key was pressed.  The code
// resonds to the key pressed and shows displays the appropriate text.  I haven't included the
// ClearScreen(), ShowCalib(), ShowConfig(), ShowDiag(), ShowRunStop() becase they are the same
// as ShowScreen() with different text.

SendData()
{
	int i;

	PortInit();
	Port2Init();

	ShowScreen();

	switch(GetPortSel(Ans))
	{
		case 49:
			ClearScreen();
			ShowCalib();
			break;

		case 50:
			ClearScreen();
			ShowConfig();
			break;

		case 51:
			ClearScreen();
			ShowDiag();
			break;

		case 52:
			ClearScreen();
			ShowRunStop();
			break;

		default:;
	}
}

main(argc, argv, envp)
	int argc;
	char *argv[];
	char *envp;
{
		ShowBmp();	// only if you are showing a bitmap from EEPROM
		SendData();  // only if you are sending text to the LCD
}