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Page 5-1
Manual MPCICOM422-4.E1b
Chapter 5: Programming
Sample Programs
There are sample programs provided with the PCI-COM422/4 card in C, Pascal, QuickBASIC, and
several Windows languages. DOS samples are located in the DOS directory and Windows samples
are located in the WIN32 directory.
Windows Programming
The PCI-COM422/4 card installs into Windows as COM ports. Thus the Windows standard API
functions can be used. In particular:
? CreateFile() and CloseHandle() for opening and closing a port.
? SetupComm(), SetCommTimeouts(), GetCommState(), and SetCommState() to set and change
a port’s settings.
? ReadFile() and WriteFile() for accessing a port.
See the documentation for your chosen language for details.
Under DOS, the process is very different. The remainder of this chapter describes DOS programming.
Initialization
Initializing the chip requires knowledge of the UART's register set. The first step is to set the baud
rate divisor. You do this by first setting the DLAB (Divisor Latch Access Bit) high. This bit is Bit
7 at Base Address +3. In C code, the call would be:
outportb(BASEADDR +3,0x80);
You then load the divisor into Base Address +0 (low byte) and Base Address +1 (high byte). The
following equation defines the relationship between baud rate and divisor:
desired baud rate = (UART clock frequency) / (32 * divisor)