User manual

Chapter 5: Programming

There are sample programs provided with the 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.

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)

When the BAUD jumper is in the X1 position, the UART clock frequency is 1.8432 Mhz. When the

jumper is in the X4 position, the clock frequency is 7.3728 MHz. The following table lists popular

divisor frequencies. Note that there are two columns to consider depending on the position of the

BAUD jumper.

Baud Rate Divisor x1 Divisor x4 Max Diff. Cable Length*

460800 - 1 550 ft

230400 - 2 1400 ft

153600 - 3 2500 ft

115200 1 4 3000 ft

57600 2 8 4000 ft

38400 3 12 4000 ft

28800 4 16 4000 ft

19200 6 24 4000 ft

14400 8 32 4000 ft

9600 12 48 – Most Common 4000 ft

4800 24 96 4000 ft

2400 48 192 4000 ft

1200 96 384 4000 ft

* Recommended maximum distances for differentially driven data cables (RS422 or RS485) are for typical conditions.

Table 5-1: Baud Rate Divisor Values

In C, the code to set the chip to 9600 baud is:

outportb(BASEADDR, 0x0C);

outportb(BASEADDR +1,0);

Manual PCI-ICM-422(485)/2(4)