PCI-RS422 Manual
Page 5-2
Manual 00650-521-1
Baud Rate
Divisor
x1
Divisor
x4
Notes
Max Diff. Cable Length *
460800
N/A
1
230400
N/A
2
153600
N/A
3
115200
1
4
375 feet
57600
2
8
660 ft
38400
3
12
920 ft
28800
4
16
1165 ft
19200
6
24
1620 ft
14400
8
32
2050 ft
9600
12
48
Most common industrial
speed
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(BA1,0);
The second initializing step is to set the Line Control Register at Base A 3. This register
defines word length, stop bits, parity, and the DLAB. Bits 0 and 1 control word length and allow
word lengths from 5 to 8 bits. Bit settings are extracted by subtracting 5 from the desired word
length. Bit 2 determines the number of stop bits. There can be either one or two stop bits. If Bit 2
is set to 0, there will be one stop bit. If Bit 2 is set to 1, there will be two stop bits. Bits 3 through
6 control parity and break enable. They are not commonly used for communications and should be
set to zero. Bit 7 is the DLAB discussed earlier. It must be set to zero after the divisor is loaded
or else there will be no communication.
