RS422I-PA Manual
Page 5-2
Manual 00650-519-1
Baud
Rate
Divisor
X1
Divisor
X4
Notes
Max. Diff’l.
Cable Length*
460800
N/A
1
230400
N/A
2
153600
N/A
3
115200
1
4
375 ft.
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 commonly used in industry
4000 ft.
4800
24
96
4000 ft.
2400
48
192
4000 ft.
1200
96
384
4000 ft.
*These are theoretical maximums based on typical conditions and good quality cables.
Table 5-1:
Baud Rate Divisors
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 A3. 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 zeroes.
Bit 7 is the DLAB discussed earlier. It must be set to zero after the divisor is loaded or else
there will be no communications.