User manual

ICOM-2S Manual
5-2
Manual MICOM-2S.Eb
On the ICOM-2S card, the clock frequency to the UART is 1.843 MHz. Below is a table for the
popular divisor frequencies:
Baud Rate Divisor Notes Approx Max Cable
length *
115200 1 2200 ft
57600 2 High-speed opto-couplers required 4000 ft
38400 3 Maximum speed for standard opto-couplers 4000 ft
28800 4 4000 ft
19200 6 4000 ft
14400 8 4000 ft
9600 12 4000 ft
4800 24 4000 ft
2400 48 4000 ft
1200 96 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(BASEADDR +1,0);
The second initializing step is to set the Line Control Register at Base Address +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 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.