Kontron 104-422-2I, Руководство пользователя

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5-4
104-422/485-2I User’s Guide
See the documentation for your chosen language for details.
Under DOS, the process is very different. The remainder of this chapter describes DOS
programming.
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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 A3. In C code, the call would be:
outportb(BA3,0x80);
You then load the divisor into Base A0 (low byte) and Base A1 (high byte). The
following equation defines the relationship between baud rate and divisor:
desired baud rate = (crystal frequency) / (32 * divisor)
The UART clock frequency is 1.8432MHz. The following table lists popular divisor frequencies.
Table 5-2. Baud Rate Divisors
Baud Rate Divisor (X1) Notes Max. Diff’l.
Cable Length*
460800 N/A 500 ft.
230400 N/A 800 ft.
153600 N/A 1300 ft.
115200 1 2200 ft.
57600 2 4000 ft.
38400 3 4000 ft.
28800 4 4000 ft.
19200 6 4000 ft.
14400 8 4000 ft.