To change the settings for a serial port:
Serial port speeds, line-mode labels, and UART limitations
|9600||m or 6||Highest speed for 8250|
|19200||n||Highest speed for 16450 when used with fast modems|
|115200||r||Highest speed for 16450 and 16550-or-better|
The table shows the highest speeds that can be used with ports controlled by the various supported UARTs on normally loaded systems. The specification for the 16450 chip allows it to run at speeds of up to 115,200bps when used with terminals and printers. It is unreliable at speeds over 19,200bps when used with high-speed modems because it does not have a receive buffer. The 16550 has a 16-byte receive buffer that allows it to be used with modems at speeds up to 115,200bps. Ports that are controlled by 16550x, 16650x, 16654, 16750, and 1685x UARTs can be used for any purpose, typically at speeds up to 115,200bps. Note that some 16550-or-higher UARTs may support higher speeds.
The larger the FIFO size for the UART, the higher a rate of speed you will be able to use without experiencing serial buffer overruns. The following table lists the FIFO sizes for the UARTs supported in SCO OpenServer:
|8250, 16450||1 byte|
|16654, 16750||64 bytes|
Any other UARTs are treated as an 8250 chip, with a 1-character FIFO.
Note that the speeds listed here are subject to the following hardware limitations:
To determine the type of UARTs your computer uses, run hwconfig(C) and examine the command's output. For each serial board, you should see a line like this:
name=serial base=0x2F8 offset=0x7 vec=3 dma=- unit=1 type=Standard nports=1 base=8 16550A/1
In this example, the UART is a 16550A.
The ``line mode'' determines the default characteristics of the serial port such as parity, and number of bits per character. Each line-mode label corresponds to a separate entry in /etc/gettydefs. ``Serial port speeds, line-mode labels, and UART limitations'' shows commonly used line-mode labels for each speed. See ``Installing serial terminals'' and the gettydefs(F) manual page for more information.