Configuring a serial port

To change the settings for a serial port:

1. Start the Serial Manager.

2. Select the card from the ``Configured serial cards'' list, select the port from the ``Ports controlled by'' list, and then click on the Modify button next to the Ports list.

   ---

   NOTE: You cannot select a serial port that has a mouse or other pointing device attached.

   ---

3. You can change the information for any of the following fields:

   
   Speed (bps)

   Select the default speed for the serial port. The selected speed should not be greater than the capabilities of the UART (universal asynchronous receiver/transmitter) chip that controls the port. ``Serial port speeds, line-mode labels, and UART limitations'' shows how the maximum speed is limited by the capabilities of the UART hardware.

   Serial port speeds, line-mode labels, and UART limitations

   Speed	Line-mode	Limitations
   (bps)	label	of UARTS
   1200	2
   2400	3
   9600	m or 6	Highest speed for 8250
   19200	n	Highest speed for 16450 when used with fast modems
   38400	o
   57600	p
   115200	r	Highest speed for 16450 and 16550-or-better
   230400	s
   460800	t
   921600	u
   1382400	N/A

   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:

   UART	FIFO size
   8250, 16450	1 byte
   16550	1 byte
   16550A	16 bytes
   16650	1 byte
   16650V2	32 bytes
   16654, 16750	64 bytes
   1685x	128 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:

   • The speed limitations shown may be too high for heavily loaded systems that cannot react quickly enough to move data from the UART's receive buffer.

   • If the system cannot keep up with serial data reception, data will be lost. Run the sar(ADM) command with the -g option to see if you are experiencing serial buffer overruns.

   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.

   
   Line-mode label

   Click on Change to change the line mode for the serial port. Select a line-mode label from the list displayed and click on OK to confirm.

   ---

   NOTE: You cannot change the line mode if it is the only one that is defined for the currently selected line speed.

   ---

   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.

   
   Login/Answer

   Select On to enable a login on the port. Select Off to prevent anyone logging in.

   
   Receive buffer

   Adjust the slider bar to select the desired setting. Select a lower value if characters are being lost in incoming data. Select a higher value to improve system performance by reducing the number of interrupts that the serial port generates. See ``Changing the interrupt trigger level'' for more information.

   ---

   NOTE: Some UARTs only allow a few specific values for the Receive buffer. If you select a setting that isn't supported, the Serial Manager automatically picks the next lowest value that is supported by the UART. To see what the actual setting is, modify the port again and check the value in this field.

   ---

   
   Transmit buffer

   Adjust the slider bar to select the desired setting. Selecting a lower value may improve performance by reducing the number of interrupts that the serial port generates. Selecting a higher value may improve serial throughput by reducing the chance that there will be periods where the serial port's transmit buffer is empty (and the serial line idle), even though an application has data to send. See ``Changing the interrupt trigger level'' for more information.

   ---

   NOTE: Some UARTs only allow a few specific values for the Transmit buffer. If you select a setting that isn't supported, the Serial Manager automatically picks the next lowest value that is supported by the UART. To see what the actual setting is, modify the port again and check the value in this field.

   ---

4. Click on OK to confirm.

5. Click on Close.

   ---

   NOTE: If the Serial Manager relinks the kernel because you changed the configuration of the serial ports, you must shut down and reboot the system for the changes to take effect.

   ---