Settings for the 16550 UART FIFO Buffer

• Microsoft Windows 95

SUMMARY

This article describes the FIFO settings for a 16550 UART chip and how to change them.

MORE INFORMATION

Windows 95 provides two methods for accessing the 16550 UART FIFO buffer settings. Each method is a global setting and can affect PCMCIA, internal, and external modems. Use one of the following methods to access the Advanced Port Settings dialog box:

Method 1

1. Click the Start button, point to Settings, then click Control Panel.

2. Double-click Modems.

3. On the General tab, click Properties.

4. On the Connection tab, click Port Settings.

Method 2

1. Click the Start button, point to Settings, then click Control Panel.

2. Double-click System.

3. On the Device Manager tab, double-click Ports (COM & LPT).

4. Double-click the communications port (COMx) you want to change.

5. On the Port Settings tab, click Advanced.

• Enable/disable the FIFO buffer for the 16550 chip.

  NOTE: The COMxFIFO setting that can be manually added to the [386Enh] section of the SYSTEM.INI file does not affect Windows-based programs in Windows 95. This setting only affects MS-DOS-based programs.

• Increase/decrease the Receive buffer.
• Increase/decrease the Transmit buffer.

Enable/Disable the FIFO Buffer

To disable the FIFO buffer for a 16550 UART chip, click the "Use FIFO buffers (requires 16550 compatible UART)" check box to clear it.

Receive Buffer

The Receive Buffer slider supports the values 1 (low), 4, 8, and 14 (high).

The default value of 8 should be sufficient in most cases. If you decrease this value, more interrupts are sent to the processor, slowing bytes into the UART. If you increase this value from 8 to 14, characters may overrun the FIFO buffer.

Transmit Buffer

The Transmit Buffer slider supports the values 1 (low), 6, 11, and 16 (high).

If you experience problems uploading files, decrease the default value of 16. If you decrease the buffer from 16, more interrupts are sent to the processor, slowing down the rate at which bytes are sent into the UART Transmit buffer, reducing serial overruns. The higher the number, the fewer interrupts are sent, increasing system performance during uploads.