Settings for the 16550 UART FIFO Buffer

This article was previously published under Q131016
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This article describes the FIFO settings for a 16550 UART chip and how tochange them.
Windows 95 provides two methods for accessing the 16550 UART FIFO buffersettings. Each method is a global setting and can affect PCMCIA, internal,and external modems. Use one of the following methods to access theAdvanced 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.
NOTE: This setting can be changed from any modem properties dialog box.If you change this setting in one connectoid, it affects all connectoids.

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.
In the Advanced Port Settings dialog box you can:
  • 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 FIFObuffers (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 decreasethis value, more interrupts are sent to the processor, slowing bytes intothe UART. If you increase this value from 8 to 14, characters may overrunthe 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 of16. If you decrease the buffer from 16, more interrupts are sent to theprocessor, slowing down the rate at which bytes are sent into the UARTTransmit buffer, reducing serial overruns. The higher the number, thefewer interrupts are sent, increasing system performance during uploads.

Article ID: 131016 - Last Review: 12/04/2015 11:27:28 - Revision: 1.1

Microsoft Windows 95

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