Data type Range Default value
REG_DWORD 1 | 4 | 8 | 14 8


Determines the number of characters that can accumulated in the receive FIFO buffer of a National Semiconductor 16550-compatible device before it generates an interrupt. The device generates an interrupt when this threshold is reached or when an internal hardware timer expires. The hardware timer prevents characters from being left in the buffer when activity is low.

Increasing the value of this entry can improve the performance of the port. However, if the value is too high, the rate at which characters arrive in the buffer can exceed the rate at which they leave the buffer, resulting in overrun errors.

Note Image Note

The value of this entry is used as the default value for all serial ports on the computer. Settings for specific serial ports are stored in the device-specific subkey for that port in the Enum subkey (HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum).

Tip Image Tip

To change this value, you must edit the registry. To change the RxFIFO setting for a specific serial port, use Device Manager.

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