PC Hardware in a Nutshell, 3rd Edition

Configuring COM port settings in Windows NT 4

To configure port settings in Windows NT, run the Control Panel Ports applet. The Ports dialog lists the COM ports that NT recognizes. Double-click the port to be configured and use the drop-down lists in the Settings dialog, shown in Figure 22-9, to configure default port settings for speed, framing, and flow control.

Figure 22-9. The Windows NT 4 Settings dialog, where you configure communication parameters for the port

To view or change settings for I/O port and IRQ, click the Advanced button in the Settings dialog, and use the drop-down lists to specify parameters for the port (see Figure 22-10). You can enable or disable FIFO buffering by marking or clearing the checkbox, but Windows NT 4 makes no provision for tuning FIFO performance from the GUI. Although it’s probably not worth the time to do, you can modify FIFO buffering settings using the Registry Editor. FIFO settings are contained in the key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Serial. The relevant value entries are:

RxFIFO

The RxFIFO value entry specifies the number of bytes that must accumulate in the receive FIFO buffer before a COM port interrupt is triggered. RxFIFO is a REG_DWORD value. The default value for this entry is the value set for the Serial service, which is eight bytes.

TxFIFO

The TxFIFO value entry specifies the number of bytes that must accumulate ...