Article ID: 010307sab
Last Reviewed: December 22, 2025
The information in this article applies to:
Symptoms
Pronto for Windows produces the error message during download:
Overrun error: Character received, but not processed before the next character arrived.
Cause
This problem is caused by the Windows serial driver failing to collect a character from the serial port before another one arrives and overwrites it, causing it to be lost.
Resolution
On Windows 7 / 8 / 10 / 11
A solution is as follows:
- search for and open DEVICE MANAGER
- select PORTS
- select the COM port that is being used
- click on PROPERTIES
- click on PORT SETTINGS tab
- click on ADVANCED
- Reduce the setting for the Receive Buffer (move it to the left).
- click on OK
- click on OK
Typically it is only necessary to move the setting one division to the left but some device drivers may ‘hog’ the processor requiring further reduction. Using a lower setting reduces processor performance very slightly (a couple of percent). Note that changes made to this setting only take effect after a reboot.
Windows 2000 / XP / Vista legacy information
The solution above applies but access to DEVICE MANAGER is as follows:
- open (MY) COMPUTER
- open CONTROL PANEL
- open SYSTEM
- click on DEVICE MANAGER tab
Windows NT4 legacy information
On Windows NT4 the receive buffer setting can only be changed using the registry editor, this setting is stored under the key:
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Serial]
In the value:
“RxFIFO”=dword:00000008
In Windows NT4 the default is 8, change this setting to 4 or 1 to reduce the incidence of overrun errors. Note that changes made to this setting only take effect after a reboot.
Historical notes on systems from circa 2000
Some early pentium laptops had a different sort of COM port called a 8250 as opposed to the current 16550.
On these machines the adjustment above is not available and the only solution is to try one or more of the following:
- Close applications that consume processor time.
- Turn off power management and / or screen savers during download.
- Reduce the baud rate.
- Buy an after-market plug in card with the new sort of COM port.
Computers affected by this problem will almost certainly suffer the same errors in other communication packages. If it occurs rarely it will be masked by the automatic retry process in most modern e-mail and terminal programs.