Communications Timeout (Serial Port, Windows 95/98/Me)

If you use serial port communications with a Windows 95, 98, or Me and the Multiple Master PPI Protocol setting, you may experience communications timeouts. (Timeouts are not common with the Single Master PPI Protocol setting but are theoretically possible.) The timeouts can occur when your FIFO Receive Buffer setting is not low enough. This setting is not controlled by STEP 7-Micro/WIN 32, but you can access and correct it from Windows.


If the Communication Setup window displays device icons with question marks instead of correctly identifying the devices on your network, that is a symptom of a communications timeout, and can be corrected using the procedure below.

To adjust your FIFO Receive Buffer setting and prevent communications timeouts, follow the steps below.

1.From the Windows desktop, right-click the My Computer icon and choose the Properties menu item.

2.From the System Properties dialog box, select the Device Manager tab.

3.From the Device Manager tab, locate and double-click the Ports icon.

4.From the expanded Ports branch, locate and double-click on the Communication Port icon that represents the COM port that you are using for STEP 7-Micro/WIN 32.
(You can physically identify the correct COM port by examining the cable connection at the back of your PC or programming device. The COM port selection that you made when setting up communications in STEP 7-Micro/WIN 32 must match the COM port being used on your PC or programming device. For information about making a COM port selection for STEP 7-Micro/WIN 32 communications, see Selecting and Changing Parameters.)

5.From the Communication Port Properties dialog box, choose the Port Settings tab.

6.From the Port Settings tab, click the "Advanced" button.

7.At the Advanced Port Settings dialog box, examine the checkbox for "Use FIFO Buffers." Make sure there is a check mark in the box.

8.Examine the slider for Receive Buffer. If it is not at the lowest possible setting (1), move it to the lowest setting.

9.Choose OK to confirm your selections and close the open dialog boxes.

After you follow this procedure, you should no longer receive communications timeouts.


If this solution does not correct your timeout problems, try closing down other network applications, or change your STEP 7-Micro/WIN 32 communications protocol setting from Multiple Master to Single Master.