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Virtual COM Communications Issue

Question asked by jimfell on Mar 6, 2013
Latest reply on Jun 20, 2014 by Poul-Erik Hansen

I'm working on a Communications Device Class (CDC) driver for an embedded device, a Full Speed implementation of USB 2.0. The COM port settings are 115200, 8-bit, no parity, 1 stop bit, no flow control. Our PC application (32-bit, Windows 7, .NET 2.0) communicates with the target device through a virtual COM port, which on the target device can connect to either a FTDI (USB-to-SCI bridge) chip or the integrated USB peripheral in the microcontroller, depending on which port is selected by the application.


Both virtual COM ports work without any problems using Realterm. However, while our desktop application works using the virtual COM port connected via the FTDI chip, it hangs when attempting to use the virtual COM connected via the microcontroller's integrated USB peripheral.


When connected via the virtual COM port using the integrated USB, the application consistently hangs on the second call to SerialPort.Write(...). Using Serial Monitor from HHD Software I can see that the data is transmitted on the first call to SerialPort.Write(...). However, that data is never received by the target device.


It's odd because the only time I have seen similar problems on previous projects was when the flow control settings on each side of the bus were mismatched.


Here is the data captured from various port monitoring tools while running our PC application connected to the target device via its integrated USB peripheral. Any insight would be appreciated.


I am using CodeWarrior 10.2 with the MCF51JM128.  Any ideas or suggestions would be appreciated. Thanks.