FTDI VCP Problem read

[jmc90]

Hi,

I´ve designed an aplication based in the example of "Multithread_serial" that reads packet of 120bytes data transfered every 20ms over a specified Serial COM port. This COM port is "emulated" by the FT232R of FTDI which recives the data from a MSP430 , in serial way (Tx and Rx), and the PC access it as a VCP. The probem is that most of times i recieve data with a missing packet or signal or with very high "glitches" like this:

No matter if i set the COM speed to a lower value, i´ve tried with 230400 Baud first, after 115200, 57600, reducing the size of paket (60bytes), and the time between pakets to 80ms, and the problems were still there, i set a lower latency value os the COM port and nothing changed. Most rare thing is that one time in a 100 the system seems to work properly, with the same settings: pakets of 120bytes every 20ms at 230400 baud. (The first part of this singal its not periodic because it was updating):

 

If anyone has any idea of what is happening it would be really helpfull, i think maybe its a problem with FTDI drivers, im using the version 2.08.30 for Windows (downloaded from FTDI web page), and Windows 8.1

[Intaris]

Have you verified the effectiveness of the shielding on your cable? Try to make sure its only connected to ground on one side of the cable.

[mikeporter]

Is there anything that is distinguishable about the packets generating the spikes? Do the packets include check sums or CRC that you can use to verify their validity?

Mike...

[jmc90]

Thanks for your response, this is the scheme of the system, i´ve skipped the ADC stage by connecting directly uC to the Ft232R for testing only the serial com. and i´m generating a square signal in the MSP430, and converting it with the same Labview application.

[Intaris]

I see two ground connections.

Are you sure you don't just have a ground loop?

You should make sure that you don't have a circular ground connection, making sure the serial cable isgrounded only ont he side of the PC would be a good place to start.