If the device is set up for hardware handshaking, you cannot simple cut the wires. Here is how hardware handshaking works. I will call the Labview end as the computer, and the Cygnus as the device. If the device is setup for hardware handshaking, it will only send its data when it sees the CTS line high. I'm not sure which pin this is, you can look it up in the Cygnus manual. When the device wants to send data, it raises the RTS line (Request To Send). The computer sees this, and if it is ready to accept data, it raises the CTS line (Clear To Send). Then the device sends its data.
Lets say that the device is sending so much data, or at a high rate, that the computer cannot handle it fast enough. Normally that would cause a buffer overrun, and data would be lost. With handshaking, the computer end would know that it is running out of buffer space, and it would lower the CTS line. The device would see this and it would stop sending data. Then the computer has a chance to process the data, empty its buffer, then it would raise CTS again, resulting in the device sending more data. This continues until all data is sent, and the device drops the RTS line.
If the device requires hardware handshaking, and you don't want to use it, you can wire the RTS and CTS lines together at the device end. But this could result in loss data. Also, if using handshaking, the computer end must also be set up to produce the handshaking. I believe this is a parameter setting in the Serial Initilaize VI.
Since you are losing data, and since you must operate at a speed much slower than the device specs, you may have a bad cable. The cable should be shielded or you may have external interference, causing loss of data and forcing you to run at slower speeds. The shield should be grounded at the computer end only. Grounding at both ends could cause a ground loop, resulting in more interference. The wires inside the cable should be twisted pair to minimize the crosstalk between Tx and Rx. Use one wire out of a twisted pair for Tx, and the other wire out of the twisted pair to ground. Use a different twisted pair for Rx and Ground. This is not very important for very short cables, but the longer the cable, the more important it becomes. With extremely long cables, you may have to terminate the device end for the Tx line with a 100 ohm resistor to ground, and terminate the computer end for the Rx line with a 100 ohm resistor to ground. This eliminates reflecting waves. Termination is especially true when using flat ribbon cables of lengths longer than a few feet.
Just thought of something else. You say that after a while the data becomes corrupt. This is a classic example of buffer overruns. The computers (or the devices) input buffers start filling up faster than the computer can process the data. It my fill up very slowly if the processing rate is almost equal to the device sending rate. But after a while, the buffer becomes full, and any extra data coming in before the buffer is read will be lost. After that, more data will be lost quite often, resulting in corrupt data. This is why handshaking is so important. In most cases, the computer can process the data faster than the device can send it, and no handshaking is required. But your case may be different. Maybe you need the handshaking.
I hope you can find your problem using something I said.
