I have a linear actuator which can run on Modbus serial communication protocol. By default, the device is in a digital communication mode. To enable the serial communication in hyperterminal, I disable the connection port; set up the parameters; hit "call"; turn the device on; then I can send a command massages to enable the serial communication. Then I can send any command in hyperterminal to control the device. I suppose anything that hyperterminal can do, Labview can do it too. I've tried some hyperterminal mimic VIs downloaded from here but they all did not have the "call" function built-in. A simple VISA write/read program also did not work. I assume that a "call" function in hyperterminal is just to send contiguous signals to the device (I only have one slave to control). I just do not know what signal and how it works. Any help or any example Vi will be highly appreciated. Thank you!