VISA and Hyperterminal send the same characters. What might be different is the communication parameters (i.e. baud rate, parity, etc.) or you might not be sending a termination character. See if the processor needs a LF or CR at the end of the command in order to process it. If it does, add the control character to the end of your string. You can do this by using the concantanate string function and the character from the string palette or using a VISA Property node (i.e. VISA Configure Serial Port) to automatically add a term character to each write.