<P> This cable could be used with more software but it had no actual enhancements over its predecessor . The software would work thinking it had hardware flow control but could suddenly stop when higher speeds were reached and with no identifiable reason . </P> <P> In this cable the flow control lines are still looped back to the device . However, they are done so in a way that still permits Request To Send (RTS) and Clear To Send (CTS) flow control but has no actual functionality . The only way the flow control signal would reach the other device is if the opposite device checked for a Carrier Detect (CD) signal (at pin 1 on a DE-9 cable and pin 8 on a DB - 25 cable). As a result only specially designed software could make use of this partial handshaking . Software flow control still worked with this cable . </P> <P> This cable is incompatible with the previous types of cables' hardware flow control, due to a crossing of its RTS / CTS pins . With suitable software, the cable is capable of much higher speeds than its predecessors . It also supports software flow control . </P> <P> A virtual null modem is a communication method to connect two computer applications directly using a virtual serial port . Unlike a null modem cable, a virtual null modem is a software solution which emulates a hardware null modem within the computer . All features of a hardware null modem are available in a virtual null modem as well . There are some advantages to this: </P>

9 pin to 9 pin null modem cable pinout