Hi there
For your info
a null modem cable is a cable with crossover connections. ie the rx pin on one side goes to the tx pin on the other and vice versa.
pins 2 RX on side a to pin 3 TX on side b
pins 3 TX on side a to pins 2 RX on side b
pin 5 Signal groung on side a to pin 5 signal ground on side b
Also pins 7 to 8
pins 8 to 7
pins 6 to 4
pins 4 to 6
The term null moden means a cable connection without a modem . Modems in a modem connection oner a dial up connection would normally look after the rx to tx pins
Also when connecting a pc or laptop directly to the box network port Without a data switch then you must also use a network lead with crossover connections.
normal coulers used on a rj45 crossover network cable plugs are
pin 1rx Orange white --------------------\ /------------pin 1 rx Green white
pin 2 rx Orange ------\ /---------/-\------------pin 2 rx Green
pin 3 tx Green white --------\--/--------/ \-----------pin 3 tx Orange white
pin 4 blue white / \
pin 5 Blue / \
pin 6 tx Green -----/ \--------------------- pin 6 tx Orange
pin 7 Brown white
pin 8 Brown
pins 4,5 and 7, 8 are not used.
sorry my crossover drawing is not showing correctly on posts
hope this helps