Frequently Asked Questions

What does a NULL Modem cable look like?
Last Updated 4 years ago

Only the wires 2, 3 and 5 in the null modem cable has to be connected as the figure shows:
(There is no physical handshake).

Signal Name

DB-25 Pin

DB-9 Pin

 

DB-9 Pin

DB-25 Pin

 

FG (Frame Ground)


-

X

-


FG

TD (Transmit Data)


3

-

2


RD

RD (Receive Data)


2

-

3


TD

RTS (Request To Send)



-



CTS

CTS (Clear To Send)



-



RTS

SG (Signal Ground)


5

-

5


SG

DSR (Data Set Ready)



-



DTR

CD (Carrier Detect)



-



DTR

DTR (Data Terminal Ready)



-



CD

DTR (Data Terminal Ready)



-



DSR


If there still are transmission problems there is one more action to do:

To be really sure that the ground point is the same for both the car and trailer, there has to be a connection between

the minus(-) pole on the trailers battery to the chassis of the car (any point of chassi metal on the car  where you can connect a wire)


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