Frequently Asked Question
What does a NULL Modem cable look like?
Last Updated 11 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)