11.7 Connector and Adapter Types
A connector is more-or-less permanently attached to the end of a cable or to a hardware unit. There are two basic types of connectors used in serial communications: 1. DB types with pins (DB 9 or DB25) and 2. modular telephone-style connectors.
An adapter looks about like a connector but it has two ends with pins. It is just like a cable that is so short that there is no cable part left at all --just different connectors on each end is all that remains. The adapter just plugs in to two other connectors on each side of it. It allows two incompatible connectors to mate with each other by going in between them. Except that even for two connectors that will mate with each other, an adapter may be used to connect the cable conductors together in other than straight-thru. Obviously, one may use a special cable (perhaps homemade) as a substitute for an adapter.
Sex of connector/adapters
Connectors (or one side of adapters) are either male or female. The connectors that have pins are male and the ones that have sockets (sometimes also called pins) are female. For modular connectors, the ones with exposed contacts are plugs while the ones with internal contacts (not easy to see) are jacks. Plugs are male; jacks are female.
Types of adapters
There are three basic types of adapters: null modem, gender changers and port adapters. Some adapters perform more than one of these three functions.
- null modem adapter: Reroutes wires, like a null modem cable.
- gender changer: Changes the sex of a cable end. Two connectors of the same sex can now connect (mate) with each other.
- port adapter: Goes from one type of connector to another (DB9 to DB 25, etc.)
DB connectors
(For how to install a DB connector on the ends of a cable see Installing DB Connectors.) These come in 9 or 25 pins. The EIA-232 specs. call for 25 pins but since most of these pins are not used on ordinary serial ports, 9 pins is sufficient. See DB9-DB25 for the pin-out. The pins are usually numbered if you look closely enough or use a magnifying glass.
RJ modular connectors
RJ means Registered Jack. These look like modern telephone connectors but are sometimes not compatible with telephone connectors. See also Installing RJ Connectors. For use with serial ports they may be 6 or 8 conductor. A few are 10-conductor but may not officially belong to the RJ series.
6-conductors: RJ11/14, RJ12, and MMJ
RJ11 are all the same size but may have 2, 4, or 6 conductors. If it has two conductors, it should be called a RJ11. If it has 4 conductors, some call it a RJ14. If it has 6 conductors, many call it a RJ12 (but a RJ12 per the phone company has only 4 conductors). Seems confusing but they are all the same size and differ mainly by the number of conductor contacts present.
A look-alike (almost) is a MMJ connector (6-conductor) used on later model VT (and other) terminals. It's sometimes referred to as a DEC-423 or a DEC RJ11. MMJ has an offset tab and is not compatible with RJ ones (unless the tab is cut off). However, some connectors have been made that are compatible with both MMJ and the RJ ones. Since MMJ connectors are both hard to find and may be expensive some people have forced a RJ (6 conductor) to fit MMJ by filing off the offset tab with a file.
The MMJ (DEC) pinout is: 1-DTR, 2-TxD, 3-TxD_Gnd, 4-RxD_Gnd, 5-RxD, 6-DSR. Cyclades Cyclom-8Ys RJ12 has: 1-DTR, 2-TxD, 3-Gnd, 4-CTS, 5-RxD, 6-DCD. Specialix IO8+ has: 1-DCD, 2-RxD, 3-DTR/RTS, 4-Gnd, 5-TxD, 6-CTS. The pins of the RJ (and MMJ) are numbered similar to the RJ45.
[blockquote shade=yes][/blockquote]
Plug Jack (or socket)
(Looking at the end (Looking at the cavity
end of a cable) in a wall or PC back)
.________. .________.
| 654321 | | 123456 |
|__. .__| |__. .__|
|__| |__|
A standard
* License
