RS-232, 10base-T, 100-baseTX, ethernet, DCE, DTE, cables, pinouts, and related info
Entries are in alphabetical order.
568A: 568A is the ethernet equivalent of DCE. The wiring usually
used on hubs, routers, patch panels, etc.
| pin | EIA/TIA std 568A: | pin | notes |
| 4 | blue / blue on white | 5 | central pair |
| 6 | orange / orange on white | 3 | just outside central pair |
| 2 | green / green on white | 1 | "left" pair |
| 8 | brown / brown on white | 7 | "right" pair |
See also RJ-45 connector.
568B: 568B is the ethernet equivalent of DTE. The wiring used on
ethernet cards.
| pin | EIA/TIA std 568B: | pin | notes |
| 4 | blue / blue on white | 5 | central pair |
| 2 | orange / orange on white | 1 | "left" pair |
| 6 | green / green on white | 3 | just outside central pair |
| 8 | brown / brown on white | 7 | "right" pair |
See also RJ-45 connector.
braided: braided see flex.
cat-3: Category 3 and Level 3 are the same, they refer to the
older UTP cable used for ethernet. Cat-3 cable is rated for use at 10 Mbps.
cat-4: Category 4 and Level 4 are the same, they refer to the
UTP cable used for Token Ring. Cat-4 cable is rated for use at 20 Mbps.
cat-5: Category 5 and Level V are the same, they refer to the
UTP cable used for ethernet. Cat-5 cables came into common use during 1996 and are rated for use at 100 Mbps. The older types are Category 3 and Category 4.
cat-6: Category 6
UTP cable is rated for speeds up to 250 Mbps.
cat-7: Category 7
UTP cable is rated for speeds up to 600 Mbps.
crossover-cable: A crossover cable or crossover patch cable is
the equivalent of a null-modem cable, a cable that connects two pieces of equipment whose connectors are the same (same signals in the same place). If all connectors were wired the same, crossover cables would be the only type anyone would need. A crossover patch cable is wired like this:
| 568B End | 568A End |
| 1 orange on white | 1 green on white |
| 2 orange | 2 green |
| 3 green on white | 3 orange on white |
| 4 blue | 4 blue |
| 5 blue on white | 5 blue on white |
| 6 green | 6 orange |
| 7 brown on white | 7 brown on white |
| 8 brown | 8 brown |
See also straight-through cable.
db-25-female-dte: DB-25 female DTE is the standard RS-232 connector
on a computer, terminal, or printer. When looking at the connector, the pin numbers are: 13 12 11 10 9 8 7 6 5 4 3 2 1 25 24 23 22 21 20 19 18 17 16 15 14
Here are the most common pins:
| pin | signal | signal direction from computer's point of view |
| 2 | TxD | out |
| 3 | RxD | in |
| 4 | RTS | out |
| 5 | CTS | in |
| 6 | DSR | in |
| 7 | GND | - |
| 8 | DCD | in |
| 20 | DTR | out |
dce: DCE Data Communications Equipment, the RS-232 concept for
equipment (like modems) that forwards data but doesn't generate data of its own. The ethernet equivalent is 568A. See also DCE vs. DTE.
dce-vs-dte: DCE vs. DTE is the main reason we need so many
different types of cables. It is an RS-232 concept that unfortunately was inherited by the ethernet cabling standards.
The original idea behind DCE and DTE was that there were two types of equipment — "terminal" type of equipment that generates and/or receives data of its own, and "communication" type equipment that only relays data generated by someone else. Computers, printers, and teletypes and glass TTYs were all of the first type (DTE) and modems were of the other type (DCE). Then for various reasons that are now fairly insignificant they decided that the 25-pin RS-232 connectors on these two types of equipment actually needed to be wired differently, with the result being that you then needed two different types of cables: one for connecting a DTE to a DCE and another for connecting two DTE's directly to each other.
de-9-male: DE-9 male connector on PC's (originally the IBM PC-AT)
serial ports. It is a male DB-9 style connector. When looking at the back of your computer, the pin numbers are:
1 2 3 4 5 6 7 8 9
and the signal assignments are:
| pin | signal | signal direction from computer's point of view |
| 1 | DCD | in |
| 2 | RxD | in |
| 3 | TxD | out |
| 4 | DTR | out |
| 5 | GND | - |
| 6 | DSR | in |
| 7 | RTS | out |
| 8 | CTS | in |
| 9 | RI | in |
dte: DTE Data Terminal Equipment, the RS-232 concept for any
equipment that generates and/or reads data and does something with it, which means pretty nearly any type of equipment except a modem. The ethernet equivalent is 568B. See also DCE vs. DTE.
drop-cable: drop cable goes from wall plate to computer. See also
patch cable.
EIA: EIA Electronics Industry Association. See standard 568.
flex: flex or braided wire is used for drop cables
and patch cables.
level-v: Level V see Category 5.
non-plenum-grade: non-plenum grade see
plenum grade.
null-modem: null-modem cable connects the TxD (transmit data) on
one end with the RxD (receive data) on the other end. You'd think this is the only type of cable you need, but because of DCE vs. DTE you actually need two. A null-modem cable connects two DTEs to each other.
There are three common types of null-modem cables. The simplest is the three-wire cable, used when neither side expects hardware handshaking: one end other end (DTE) (DTE) TxD ------------ RxD RxD ------------ TxD GND ------------ GND
The second type is used when one end expects hardware handshaking but the other end cannot provide it. It "fakes" the hardware handshaking signals, allowing communication to happen but losing the benefit of hardware handshaking: one end other end (DTE) (DTE) TxD ------------ RxD RxD ------------ TxD RTS -. .- CTS | | CTS -' `- RTS DCD -. .- DTR | | DTR -' `- DCD GND ------------ GND
The third type is a full handshake cable, and is used when both ends are doing hardware handshaking: one end other end (DTE) (DTE) TxD ------------ RxD RxD ------------ TxD RTS ------------ CTS CTS ------------ RTS DCD -+---------- DTR DSR -' ,- DSR DTR ----------+- DCD GND ------------ GND
rxd: RxD Receive data. An input signal on a DTE and an output
signal on a DTE. See RxD vs. TxD and DCE vs. DTE.
rxd-vs-txd: RxD vs. TxD. Based on the names, you would think that
the RxD (receive data) pin is for "reading" or "watching" a voltage and that TxD (transmit data) is a pin that is producing a voltage. In fact, that is only true for DTE connectors. DCE connectors use the signal names to mean the opposite thing. This is because if the DCE vs. DTE concept which originated with the idea that a modem is fundamentally different from a terminal or computer.
patch-cable: A patch cable goes from patch panel to hub. See also
drop cable.
plenum-grade: plenum grade and non-plenum grade refer to the
outer coating of the cable and has to do with fire codes. "plenum grade" or "plenum rated" cable has a fireproof chemical coating. They will burn (anything will burn given enough temperature and oxidizer), but not as easily as non-plenum grade cable.
plenum-rated: plenum rated see plenum grade.
RJ: RJ Registered Jack (old Bell Labs acroynm)
rj-45-cable: RJ-45 cable has two male
RJ-45 connectors and up to 8 wires connecting the two ends. There are a whole lot of different types of RJ-45 cables:
A data or straight-through RJ-45 cable just connects same numbered pins to each other: 1 to 1, 2 to 2, 3 to 3, and so on. The ethernet straight-through cable would be the same if it has all 8 wires, but the twisting of the wires in pairs sometimes interferes with use as (for example) an RS-232 cable. If a data cable is wired with common 8-conductor twisted-pair ethernet wire, 4 sets of pins will be twisted, and this will cause signal cross-talk that might be a problem.
A telco RJ-45 cable is wired like a standard phone wire, connecting the pins in a mirror-image arrangement: 1 to 8, 2 to 7, 3 to 6, etc. The 8 wires are treated as four pairs (1-8, 2-7, 3-6 and 4-5). Each pair carries an AC signal on a current loop, which means that any pair can be a twisted pair without worrying about crosstalk, and the two wires within a pair can be interchanged with no noticable effect. For this reason, a straight-through RJ-45 cable can be used in a telco application.
EIA/TIA 568 cables are of two types, crossover and straight-through, described under their own entries. They treat the 8 pins as 4 pairs but the pairs are different from telco: 1-2, 3-6, 4-5 and 7-8. The pairs are always wired with twisted pair wires, and used for high-frequency signals (like 100-MBps ethernet) where crosstalk is an important concern. Therefore only 4 signals can be sent (and usually only two); one signal through each pair.
rj-45-conn: RJ-45 connector The 8-pin connector used on ethernet cables,
which looks like a modular phone cord connector but with more pins. These diagrams show the pin numbering. The female connector is shown the way it looks when you look at the socket on the back of your computer, and the male connector is shown the way it looks when you look at the end of a cable. When actually wiring a cable or socket, you might be looking at the connector the other way (from the direction the wires go into it) and in that case you'd have to compensate by reversing the order yourself. 1 2 3 4 5 6 7 8 8 7 6 5 4 3 2 1 .-:-:-:-:-:-:-:-:-. .-:-:-:-:-:-:-:-:-. | | | | | female (such as | | male (cable) | | ethernet card | | | | or hub) | | | `------. .------' `------. .------' |_ _| |_ _| - -
ScTP: ScTP is Screened Twisted-Pair cable. It has the same 4
pairs of wires as UTP, with a single piece of shielding (metal film or braid) surrounding the entire group of 8 wires.
solid: solid wire is used to run through walls. See also
flex.
SSTP: SSTP Is fully-shielded twisted-pair cable. It has the same 4 pairs
of wires as UTP, with a piece of shielding (metal film or braid) around each pair and a fifth piece of shielding surrounding the entire group of 8 wires.
standard-568: standard 568 is "EIA/TIA standard 568",
specifies the way the RJ-45 cables (see also drop cable, patch cable, crossover cable) are wired. There are four pairs of wires colored orange, blue, green and brown (one wire solid, the other mixed with white). It specifies two ways to wire the pins on the RJ-45 connector:
568B is the "standard" wiring; 568A is the "crossed over" wiring. The difference is an exchange of the two pairs (orange and green) that carry the ethernet signal. A crossover cable has one end connected by standard 568A and the other end connected by standard 568B. If you use the same standard on both ends you get a straight-through cable.
straight-through: A straight-through cable is the equivalent of a standard
RS-232 DTE-to-DCE cable, a cable that connects two pieces of equipment whose connectors are of the opposite type (transmit and receive signals in different places). See DCE vs. DTE and crossover cable.
A straight-through patch cable is wired like this:
| 568A End | 568A End |
| 1 green on white | 1 green on white |
| 2 green | 2 green |
| 3 orange on white | 3 orange on white |
| 4 blue | 4 blue |
| 5 blue on white | 5 blue on white |
| 6 orange | 6 orange |
| 7 brown on white | 7 brown on white |
| 8 brown | 8 brown |
tia: TIA Telecommunications Industry Association. See #standard
568#.
txd: TxD Transmit data. An output signal on a DTE and an input signal
on a DTE. See RxD vs. TxD and DCE vs. DTE.
utp:
UTP: UTP (Unshielded Twisted Pair) refers to pairs of wires without an
electrical shield of the type used to prevent cross-talk between pairs and/or radio interference.
Sources: Each of these web sites helped me create this page (but not one of them has all the info):
http://www.netspec.com/helpdesk/wiredoc.html
http://www.shoshin.co.jp/computer/cd/pins.html
Following are some other little bits of info that I wanted to publish but don't fit well into the rest of this page
cable bearing the words "belkin digital plumbing - pro series - optimum data transfer", "F3X171-10" is a "universal LapLink data transfer" cable. It connects from one PC's serial port to another PC's serial port, and acts like a "null modem" cable — TXD at one end is wired to RXD on the other end. In addition, there are two connectors on each end to support either type of serial connector (DB9 or DB25) and so the cable can (in theory) be modified for monitoring a serial conversation with the help of one or more additional PCs. In order to do that, you'd have to disable some of the connections on one or more of the connectors, depending on what you're trying to do. For example, if you're monitoring a communication between two computers ("A" and "B") that are connected via the DB-9 connectors, then you'd connect the DB-25 connectors to additional computers ("C" and "D") to do the monitoring. On the DB-25 connections, the TxD connections (pin 2) has to be disconnected, otherwise the TxD signals from computers C and D would interfere with the TxD signals from computers A and B.
This page was written in the "embarrassingly readable" markup language RHTF, and was last updated on 2013 Oct 14.
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