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PC Wiring Pin Out / Diagrams



Network Wiring Pin Out

Referenced from

T-568 and Telephone Color Codes

Telephone Cable


RJ-11 Plug Wiring

This is the wiring for the plug side of an RJ-11 connector. Can you say "BRGY"? (Think about cheap red wine; I know I do.) The diagram is shown with the "hook" - the little thing you press on to get the plug out - underneath. RJ-11 sockets always have the colors indicated on the terminals.

 Note that the connector on the other end of an RJ-11 connector is wired in reverse order. That is, if you stretch the cable out flat, the Black wire stays on the left all the way to the other end, including through the connector with the hook oriented down also. Also note that the RJ-11 connector has six terminals on it. Only the middle 4 are normally used. Line 1 is the center pair: red and green, as in Christmas.

T-568B Color Code for RJ-45 Plug

Eight-conductor data cable contains 4 pairs of wires. Each pair consists of a solid (or predominantly) colored wire and a white wire with a stripe of the same color. The pairs are twisted together. To maintain reliability on Ethernet, you should not untwist them any more than necessary (like about 1 cm).

There are two wiring standards for these cables, called "T-568A" and T-568B" They differ only in connection sequence, not in use of the various colors. The illustration shown is for T-568B. The pairs designated for 10BaseT Ethernet are Orange and Green. The other two pairs, Brown and Blue, can be used for a second Ethernet line or for phone connections.

 Note that the Blue pair is on the center pins and conveniently corresponds to the Red and Green pair in a normal phone line. The connections shown are specifically for an RJ45 plug (the thing on the end of the wire). The wall jack may be wired in a different sequence because the wires are actually crossed inside the jack. The jack should either come with a wiring diagram or at least designate pin numbers that you can match up to the color code below.

Pin Number Designations
There are pin number designations for each color in T568B as well. The pin designations are as follows:

   Color Codes for T568B
Pin     color  pair  name
---     -----  ---- ---------
1       wh/or   2   TxData +
2       or      2   TxData -
3       wh/grn  3   RecvData+
4       blu     1
5       wh/blu  1
6       grn     3   RecvData-
7       wh/brn  4
8       brn     4

Note that the odd pin numbers are always the white with stripe color.

Info found at

Wiring Diagrams for Straight Through, Cross Over and Y cables

Note: The hook is underneath in all cases and Pin one is always on the Left


Straight Through Cable Color Code Color
Pin 1 
Pin 2
Pin 3
Pin 4
Pin 5
Pin 6
Pin 7
Pin 8
white orange
white green
white blue
white brown


Cross Over Cable Color Code Color
Pin 1 
Pin 2
Pin 3
Pin 4
Pin 5
Pin 6
Pin 7
Pin 8
white green
white orange
white blue
white brown

The other side is a straight through cable see Straight through diagram


Y Cable Color Code Color
Pin 1 
Pin 2
Pin 3
Pin 6

Pin 1
Pin 2
Pin 3
Pin 6

white orange
white green

white blue
white brown

The other side is a straight through cable see Straight through diagram


Straight-Through vs Cross-Over

In general, the patch cords that you use with your Ethernet connections are "straight-through", which means that pin 1 of the plug on one end is connected to pin 1 of the plug on the other end (for either standard). The only time you cross connections in 10BaseT is when you connect two Ethernet devices directly together without a hub or connect two hubs together. Then you need a "cross-over" patch cable, which crosses the transmit and receive pairs. An easy way remember how to make a cross-over cable is to wire one end with the T-568A standard and the other with the T-568B standard.



UTP cables are terminated with standard connectors, jacks and punchdowns. The jack/plug is often referred to as a "RJ-45", but that's a  telco designation for the "modular 8 pin connector" terminated with a USOC pinout used for telephones. The male connector on the end of a patchcord is called a "plug" and the receptacle on the wall outlet is a "jack."

In LANs, as spec'ed by 568, there are two possible pinouts, called T568A and T568B, that differ only in which color coded pairs are connected - pair 2 and 3 are reversed. Either work equally well, as long as you don't mix them! If you always use only one version, you're OK, but if you mix A and B in a cable run, you will get crossed pairs!

The cable pairs are color coded as

Pair 1 is white-blue/blue,
Pair 2 white-orange/orange,
Pair 3 is white-green/green
Pair 4 is white-brown/brown.




RS232 Connections, and wiring up serial devices

Referenced from

--AirBorn Electronics--


RS232 Pin Assignments (DB25 PC signal set)
Pin 1 Protective Ground
Pin 2 Transmit Data
Pin 3 Received Data
Pin 4 Request To Send
Pin 5 Clear To Send
Pin 6 Data Set Ready
Pin 7 Signal Ground
Pin 8 Received Line Signal Detector
(Data Carrier Detect)
Pin 20 Data Terminal Ready
Pin 22 Ring Indicator

The connector on the PC has male pins, therefore the mating
cable needs to terminate in a DB25/F (Female pin) connector.

RS232 Pin Assignments (DB9 PC signal set)
Pin 1 Received Line Signal Detector
(Data Carrier Detect)
Pin 2 Received Data
Pin 3 Transmit Data
Pin 4 Data Terminal Ready
Pin 5 Signal Ground
Pin 6 Data Set Ready
Pin 7 Request To Send
Pin 8 Clear To Send
Pin 9 Ring Indicator

The connector on the PC has male pins, therefore the mating
cable needs to terminate in a DB9/F (Female pin) connector.

Wiring up something nice and simple, for instance a plain old "dumb terminal", is just a matter of connecting Tx, Rx and Ground, right?

Usually Not. While the normal PC hardware might well run with just Tx, Rx and Ground connected, most driver software will wait forever for one of the handshaking lines to go to the correct level. Depending on the signal state it might sometimes work, other times it might not. The reliable solution is to loop back the handshake lines if they are not used.

Handshake looping a PC serial connector

When the lines are handshake looped, the RTS output from the PC immediately activates the CTS input - so the PC effectively controls its own handshaking.

RS232 DB9 PC Loopback test plug

The PC loopback plug is a useful diagnostic tool. The loopback plug connects serial inputs to serial outputs so that the port may be tested. There is more than one way to wire up a loopback plug - but this is the most common.

RS232 DB25 PC Loopback test plug

Connecting together two serial devices involves connecting the Rx of one device to the Tx of the other, and vice versa. The diagram below indicates how you would go about connecting two PC's together, without handshaking.

Connecting two PCs together using RS232, without handshaking

When Handshaking is required, generally RTS of one device connects to CTS of the other, and vice versa, and also DSR of one device connects to DTR of the other device, and vice versa. The particular requirements for different equipment may vary.

Connecting two PCs together using RS232, with handshaking

Using a Breakout box or LED box to work out cabling

If you have problem with RS232 cabling, your best "emergency" tool may be a breakout box (sometimes called an LED box). Generally these units only come in the DB25 size, but with a couple of DB9 to DB25 adaptors, they can be used with DB9 cables as well. The units have an LED for each signal line in the cable, and the LED lights green or red dependent on the signal state. The Breakout box also allows you to disconnect certain lines in the cable, and patch in new ones - good for trying new cable wiring possibilities.

The first thing to remember, is that there is a good chance the two devices you are trying together will actually work if you can get the cable correct. If you have some other way to actually prove this - for instance by trying each of the devices on another system - do it.

Given a hypothetical example - for instance connecting a standard PC with a DB25M to a 200 disk CD changer with a DB25M, the first thing I would try and do is get a cable that I think would work. In this instance, I would either purchase or build a null-modem cable (DB25F to DB25F) - similar to the last example, basically the cable used to connect two PCs together with handshaking, only DB25F to DB25F instead of DB9F to DB9F.

Given the cable that I believe will work, connect the cable, LED box and two devices all together. Before powering on both devices, unplug just one of them. Power the devices on and make a note of which LEDs are lit. Then unplug the connected device and plug in the disconnected one, without rearranging the cabling otherwise. Again make a note of which LEDs are lit. If any single LED is lit by both of the devices, then there is an output conflict, and the cable wiring is incorrect. By this, I mean that one line in the cable has an output driving it from both ends - and this is not correct for RS232 - so that means that the cable wiring is not correct for the devices. Pay particular attention to Tx and Rx.

To continue with the example above, if I saw that two ends were driving the same lines, I would assume the null modem cable was not correct, and I would try a one-for-one gender changer instead.

If each end drives its own set of LEDs, connect the two ends together. In normal situations, you should see all the LEDs light up - but there are some devices which will not light up all the LEDs. Having said that, if one of the devices is a PC and any LED except RI (Ring indicator) is not lit up, the cable will probably not work.

Normally, other cabling problems will involve handshake lines. An LED box will be an invaluable guide, but there is no trivial test to determine the solution. An LED Box will also show the lines as they change state, although it is usually quite hard to see the serial communications themselves unless the comms are continuous, or at a low baud rate (9600 baud or lower is usually visible).

Using a 'T' plug and a PC to monitor comms

The gadget below is a quick 10 minute project that is really great for monitoring RS232 Comms using a PC.

A gadget for monitoring RS232 Comms between two devices

There are three sockets on our monitoring gadget. Two of them are connected straight through - you plug them in series with the devices you wish to monitor - and the third goes off to another monitoring PC.

The monitoring PC "Sees" on its serial port both sides of the serial conversation - that is it sees what is sent by PC1 and also what is sent by PC2. This can be a positive advantage, because you can see the serial conversation as it progresses between the two devices. Some serial protocols, however, talk "full duplex" meaning that one end can start transmitting while it is still receiving from the other end. This unit cannot monitor full duplex Comms - you will see gobble-dee-gook where the two transmissions overlap.

If you try this unit, you will be surprised how useful it is, and how often it works - mostly because many supposedly full duplex installations still talk half duplex in any case, because that is the sensible way to write the software. Not bad for one diode and a resistor, huh?

For information on other types of connectors, check out:
or for PC HW:






Serial and Parallel cable schematics and wiring diagrams.

Referenced from

Use the I/O ActiveX control for serial and parallel communication.  ASCII Code Table

9 PIN to 9 PIN Serial Cable

25 PIN to 9 PIN Serial Cable

Parallel Printer Connector Db-25
DB-25 PIN (Female) SIGNAL
1 ------------------------------- > STROBE *
2 ------------------------------- > DATA 0
3 ------------------------------- > DATA 1
4 ------------------------------- > DATA 2
5 ------------------------------- > DATA 3
6 ------------------------------- > DATA 4
7 ------------------------------- > DATA 5
8 ------------------------------- > DATA 6
9 ------------------------------- > DATA 7
10< ------------------------------ ACK *
11< ------------------------------ BUSY
12< ------------------------------ PAPER END
13 ------------------------------ SLCT (select)
14 ------------------------------ >AUTOFEED *
15< ------------------------------ ERROR *
16 --------------------------->INITIALIZE PRINTER *
17 ------------------------------- SLCTIN (select in)
18 thru 25 ----------------------- GND
Note!! * denotes an active low signal.
Db-25 Parallel Loopback Connector Wiring
1 to 13 Strobe to select
10 to 16 ACK to INIT
11 to 17 BUSY to SLCTIN
12 to 20 PAPER END to GND


Rs-232 Serial (Com) Pc Port Connector Db-9
1 --------------------------- Data Carrier Detect CD or DCD
2 ------------------------------ Receive Data RD or RX
3 ---------------------------- Transmitted Data TX or TD
4 ---------------------------- Data Terminal Ready DTR
5 ------------------------------ Signal Ground GND
6 ------------------------------ Data Set Ready DSR
7 ------------------------------ Request To Send RTS
8 ------------------------------ Clear To Send CTS
9 ------------------------------ Ring Indicator RI
Transmitted and receive data are referenced from the data device and not the modem.


Rs-232 Serial (Com) Pc Port Connector Db-25
1 ---------------------------- Chassis/Frame Ground GND
2 ------------------------------ Transmitted Data TX or TD
3 -------------------------------- Receive Data RX or RD
4 ------------------------------ Request To Send RTS
5 ------------------------------- Clear To Send CTS
6 ------------------------------- Data Set Ready DSR
7 ------------------------------- Signal Ground GND
8 ---------------------------- Data Carrier Detect DCD or CD
9 ------------------------- Transmit + (Current loop) TD+
11 ------------------------ Transmit - (Current Loop) TD-
18 ------------------------- Receive + (Current Loop) RD+
20 --------------------------- Data Terminal Ready DTR
22 ----------------------------- Ring Indicator RI
25 ------------------------- Receive - (Current Loop) RD-
NOTE!! Current loop technology was supported in the PC and XT interfaces.
Current loop was discontinued when the AT interface was introduced. Transmitted and receive data are referenced from the data device and not the modem.


Db-25 Female Serial Loopback Plug Wiring
2 to 3 Xmit to Rec data
4 to 5 to 22 RTS to CTS to RI
6 to 8 to 20 DSR to CD to DTR
Db-9 Female Serial Loopback Plug Wiring
2 to 3 Xmit to Rec data
7 to 8 to 9 RTS to CTS to RI
6 to 1 to 4 DSR to CD to DTR
Rs-232 Serial Db-9 To Rs-232 Db-25 Adaptor
DB-9 PIN (Female) DB-25 PIN (Male)
1 ------------------------------------- 8 DCD
2 ------------------------------------- 3 TXD
3 ------------------------------------- 2 RXD
4 ------------------------------------- 20 DTR
5 ------------------------------------- 7 GND
6 ------------------------------------- 6 DSR
7 ------------------------------------- 4 RTS
8 ------------------------------------- 5 CTS
9 ------------------------------------- 22 RI
Use this pin out to adapt between the two serial connector types.


Rs-232 Serial Db-25 To Db-25 Null Modem Cable
DB-25 PIN (Female) PC DB-25 PIN (Female) PC
2 ------------------------------------- 3
3 ------------------------------------- 2
7 ------------------------------------- 7
4 ------------------------------------- 5
5 ------------------------------------- 4
6 ------------------------------------- 20
20 ------------------------------------ 6
Note!! All other pins are unused. Use this cable pinout for direct connection between two IBM compatible computers.


Rs-232 Serial Db-25 To Serial Printer Null Modem Cable
DB-9 Female PC DB-25 PIN Female PC DB-25 PIN Male printer
2 < RD --------- 3 <------------------------------------- 2 Transmitted data
3 > TD --------->2 -------------------------------------> 3 Receive data
5 < GND -------- 7 <------------------------------------> 7 Ground
8 < CTS -------- 5 ------------------------------------ 6 to 8 to 20
1 to 4 to 6 6 to 8 to 20 4 to 5
Note!! Use this cable pinout for direct connection between a PC serial port and a serial printer. The 1/4/6 and 6/8/20 loopbacks are to enable the interface as if a modem was attached.


Standard Centronics Parallel Cable Db-25 To Centronics 36
DB-25 PIN Male (PC) Centronics 36 Male
1 --------------------------------------> 1 Strobe *
2 <-------------------------------------> 2 Data bit 0 +
3 <-------------------------------------> 3 Data bit 1 +
4 <-------------------------------------> 4 Data bit 2 +
5 <-------------------------------------> 6 Data bit 3 +
6 <-------------------------------------> 6 Data bit 4+
7 <-------------------------------------> 7 Data bit 5 +
8 <-------------------------------------> 8 Data bit 6 +
9 <-------------------------------------> 9 Data bit 7 +
10 <------------------------------------- 10 Acknowledge *
11 <------------------------------------- 11 Busy +
12 <------------------------------------- 12 Paper out +
13 <------------------------------------- 13 Select (in) *
14 -------------------------------------> 14 Auto Feed *
15 <------------------------------------- 32 Error *
16 -------------------------------------> 31 Initialize printer *
17 -------------------------------------> 36 Select (out) *
18 thru 25 Gnd 16, 19 thru 30, 33 Ground 15, 17, 18, 34, 35 No connection
Note!! * denotes and active low signal. This pin out depicts the newer bi-directional parallel port with input and output capabilities often used with external tape drives and accessory devices. If pins 31 or 32 are grounded on a cable the printer will fail to come ready when attached to the PC. This is common on low cost parallel printer cables.








Referenced from


S-Video is a technical specification for the transfer of video information via a 4 pin mini din cable.  These leads are sometimes also referred to as 'S-VHS' leads, which is technically incorrect.  However, the two names can be used interchangeably to refer to the same type of cable. These leads are commonly used for connecting video sources such as video cameras, PC Video Grabber cards, DVD players etc., to other devices and of course to televisions.

Contrary to popular belief this type of lead carries video signals ONLY, and no audio whatsoever. The connections for s-video wiring are as displayed below:

Diagram of the soldered side of an S-Video connector

Front view diagram of an S-Video connector





Paul J Reitschky











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