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| '''RS-232 Cabling''' | | '''RS-232 Cabling''' |
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| RS-232: The basics | | RS-232 Name/Function DB-25 DB-9 RJ-45 RJ-45 |
| | | Signal (Input/Output) (Standard) (Standard) (Cyclades) (Netra/Cisco) |
| RS-232C, EIA RS-232, or simply RS-232, refers to the same standard defined by the Electronic Industries Association in 1969 for serial communication.
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| More than 30 year later, we have found more applications for this standard than its creators could ever imagine. Almost any electronic device nowadays has serial communication ports.
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| RS-232 was defined to connect a DTE (Data Terminal Equipment, usually a computer or terminal) to a DCE (Data Communication Equipment, usually a modem):
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| DTE -- RS-232 -- DCE -- communication line -- DCE -- RS-232 -- DTE
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| Nowadays, RS-232 is mostly being used to connect DTE devices directly (without modems or communication lines). While that was not the original intention, it is possible with some wiring tricks
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| The relevant signals (or wires) in a RS-232 cable, from the computer (DTE) standpoint, are:
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| Receive Data (RxD) and Transmit Data (TxD) -- The actual data signals
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| Signal Ground (Gnd) -- Electrical reference between the two ends
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| Data Terminal Ready (DTR) -- Indicates that the computer (DTE) is active
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| Data Set Ready (DSR) --Indicates that the modem (DCE) is active.
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| Data Carrier Ready (DCD) -- Indicates that connection over the communication line is active
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| CTS (Clear to Send, an input) -- Flow control for data flowing from DTE to DCE
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| RTS (Request to Send, an output) -- Flow control for data flowing from DCE to DTE
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| Not all signals are necessary in every application. So, the RS-232 cable may have less than 7 wires.
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| The RS-232 interface defines communication parameters such as parity, number of bits per character, number of stop-bits and the baud-rate. For communication to happen, both sides should be configured with the same parameters. That is the first thing to verify if you think you have the right cable and things still don’t work. The most common configuration is 8N1 (8 bits of data per character, no parity bit included with the data, 1 stop-bit to indicate the end of a character).
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| The "baud rate" in a RS-232 line translates directly into the data speed in bits per second (BPS). Usual transmission speeds range from to 9600 and 19200 BPS (used in most automation and console applications) to 115200 BPS (used by the fastest modems).
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| Cable: How long, how good?
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| The original RS-232 specifications were defined to work at a maximum speed of 19200 BPS over distances up to 15 meters (or about 50 feet). That was 30 years ago. Today, RS-232 interfaces can drive signals through longer cables and faster.
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| As a general rule, consider:
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| If the speed is lower than 38.4 KBPS, you are safe with any cable up to 30 meters (100 feet)
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| If the speed is 38.4 BPS or higher, keep cables shorter than 10 meters (30ft)
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| If your application is outside the above limits (high speed, long distances), you will need better quality (low-impedance, low-capacitance) cables.
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| Successful RS-232 data transmission depends on many variables that are specific to each environment. The general rules above are empirical and have a lot of safety margins built-in.
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| Connectors, connectors
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| The connector traditionally used with RS-232 is the 25-pin D-shaped connector (DB-25). Most analog modems and most of the older computers and serial equipment use this connector. RS-232 interface on DB-25 always uses the same standard pin assignment.
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| The 9-pin D-shaped connector (DB-9) saves some space and is also used for RS-232. Most new PC COM ports and serial equipment (specially the ones where compact size is important) uses this connector. RS-232 interfaces on DB-9 always use the same standard pin assignment.
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| The telephone-type modular RJ-45 plug and jack are very compact, inexpensive and compatible with the phone and Ethernet wiring systems present in most buildings and data centers. Most of the networking equipment and newest servers use RJ-45 connectors for serial communication. Unfortunately there is no standard for RS-232 pin assignment on RJ-45 connectors. Every equipment vendor has its pin assignments.
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| Most connectors have two versions. The ones with pins are said to be "male" and the ones with holes said to be "female".
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| RS-232
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| Signal Name/Function | |
| (Input/Output) | |
| DB-25 pins
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| (Standard) | |
| DB-9 pins
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| (Standard) | |
| RJ-45 pins
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| (Cyclades) | |
| RJ-45 pins
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| (Netra/Cisco) | |
| Chassis Safety Ground
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| 1
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| Shell
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| Shell
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| Shell
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| Gnd Signal Ground
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| 7
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| 5
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| 4
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| 4
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| TxD Transmit Data (O)
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| 2
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| 3
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| 3
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| 3
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| RxD Receive Data (I)
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| 3
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| 2
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| 6
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| 6
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| DTR Data Terminal Ready (O)
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| 20
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| 4
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| 2
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| 2
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| DSR Data Set Ready (I)
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| 6
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| 6
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| 8
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| 7
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| DCD Data Carrier Detect (I)
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| 8
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| 1
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| 7
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| -
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| RTS Request To Send (O)
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| 4
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| 7
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| 1
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| 1
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| CTS Clear To Send (I)
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| 5
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| 8
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| 5
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| 8
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| Straight Through or Crossover?
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| The RS-232 interface was originally intended to connect a DTE (computer, printer and other serial devices) to a DCE (modem) using a straigh-though cable (all signals in one side connected to the corresponding signals in the other side in a one-to-one basis).
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| By using some "cabling tricks", we can use RS-232 to connect two DTEs and this is the case in most of the modern applications.
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| A crossover (a.k.a. null-modem) cable is used to connect two DTEs directly, without modems or communication lines in between. They cross transmit and receive data signals between the two sides and there are many variations on how the other control signals are wired.
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| A "complete" crossover cable would connect the TxD with RxD, DTR with DCD/DSR, and RTS with CTS across both sides. A "simplified" crossover cable would cross TxD and RxD and locally short-circuit DTR with DCD/DSR and RTS with CTS.
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| Cables or adapters?
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| Besides cables, it is possible to use a set of a cable plus an adapter to connect two equipments. At first it may sound a little strange to replace a single cable with two devices, but in some cases it may be an interesting solution. An adapter is a Òsmall boxÓ with connectors on two of its sides. The connectors have exactly the same pinout of a cable. Most data centers already have standard cables, like CAT5 Ethernet cables (RJ-45 to RJ-45, straight through), promptly available. Instead of buying new non-standard cables, it is much easier to buy adapters and use the existing cables. Adapters may also help companies with special requirements in terms of cable length and color. The possible increase in cost and in the lead time of a cable with these features could be avoided with the use of adapters.
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| What Cable Should I Use?
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| First, look up the right cable for your application in the tables below. After that, purchase the standard pre-made cables from a computer store or cable vendor. For custom cables, refer to the cable diagrams to build your own cables or order them from Cyclades or a cable vendor.
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| If your Cyclades product presents the RS-232 interface on a DB-25 connector, refer to table 1. If your Cyclades product presents the RS-232 interface on a RJ-45 jack, refer to table 2.
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| To Connect Cyclades To Use Cable
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| DB-25 Male Standard
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| Cyclom-Yo
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| Cyclom-Ye/DB-25
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| Cyclades-8Zo
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| DCE DB-25 Female (standard)
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| - Analog Modems
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| - ISDN Terminal Adapters
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| 1 - DB-25 F to DB-25 M straight-through (standard)
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| This cable is standard and can be purchased pre-made at computer stores
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| DTE DB-25 Male or Female (standard)
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| - Serial Terminals
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| - Old PC COM ports
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| - Most Serial Printers
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| - Some Console Ports
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| - Most automation devices
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| 2 - DB-25 F to DB-25 F/M crossover (standard)
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| This cable can be purchased pre-made at computer stores (exact wiring may vary).
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| DTE DB-9 Male or Female
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| - Newer PC COM ports
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| - Most Mice and pointing devices
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| - Some automation devices
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| 3 - DB-25 F to DB-9 F/M crossover (standard)
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| This cable is standard, but it may be difficult to find it pre-made. You may combine a DB-25 crossover cable with a DB-25 to DB-9 converter.
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| Table 1
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| To Connect Cyclades To Use Cable
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| RJ-45Cyclades Custom
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| Cyclom-Ye/RJ-45
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| Cyclades-Ze
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| TS Series
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| AlterPath™ ACS
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| AlterPath™ SM100
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| DCE DB-25 Female (standard)
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| - Analog Modems
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| - ISDN Terminal Adapters
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| 4 -- RJ-45 to DB-25 M straight-through (Custom)
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| This custom cable can be ordered from Cyclades (a 6ft cable RJ-45 to DB-25 male is available - ask for the part number CAB0025) or other cable vendors. A sample is included with the products ("straight-through").
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| DTE DB-25 Male or Female (standard)
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| - Serial Terminals
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| - Old PC COM ports
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| - Most serial printers
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| - Some Console Ports
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| - Most automation devices
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| 5 -- RJ-45 to DB-25 F/M crossover (Custom)
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| This custom cable can be ordered from Cyclades (a 6ft RJ-45 to DB-25 female cable is available - ask for the part number CAB0017) or other cable vendors. A sample is included with the products ("Console").
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| One adapter RJ-45 to DB-25 female (part number ADB0025) and one adapter RJ-45 to DB-25 female (part number ADB0017) are included with the TS series, with the AlterPath™ ACS and with the AlterPath™ SM100.
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| DTE DB-9 Male or Female (standard)
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| - Newer PC COM ports
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| - Most Mice and pointing devices
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| - Some automation devices
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| 6 -- RJ-45 to DB-9 F/M crossover (Custom)
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| This custom cable can be ordered from Cyclades (a 6ft RJ-45 to DB-9 female cable is available - ask for the part number CAB0036) or other cable vendors. A sample is included with the products ("Console").
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| One adapter RJ-45 to DB-9 male (part number ADB0017) and one RJ-45 to DB -9 female (part number ADB0036) are included with the TS series, with the AlterPath™ ACS and with the AlterPath™ SM100.
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| DTE RJ-45 Cyclades (custom)
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| - All Cyclades Console Ports
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| 7 -- RJ-45 to RJ-45 crossover (Custom)
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| This custom cable can be ordered from cable vendors using the provided wiring diagram.
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| DTE RJ-45 Netra (custom)
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| - Sun Netra Console Ports
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| - Cisco Console Ports
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| 8- RJ-45 to RJ-45 crossover (Custom)
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| This custom cable can be ordered from Cyclades (a 10ft cable is available - ask for the part number CAB0045) or cable vendors.
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| One adapter is included with the TSseries, with the AlterPath™ ACS and with the AlterPath™ SM100.
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| Table 2
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| Cable Diagrams
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| Before using the following cable diagrams refer to the tables above to select the correct cable for your application.
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| Sometimes, crossover cables are wired slightly differently depending on the application. A "complete" crossover cable would connect the TxD with RxD, DTR with DCD/DSR, and RTS with CTS across both sides. A "simplified" crossover cable would cross TxD and RxD and locally short-circuit DTR with DCD/DSR and RTS with CTS.
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| Most of the diagrams in this document show the "complete" version of the crossover cables, with support for modem control signals and hardware flow control. Applications that do not require such features have just to configure NO hardware flow control and NO DCD detection on their side. Both ends should have the same configuration for better use of the complete version of the cables shown below.
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| Cable #1: DB-25 Female to DB-25 Male, Straight Through
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| DB-25 Female to DB-25 Male, Straight Through Application: It connects
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| Cyclades products (serial ports) to modems and other DCE RS232 devices.
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| DB-25 DB-25
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| Female Male
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| -------- --------
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| 2 TxD ------------ TxD 2
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| 3 RxD ------------ RxD 3
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| 7 Gnd ------------ Gnd 7
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| 20 DTR ------------ DTR 20
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| 6 DSR ------------ DSR 6
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| 8 DCD ------------ DCD 8
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| 4 RTS ------------ RTS 4
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| 5 CTS ------------ CTS 5
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| Cable #2: DB-25 Female to DB-25 Female/Male, Crossover
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| DB-25 Female to DB-25 Female/Male, Crossover Application: It connects Cyclades products
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| (serial ports) to console ports, terminals, printers and any other DTE RS232 device.
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| DB-25 DB-25
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| Female F/M
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| -------- --------
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| 2 TxD ------------ RxD 3
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| 3 RxD ------------ TxD 2
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| 7 Gnd ------------ Gnd 7
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| 20 DTR --------|--- DSR 6
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| |--- DCD 8
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| 6 DSR ---|-------- DTR 20
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| 8 DCD ---|
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| 4 RTS ------------ CTS 5
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| 5 CTS ------------ RTS 4
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| Cable #3: DB-25 Female to DB-9 Female, Crossover
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| DB-25 Female to DB-9 Female, Crossover Application: It connects Cyclades products (serial ports)
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| to console ports, terminals, printers and any other DTE RS232 device.
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| DB-25 DB-9
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| Female F/M
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| -------- ---------
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| 2 TxD ------------ RxD 2
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| 3 RxD ------------ TxD 3
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| 7 Gnd ------------ Gnd 5
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| 20 DTR --------|--- DCD 1
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| |--- DSR 6
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| 6 DSR ---|-------- DTR 4
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| 8 DCD ---|
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| 4 RTS ------------ CTS 8
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| 5 CTS ------------ RTS 7
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| Cable #4: Cyclades RJ-45 to DB-25 Male, Straight Through
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| Cyclades RJ-45 to DB-25 Male, Straight Through Application: It connects
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| Cyclades products (serial ports) to modems and other DCE RS232 devices.
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| RJ-45 DB-25
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| Cyclades Male
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| -------- --------
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| 3 TxD ------------ TxD 2
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| 6 RxD ------------ RxD 3
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| 4 Gnd ------------ Gnd 7
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| 2 DTR ------------ DTR 20
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| 8 DSR ------------ DSR 6
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| 7 DCD ------------ DCD 8
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| 1 RTS ------------ RTS 4
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| 5 CTS ------------ CTS 5
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| Cable #5: Cyclades RJ-45 to DB-25 Female/Male, Crossover
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| Cyclades RJ-45 to DB-25 Female/Male, Crossover Application: It connects Cyclades products
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| (serial ports) to console ports, terminals, printers and any other DTE RS232 device.
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| RJ-45 DB-25
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| Cyclades F/M
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| -------- --------
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| 3 TxD ------------ RxD 3
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| 6 RxD ------------ TxD 2
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| 4 Gnd ------------ Gnd 7
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| 2 DTR --------|--- DSR 6
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| |--- DCD 8
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| 7 DCD ---|-------- DTR 20
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| 8 DSR ---|
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| 1 RTS ------------ CTS 5
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| 5 CTS ------------ RTS 4
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| Cable #6: Cyclades RJ-45 to DB-9 Female, Crossover
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| Cyclades RJ-45 to DB-9 Female, Crossover Application: It connects Cyclades products
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| (serial ports) to console ports, terminals, printers and any other DTE RS232 device.
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| RJ-45 DB-9
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| Cyclades F/M
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| -------- --------
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| 3 TxD ------------ RxD 2
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| 6 RxD ------------ TxD 3
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| 4 Gnd ------------ Gnd 5
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| 2 DTR --------|--- DCD 1
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| |--- DSR 6
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| 7 DCD ---|-------- DTR 4
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| 8 DSR ---|
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| 1 RTS ------------ CTS 8
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| 5 CTS ------------ RTS 7
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| Cable #7: Cyclades RJ-45 to Cyclades RJ-45, Crossover
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| Cyclades RJ-45 to Cyclades RJ-45, Crossover Application: Usually used to connect
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| two ports of a Cyclades product together ("loopback") for testing purposes.
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| RJ-45 RJ-45
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| Cyclades Cyclades
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| -------- --------
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| 3 TxD ------------ RxD 6
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| 6 RxD ------------ TxD 3
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| 4 Gnd ------------ Gnd 4
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| 2 DTR --------|--- DCD 7
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| |--- DSR 8
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| 7 DCD ---|-------- DTR 2
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| 8 DSR ---|
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| 1 RTS ------------ CTS 5
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| 5 CTS ------------ RTS 1
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| Cable #8: Cyclades RJ-45 to Sun/Cisco RJ-45, Crossover
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| Usually used in console management applications to connect Cyclades
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| products to a Sun Netra server or to a Cisco product.
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| RJ-45 RJ-45
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| Cyclades Sun/Cisco
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| -------- ---------
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| 3 TxD ------------ RxD 6
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| 6 RxD ------------ TxD 3
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| 4 Gnd --------|--- Gnd 4
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| |--- Gnd 5
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| 2 DTR ------------ DSR 7
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| 7 DCD ------------ DTR 2
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| 1 RTS ------------ CTS 8
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| 5 CTS ------------ RTS 1
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| All documents on this site are property of Cyclades Corporation and may not be duplicated or republished without the written consent of Cyclades Corporation
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| ® Copyright 2007 Avocent
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Connectors
RJ45 Jack and Plug Pinout.
Cable connector's picture.
Ethernet Cabling
The TIA/EIA-568-A specifies two wiring standards for a 8-position modular connector such as RJ45. The two wiring standards, T568A and T568B vary only in the arrangement of the colored pairs. We are using T568B.
Straight-Through Cable Pinout (T568B):
RJ45 Pin # Wire Color 10Base-T Signal 1000Base-T Signal
(T568B) 100Base-TX Signal
1 White/Orange Transmit+ BI_DA+
2 Orange Transmit- BI_DA-
3 White/Green Receive+ BI_DB+
4 Blue Unused BI_DC+
5 White/Blue Unused BI_DC-
6 Green Receive- BI_DB-
7 White/Brown Unused BI_DD+
8 Brown Unused BI_DD-
Cross Over Cable Pinout (T568B):
RJ45 Pin # Wire Color RJ45 Pin # Wire Color
(END 1) (END 2)
1 White/Orange 1 White/Green
2 Orange 2 Green
3 White/Green 3 White/Orange
4 Blue 4 White/Brown
5 White/Blue 5 Brown
6 Green 6 Orange
7 White/Brown 7 Blue
8 Brown 8 White/Blue
NOTE: The cross over cable layout is suitable for 1000Base-T operation, all 4 pairs are crossed.
The following diagram shows the Normal use of Crossed and Straight cables:
straight--HUB,SWITCH--crossed--HUB,SWITCH--straight--PC
PC--crossed--PC
NOTE': To avoid the need for Crossed cables many vendors provide UPLINK ports on Hubs or Switches - these are specially designed to allow the use of a STRAIGHT cable when connecting back-to-back Hubs or Switches. Read the manufacturers documentation carefully.
RS-232 Cabling
RS-232 Name/Function DB-25 DB-9 RJ-45 RJ-45
Signal (Input/Output) (Standard) (Standard) (Cyclades) (Netra/Cisco)
