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Yost serial device wiring: RS232 on RJ45

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Yost serial device wiring
• • • • • Introduction in the Yost wiring standard Goals of the Yost serial wiring standard The Yost cable Yost RS232 to RJ45 DTE adapter wiring Yost RS232 to RJ45 DCE adapter wiring

Introduction in the Yost wiring standard
The wiring of RS232 has always been a problem. Originally the standard was definedfor DTE, data terminal equipment to DCE, data communication equipment connection, but soon people started to use the communication interface to connect two DTEs directly using null modem cables. No standard was defined for null modem connections with RS232 and not long after their introduction, several different wiring schemes became common. With DECConnect, Digital Equipment Corporation tried todefine their own standard for serial interconnection of computer devices with MMJ modified modular jack connectors. This interfacing standard became available on most of their hardware, but it wasn't adopted by other computer manufacturers. Maybe because DEC used an non-standard version of the modular jack. UTP and FTP cables with RJ45 connectors became the de-facto standard in office cablingsystems, and people started looking for ways to transmit RS232 signals over this cabling system. The RS-232D standard (more properly called EIA/TIA 561) was the official attempt for a standard to transmit RS232 over RJ45. Unfortunately this attempt didn't twist the cable internally. Therefore it primarily remained a standard for DTE to DCE connection in a world where the primary use of RS232 was tointerconnect DTEs directly. Very interesting is the RS232 to RJ45 wiring standard proposed by Dave Yost in 1987, based on earlier wiring schemes used at Berkeley University. He tried to define a standard comparable to DECConnect, where both DTEs and DCEs could be connected with one cable type. This standard was published in the Unix System Administration Handbook in 1994, and has since that momentbeen a wiring standard for many organisations. We will discuss this standard in detail here.

Goals of the Yost device wiring standard
The mess with RS232 wiring is widely known. It was the reason for starting this website. Dave Yost wanted to solve that mess once and for all, reaching as much as possible of the following goals: 1. 2. 3. 4. 5. All cable connectors should have the same connectortype (RJ45) All cable connectors should have the same connector gender (male) DTEs and DCEs should have the same connector wiring All cables should be identical (except for length) No need for null modems or other special cables for specific situations

These goals are very close to the goals DEC wanted to achieve with DECConnect. The Yost standard has however one basic advantage. Because RJ45connectors are used, eight pins are available which makes it possible to transfer almost all RS232 signals. Therefore the Yost standard can be used with much more equipment than DECConnect.

http://www.lammertbies.nl/comm/cable/yost-serial-rj45.html

8/23/2011

Yost serial device wiring: RS232 on RJ45

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The Yost cable
One cable for all solutions is the basis of the Yoststandard. This cable is not a straight through patch cable with two RJ45 connectors crimped to each end, but a cross-cable where pin 1 is connected to pin 8, pin 2 to 7 etc. The basic layout of this cable is shown below. In this picture flat cable is used, which is specially designed for use with RJ45 connectors. Do not use cross cables that are sold in some computer stores. Those cables cross somepairs to make the connection of two computers with ethernet network cards possible without a hub, but these cables are not recommended for Yost systems.
Basic Yost cable with two RJ45 connectors cross connected

RJ45 plug 1 1 2 3 4 5 6 7 8

RJ45 plug 2 8 7 6 5 4 3 2 1

Function CTS CD Rx RTS DTR Tx

Signal ground Signal ground Tx DTR RTS Rx CD CTS

I have used the DTE signal names here,...