Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!grand!day From: day@grand.UUCP (Dave Yost) Newsgroups: comp.dcom.modems Subject: Partial RS-232 Solution Message-ID: <377@grand.UUCP> Date: Fri, 4-Sep-87 02:19:30 EDT Article-I.D.: grand.377 Posted: Fri Sep 4 02:19:30 1987 Date-Received: Sat, 5-Sep-87 14:37:45 EDT Organization: Grand Software, Inc., 213-650-1089, Los Angeles, CA Lines: 216 Keywords: RS-232 I thought I would hoist this up the pole in this group, seeing all the RS-232 discussion flying about. If anyone can add to the vendor information in this little piece, please let me know. Thanks. ===== Dave Yost 213-650-1089 Grand Software, Inc. {uunet,attmail}!grand!dyost or dyost@grand.COM 8464 Kirkwood Drive Los Angeles, CA 90046 Yost RS-232 RJ-45 connections September 3, 1987 Here is a scheme that solves three of the Seven Great RS-232 Hassles: 1. All cable connectors are the same sex. 2. There is no distinction between DTE and DCE. 3. You can mass-terminate connector cables. Corollary to 1 and 2: the only difference from one cable to the next is the length; there are no wiring differences. Theory of Operation Each port on every piece of equipment at your site gets its own appropriately-wired RS-232 to RJ-45 adaptor that you permanently screw onto the port connector, and everything is connected with RJ-45 cables instead of RS-232 cables. Thus, every port presents the same connector interface, RJ-45 Female, regardless of whether its underlying DB-25 connector was male or female, and cables can be made easily using an RJ-45 crimp tool. Now comes the tricky part that makes it all worthwhile: the wiring of the adpators and the cables. The RS-232 pinout scheme segregates equipment into two categories, DTE (Data Terminal Equipment, i.e. terminals) or DCE (Data Communications Equipment, i.e. modems), with the implicit and very archaic assumptions that there are only terminals and modems, and the only connections you ever need to make are from terminals to modems. Now (unfortunately) RS-232 is used by other things, like computers, which are sometimes wired as DCE and sometimes as DTE. If you want to connect DTE to DTE or DCE to DCE you have pinouts that don't match and you have to make special cables. The approach presented here erases the distinction between DTE and DCE; every piece of equipment has compatible pinouts at the RJ-45 interface. RS-232 signals can be viewed simply as 3 outputs, 3 corresponding inputs, and ground: Simplified Name DCE DTE ----------------------- ------------ Secondary Modem Control CTS----->CTS Primary Modem Control DCD----->DCD Data RxD----->RxD Ground GND------GND Data TxD<-----TxD Primary Modem Control DTR<-----DTR Secondary Modem Control RTS<-----RTS (DSR is not that important and can be ignored) Yost RS-232 RJ-45 connections September 3, 1987 page 2 The goal is to connect corresponding outputs and inputs. Rearranging the previous table slightly and doubling the ground connection, we have: Adaptor DCE DTE -------------------------------- ----- ----- Transmit Secondary Modem Control CTS--> RTS--> ----+ Transmit Primary Modem Control DCD--> DTR--> ---+| Transmit Data RxD--> TxD--> --+|| Ground GND--- GND--- -+||| |||| Ground GND--- GND--- -+||| Receive Data TxD<-- RxD<-- --+|| Receive Primary Modem Control DTR<-- DCD<-- ---+| Receive Secondary Modem Control RTS<-- CTS<-- ----+ The obvious bilateral symmetry here maps nicely to an 8-conductor RJ-45 flat cable: one side of the cable transmits in one direction, the other side in the other direction. If you don't need secondary modem control, you can crimp 6-conductor cable into the center 6 positions of the connector. If you don't need any modem control, you can crimp 4-conductor cable into the center 4 positions of the connector. To connect devices, you make your cables "with a twist" or "mirror image", or "side-to-side reversed", or whatever you want to call it, so each transmit signal goes to its corresponding receive signals at the other end. Once you have put these adaptors onto your RS-232 ports, you can simply connect anything to anything without: * Using null-modems or null-terminals * Changing pins on cable connectors * Building special cables You can connect * modem to computer * modem to terminal * terminal to computer * terminal to terminal * computer to computer etc., etc., with one kind of cable. The cables are made from jacketed, 8-conductor flat cable that is easily mass-terminated to the connectors with a crimp tool. Yost RS-232 RJ-45 connections September 3, 1987 page 3 The actual pinouts are: Cable Page DCE name DTE name Sun-MTI other --------- ---- -------- -------- ------- ----- / Gy --- Br Wh 5 CTS--> 4 RTS--> 4 ? | O --- Bl Br 8 DCD--> 20 DTR--> 20 | Bk --- Y Y 3 RxD--> 2 TxD--> 2 \ R --- Gn Gn 7 GND--- 7 GND--- 7 / Gn --- R R 7 GND--- 7 GND--- 7 | Y --- Bk Bk 2 TxD<-- 3 RxD<-- 3 | Bl --- O O 20 DTR<-- 8 DCD<-- 6 \ Br --- Gy Bl 4 RTS<-- 5 CTS<-- 5 "Page" is the name of one vendor that makes DB-25 to RJ-45 adaptors. For some reason, their internal color coding does not match the cable colors (If someone knows why this is, please tell me). The Page parts are: DB25641M Modular Adaptor Kit 8 Pin/Male DB25641F Modular Adaptor Kit 8 Pin/Female The adaptors, wire connectors, and wire are starting to become available at electronics stores, sadly without any instructions such as these. The famous "Fry's Electronics" store in Sunnyvale calls these adaptors RJ-14 instead of RJ-45 (If somebody knows what the difference is, please tell me). The adaptor contains an RJ-45 socket with 8 wires coming out of it. These wires have RS-232 pins (or sockets as appropriate) crimped onto them. You simply push these pins into the holes in the RS-232 connector and then snap the adaptor housing on. There is one problem, however: the two ground pins have to go into one DB-25 hole (pin 7). You can solder and tape these wires together so they come out to one pin, or you can crimp them together with a simple tiny plastic thingy made by AMP called a "Tel-splice connector 1/2 tap dry", part number 553017-4. So far, this part seems to only be available in 1,000 quantity for $80 or so. Believe me, you want them. (If anyone knows of a source for these in smaller quantities, please tell me.) As you make the adaptors, label them M-DTE, M-DCE, F-DTE, F-DCE, or whatever specialized name goes with a weird device that doesn't fit in these catagories, such as the Sun "MTI" 16-port multiplexer, which uses pin 6 for what it should be doing with pin 8. Is there an RJ-45 adaptor for the IBM-PC 9-pin D connector? If there is, someone please let me know. You will want a couple of tiny RS-232 pin insertion / extraction tools, either the red plastic one with the bronze tip (AMP Part #91067-2) or the cheapy all-plastic red & white one (maker unknown). Yost RS-232 RJ-45 connections September 3, 1987 page 4 The cable crimp tool I have is AMP part number 231652-1 and cost me $108. It is not so easy to find. You will probably have to order it from an industrial telephone equipment distributor. (Many industrial electronic houses will not even recognize the AMP part number as valid). At least two other companies, Palladin and General Machine Products, make an RJ-45 crimp tool, and two hobby companies, GC Electronics and CalRad, are said to be trying to make a low-cost tool (with no success so far). One important missing piece in this plan is an RJ-45 female to female adaptor that has a "twist". This is required if you want to take two cables and connect them together to make a longer cable. Adaptors exist which are either straight through or which do funny connections convenient for telephone systems, but I would like to hear of one that does a simple end-to-end twist. Thanks to folks at UC Berkeley for the idea. Their wiring is slightly different, I gather for historical reasons, but the basic idea was there. If I can find out who really originated this scheme, I'd like to credit him or her by name. Good luck! --dave yost P.S. The remaining four of The Seven* Great RS-232 Hassles: Matching baud rates Transparent Flow control Passing 8 bits of data Slow speed * at least