Wow - my head hurts
From: Ben Scott <[email protected]> To: NT System Admin Issues <[email protected]> Sent: Wednesday, July 27, 2011 10:41 AM Subject: Re: Serial-to-USB Kit On Wed, Jul 27, 2011 at 10:21 AM, <[email protected]> wrote: > ... I'm looking ... for a kit rather than an adapter .. Welcome to the world of RS-232. Buckle up. > ... needing a DB-9 female end, and what I've come across so far is all DB-9 > male ... RS-232 ports are either DCE (Data Communications Equipment) or DTE (Data Terminal Equipment). Classically, DCE was the modem and DTE was the teletype/dumb terminal. Since computers classically connected to a modem and emulated a terminal, computers almost always provide DTE ports. The pinouts of DCE vs DTE connectors are different; the cables are normally straight-through. If one wishes to connect DTE to DTE (or DCE to DCE), one has to used a "null modem" cable/adapter, which switches the pins. It's analogous to a "crossover cable" from Ethernet. Console ports might be either DTE or DCE. (If they're DTE it's easier to connect them to a modem for remote access; if they're DCE it's easier to connect a local terminal. Some designs went one way, some the other.) When it comes to D-subminiature connectors, almost always, DTE ports are male, and DCE ports are female. Given the sexed nature of RS-232 connectors, a straight-through cable or adapter will almost always be male on one side, and female on the other. Null modem adapters/cables will almost always be the same gender on both ends. One occasionally encounters transvestite ports: Female with DTE pinout, or male with DCE pinout. There are 25-pin and 9-pin flavors of both DTE and DCE ports. In almost all cases, we don't care about the extra pins on the 25-pin connectors. So the two sizes are equivalent for our purposes. Given the above, one might normally expect 25-pin/9-pin adapters to be straight-forward, but then things get complicated by adapters which are also null modems or gender changers. > ... RJ-45 console ports ... Be aware that there's no real standard for RS-232 serial on an RJ-45 8-pin connector, so you may need more than one kind of RJ-45/D-subminiature adapter. > Anyone know (part number or catalog number especially welcome) of a kit with > an assortment of modules so that one can plug one of its end pieces to the > end of a cable terminating in a USB at the other end? USB and RS-232 are totally different animals, so there is always going to be an "intelligent" device involved. Since one typically uses a USB/RS-232 adapter on a PC, such adapters almost always present a male DTE port, same as the built-in ports of old. > ... I'm looking ... for a kit rather than an adapter .. Given the above, you're not going to find an easy one-size-fits-all product. Typically one treats these as separate problems: (!) One has an USB/RS-232 adapter to get an RS-232 port on PCs with only USB. (2) One maintains a fleet of RS-232 adapters. Typically: * DCE 25-pin/9-pin * DTE 25-pin/9-pin * 25-pin null modem * 9-pin null modem * 9-pin female/female gender changer * 9-pin male/male gender changer * 25-pin female/female gender changer * 25-pin male/male gender changer Plus whatever RJ-45 variants you need. (3) Given the fleet of adapters, you just need some 9-pin straight cables. Alternatively, some places decide to use UTP RJ-45 straight through everywhere (since they already have it for Ethernet), and put RJ-45-to-D-sub adapters on everything. Are we sufficiently confused yet? -- Ben ~ Finally, powerful endpoint security that ISN'T a resource hog! ~ ~ <http://www.sunbeltsoftware.com/Business/VIPRE-Enterprise/> ~ --- To manage subscriptions click here: http://lyris.sunbelt-software.com/read/my_forums/ or send an email to [email protected] with the body: unsubscribe ntsysadmin ~ Finally, powerful endpoint security that ISN'T a resource hog! ~ ~ <http://www.sunbeltsoftware.com/Business/VIPRE-Enterprise/> ~ --- To manage subscriptions click here: http://lyris.sunbelt-software.com/read/my_forums/ or send an email to [email protected] with the body: unsubscribe ntsysadmin
