hollen@zeta.megatek.uucp (Dion Hollenbeck) (06/22/89)
Serial Protocols I have had several requests to post more information about RS-232 software flow control protocols, notably, XON/XOFF and ETX/ACK. I will, on purpose, not address hardware handshaking methods such as RTS/CTS. Some general questions which have been asked will also be answered. For the most part, standard PC/XT/AT BIOS's do not implement any software flow control protocols (questions about this was what originally prompted this discussion). The BIOS only has the ability to set the UART to a particular baud rate, data bits, stop bits and parity. If any BIOS's implement flow control, I would appreciate hearing about them. There are, however, device drivers which can be installed to implement software flow control and interrupt driven, buffered serial IO. They are available as independent packages as well as part of various C libraries (other languages, too). XON/XOFF XON/XOFF protocol is a protocol implemented using two unprintable ASCII characters, XON = 11h (aka DC1) and XOFF = 13h (aka DC3). This protocol is typically implemented in both directions between terminal and computer, or two computers. It may, however, be only implemented in one direction. For ease of description, let us assume this protocol implemented between a host computer and a terminal which is an output only device (no keyboard) and therefore, the XON/XOFF protocol is implemented in one direction only. We will also assume that the terminal has a buffer of some size (1k for example) and cannot accept and display data as fast as the host can generate it, thus flow control is necessary. It is the responsibility of the terminal to notify the host to stop sending data enough BEFORE the terminal's buffer is full that the host can stop sending before overflowing the terminal's buffer. Generally, two independent processes happen on the host. For simplicity, I will pseudocode them into a simple polled loop, but in reality for efficiency, the check for flow control on the host side would be interrupt driven (not usually done on a PC, but can be). Host send a char function if no input char pending and xoff flag clear send char return WAIT_FOR_XON: if xoff flag set wait until input char rec'd = XON clear xoff flag send char return endif if input char pending get input char if not XOFF buffer for later use send char return else set xoff flag go to WAIT_FOR_XON endif endif It is assumed that there is an overlap when the host may have sent characters to the terminal AFTER the terminal has sent XOFF to the host, but before the host has received it. Therefore, on the terminal's side it is wise to send XOFF to the host when the terminal receive buffer is about 3/4 full. This depends on the size of the buffer, the baud rate, and the latency in the host response to received characters. The terminal is responsible for sending XON to the host when it is again ready to receive more characters. This generally might be when it has emptied its buffer to the 1/4 full mark, thus allowing for overlap and never having an empty buffer. A scheme such as this can keep both the host and the terminal busy as much as possible, and not waste a lot of time in transmission when nothing is being processed. ETX/ACK ETX/ACK protocol is generally used between host computers and printers. Although it may be used in other instances, it generally is not too common. The disadvantage of ETX/ACK is that the host implementation must either know how big a buffer the receiving device has, or only send buffers of a sufficiently small size that it could never overrun a buffer of any device it may be sending to. The other disadvantage is that unlike XON/XOFF which can overlap sending and processing, ETX/ACK leaves very little room for overlap, although some does occur. In the example pseudocode, we will assume a 1k buffer on the device. Host send char function if rec'd char pending get char if char = ACK set ACK flag else buffer char endif endif CHECK_FOR_ACK: if ACK flag set send char increment counter if counter = 800 send ETX clear ACK flag reset counter to 0 endif return else wait for ACK to be rec'd set ACK flag go to CHECK_FOR_ACK endif This means that the host sends a buffer with an ETX (03h) tacked on the end of it. As the printer processes characters, it examines every one to see if it is an ETX. When it receives the ETX, it tosses it and sends the host an ACK (06h) and resumes looking for input characters to process. Once the host has sent the buffer, it must wait until the printer has processed every one of the characters until it can recognize the ETX and send and ACK. This reduces the amount of overlap in sending that can occur. The only overlap can occur while the host is sending the buffer. The printer has no way to inform the host to begin sending again while it still has some buffer left to process, it must empty the buffer before starting the hsot again. Question received > Other than XON/XOFF and ETX/ACK, are there any other "common" > protocols? (i.e - I have heard of STX/ETX = start of > text / end of text). Not including hardware handshaking, not to my knowledge. STX/ETX are markers which are commonly used to surround a block of transmitted data for purposes of indicating block start and end. Typically used so that a block can be check-summed and re-transmitted if necessary. Just keep in mind that in dealing with RS232, there are no hard and fast rules. The RS232 "standard" is merely a document which designates the accepted use of the 25 wires in a cable and the physical configuration of the size and shape of the connector (DB-25). Many implementors make unique use of the signals on the wires, and of the data sent over them. There are some commonly accepted followed conventions, but always be aware of someone having implemented them "almost" like you would expect. I hope that this primer will be useful to many of you out there. Do not hesitate to mail me directly with questions. If there are such questions of general interest, I will post follow-ups to the net so all can benefit. Dion Hollenbeck (619) 455-5590 x2814 Megatek Corporation, 9645 Scranton Road, San Diego, CA 92121 seismo!s3sun!megatek!hollen ames!scubed/
barmar@think.COM (Barry Margolin) (06/23/89)
In article <589@megatek.UUCP> hollen@megatek.UUCP () writes: > XON/XOFF > Therefore, on the terminal's >side it is wise to send XOFF to the host when the terminal receive >buffer is about 3/4 full. This depends on the size of the buffer, >the baud rate, and the latency in the host response to received >characters. Unfortunately, host latency can vary widely. This is the most serious problem with the XON/XOFF protocol; if the terminal assumes that the host can respond to the XOFF faster than it actually can, the terminal's buffer will overflow. Some recent terminals allow the user to set the XOFF threshhold in the SET-UP menu, but many terminals and emulators don't. My friends at school used to refer to XON/XOFF as the "help! I'm drowning" protocol; if the lifeguard doesn't notice you until you're going down for the third time, you'd better hope he's a fast swimmer. > ETX/ACK > Once the host has sent the buffer, it must wait until the >printer has processed every one of the characters until it can recognize >the ETX and send and ACK. This reduces the amount of overlap in sending >that can occur. High throughput is typically achieved with using ETC/ACK by employing "double buffering". This is a very simple form of what is known as "windowing" in the context of network transport protocols. If the printer is believed to have an N-byte buffer, you send an ETX after every N/2 bytes. The sender is permitted to continue transmitting when there is one ETX that hasn't been ACKed, but it stops sending if it gets to the second ETX without having seen an ACK. ETX/ACK with double buffering permits the most efficient use of the bandwidth without running the risk of overflowing the printer's buffer. One problem I've seen with ETX/ACK, though, is that some printers don't implement it very well. We had an NEC SpinWriter that didn't recognize ETX if it was inserted into the middle of an escape sequence. Our application used escape sequences heavily (it implemented bidirectional printing by sending appropriate escape sequences at the end of each line), while the ETX/ACK was implemented in the bowels of the OS terminal driver, which knows nothing about escape sequences sent by the caller. From time to time the printer would just stop until someone manually typed Control-F (ACK) on its keyboard. Barry Margolin Thinking Machines Corp. barmar@think.com {uunet,harvard}!think!barmar
dmt@mtunb.ATT.COM (Dave Tutelman) (06/23/89)
In article <589@megatek.UUCP> hollen@megatek.UUCP () writes: > > Serial Protocols Thanks, Dion, for a really good tutorial! The only nit I'd like to pick is your subject line's suggestion that this has anything to do with RS-232. (The retitling to "serial protocols" is appropriate, and "asynchronous protocols" or "ASCII protocols" would be even more so.) In fact, your comment about the RS-232 standard itself needs some corrections... > The RS232 "standard" is merely a document which designates >the accepted use of the 25 wires in a cable and the physical configuration >of the size and shape of the connector (DB-25). Why is the word STANDARD in quotes? There is, in fact, a REAL LIVE EIA standard, designated RS-232-C and dated 1981. (Originally 1969, reaffirmed 1981.) It DOES NOT specify the DB-25 interface connector, or any interface connector at all. It DOES specify: - Scope of applicability (e.g.- speeds to 20 kilobits/sec). - Electrical characteristics (e.g.- driver & receiver voltages and impedances). - Functional descriptions of the leads, including extensive "rules" of how they MUST be used (to comply with the standard). - Some standard subsets of the full 25-lead interface. >Many implementors make >unique use of the signals on the wires, and of the data sent over them. >There are some commonly accepted followed conventions, but always be >aware of someone having implemented them "almost" like you would expect. Most of the "conventions" to which you refer are in fact specified by the functional rules in RS-232-C. Some of the "unique uses" are in direct violation of the standard, though most are permitted (or even encouraged, if you read the standard closely). Once again, thanks for a really good tutorial on asynchronous ASCII protocols (which have nothing to do with RS-232). +---------------------------------------------------------------+ | Dave Tutelman | | Physical - AT&T Bell Labs - Middletown, NJ | | Logical - ...att!mtunb!dmt | | Audible - (201) 957 6583 | +---------------------------------------------------------------+
bmiller@PRC.Unisys.COM (Bruce J. Miller) (06/24/89)
In article <1538@mtunb.ATT.COM> dmt@mtunb.UUCP (Dave Tutelman) writes: >In article <589@megatek.UUCP> hollen@megatek.UUCP () writes: > >In fact, your comment about the RS-232 standard itself needs some >corrections... > >> The RS232 "standard" is merely a document which designates >>the accepted use of the 25 wires in a cable and the physical configuration >>of the size and shape of the connector (DB-25). > >Why is the word STANDARD in quotes? There is, in fact, a REAL LIVE >EIA standard, designated RS-232-C and dated 1981. (Originally 1969, >reaffirmed 1981.) It DOES NOT specify the DB-25 interface connector, >or any interface connector at all.... ANSI/EIA RS-232-D, issued January 1987, now specifies not only the physical connector, but also such esoteric things as "finger clearance" (i.e., how close together you can put RS-232 25 pin D connectors so you can get the cables on and off). Bruce Miller (bmiller@burdvax.prc.unisys.com) <Insert virus code here> Vacuum tubes are not dead - they just smell that way.
hollen@zeta.megatek.uucp (Dion Hollenbeck) (06/24/89)
From article <1538@mtunb.ATT.COM>, by dmt@mtunb.ATT.COM (Dave Tutelman): > In article <589@megatek.UUCP> hollen@megatek.UUCP () writes: > [ ... stuff about titleing deleted ... ] > In fact, your comment about the RS-232 standard itself needs some > corrections... > >> The RS232 "standard" is merely a document which designates >>the accepted use of the 25 wires in a cable and the physical configuration >>of the size and shape of the connector (DB-25). > > Why is the word STANDARD in quotes? There is, in fact, a REAL LIVE > EIA standard, designated RS-232-C and dated 1981. (Originally 1969, > reaffirmed 1981.) It DOES NOT specify the DB-25 interface connector, > or any interface connector at all. It DOES specify: > > [ ... lots of good observations deleted ...] Thank you for clarifying this to the net, Dave. I do, in fact, have a copy of the very standard you mention, but in my humble experience, I have seen it violated more often than followed. Therefore, I put the word STANDARD in quotes. In the hardware we build here, we do our best to adhere to such standards when they exist, but this is, unfortunately, not the case with many manufacturers. And yes, I am wrong about the standard specifying the size and shape of the connector. I was talking off the top of my head and obviously spliced into the standard pages from other documents which do not belong there without realizing I was doing so. This merely points out that even the "experts" can give mis-information in the process of being helpful. Generally stems from having too much information in the head and not realizing that it should be looked up. Sorry if I caused any confusion, and thanks to all for the corrections which have been mentioned. The important thing is that people out there get the correct information. Dion Hollenbeck (619) 455-5590 x2814 Megatek Corporation, 9645 Scranton Road, San Diego, CA 92121 uunet!megatek!hollen or hollen@megatek.uucp
ken@cs.rochester.edu (Ken Yap) (06/24/89)
|> Why is the word STANDARD in quotes? There is, in fact, a REAL LIVE |> EIA standard, designated RS-232-C and dated 1981. (Originally 1969, |> reaffirmed 1981.) It DOES NOT specify the DB-25 interface connector, |> or any interface connector at all. It DOES specify: One reason the standard is dated is that it only talks about DCEs and DTEs. Many real world devices are hard to classify either way. Is a computer a DCE or a DTE. If I connect a terminal to a mainframe, it should look like a DCE, right? But what if I have a PC and dial out with a modem? Shouldn't it be a DTE then? What about a printer? A DTE, of course. OK, but what about hardware flow control? The RTS/CTS lines are intended to the modem to tell the terminal when to send. But in this case it is the printer that should tell the computer when it is ready to receive. And on it goes. To add to the confusion, many terminal manufacturers (DEC especially) use the opposite type of connector from what most other people use. And yes, the standard doesn't specify a connector so in principle computers with 9 pin connectors are conforming, if irritating. The problem is simply that the standard is inadequate for all the uses it has been pressed into. It's a miracle things work together at all. All of these problems can be solved with a little detective work. I recommend the book The RS232 Solution (I think) for anybody who will be dealing with RS232 interfacing in a big way. You thought a set of straight through and null modem cables would solve your problems? Read the book and learn how cables with too many wires connected can actually prevent the interface from working. Sorry I've strayed from the original subject, which is really about software flow control, but hardware handshaking is a big headache too.
rbthomas@athos.rutgers.edu (Rick Thomas) (06/24/89)
The referenced posting deliberately did NOT talk about hardware flow
control.
Could you do another posting on that subject please?
Thanks in advance!
Rick
--
Rick Thomas
uucp: {ames, cbosgd, harvard, moss, seismo}!rutgers!jove.rutgers.edu!rbthomas
arpa: rbthomas@JOVE.RUTGERS.EDU
Phone: (201) 932-4301markz@ssc.UUCP (Mark Zenier) (06/25/89)
> |> Why is the word STANDARD in quotes? There is, in fact, a REAL LIVE > |> EIA standard, designated RS-232-C and dated 1981. (Originally 1969, > |> reaffirmed 1981.) It DOES NOT specify the DB-25 interface connector, > |> or any interface connector at all. It DOES specify: The sex of the connector. "Section Three 3. Interface Mechanical Characteristics 3.1 The interface between the data terminal equipment and the data communications equipment is located at a pluggable connector signal interface point between the two equipments. The female connector shall be associated with, but not necessarily physically attached to the data communications equipment..." In article <1989Jun24.005740.19326@cs.rochester.edu>, ken@cs.rochester.edu (Ken Yap) writes: > To add to the confusion, many terminal manufacturers (DEC especially) > use the opposite type of connector from what most other people use. And > yes, the standard doesn't specify a connector so in principle computers > with 9 pin connectors are conforming, if irritating. Dec and Zenith and very few others get it right, and put a male connector on their DTE ports. Lear Seigler, Qume, and every japanese printer manufacturer I've seen need a sex education lesson. Mark Zenier uunet!nwnexus!pilchuck!ssc!markz markz@ssc.uucp uunet!amc! -- Mark Zenier uunet!nwnexus!pilchuck!ssc!markz markz@ssc.uucp uunet!amc!
mcdonald@uxe.cso.uiuc.edu (06/26/89)
> |> Why is the word STANDARD in quotes? There is, in fact, a REAL LIVE > |> EIA standard, designated RS-232-C and dated 1981. (Originally 1969, > |> reaffirmed 1981.) It DOES NOT specify the DB-25 interface connector, > |> or any interface connector at all. It DOES specify: >The sex of the connector. >3.1 The interface between the data terminal equipment and the data >communications equipment is located at a pluggable connector signal interface >point between the two equipments. The female connector shall be associated >with, but not necessarily physically attached to the data communications >equipment..." What's a DCE or a DTE? I never use those words. To be a useful standard, it should specify the sex of the connector for each particular type of equipment, by its common name: 1. Computers - odd, it never seems to mention computers!!!! 2. Terminals - Presumably computers and terminals should be the same sex. 3. Printers 4. Modems 5. Scanners 6. Data collection equipment (voltmeters, etc.) - presumably the same as scanners 7. whatever else people can think of And, of course, the question of the function of pins 2 and 3 has to be worked out!!! Doug McDonald
hollen@zeta.megatek.uucp (Dion Hollenbeck) (06/26/89)
From article <Jun.24.01.51.56.1989.23986@athos.rutgers.edu>, by rbthomas@athos.rutgers.edu (Rick Thomas): > The referenced posting deliberately did NOT talk about hardware flow > control. > > Could you do another posting on that subject please? > Can somebody else possibly do this? We have deliberately avoided dealing with hardware flow control since it is implemented in so many different ways, and besides, the devices we talk to typically, are input only. Dion Hollenbeck (619) 455-5590 x2814 Megatek Corporation, 9645 Scranton Road, San Diego, CA 92121 uunet!megatek!hollen or hollen@megatek.uucp
henry@utzoo.uucp (Henry Spencer) (06/26/89)
In article <1954@ssc.UUCP> markz@ssc.UUCP (Mark Zenier) writes: >"3.1 The interface between the data terminal equipment and the data >communications equipment is located at a pluggable connector signal interface >point between the two equipments. The female connector shall be associated >with, but not necessarily physically attached to the data communications >equipment..." > >Dec and Zenith and very few others get it right, and put a male connector >on their DTE ports. Lear Seigler, Qume, and every japanese printer >manufacturer I've seen need a sex education lesson. Ah, but note the wording in the quoted section carefully. It says that the interface occurs at *one* interface point, where the DCE shall have a female connector. It says nothing about what's on the other end of the cable. In fact, the original rule was that the cable was supposed to come with the DTE, making sex of connector (if any) at the DTE end unimportant. Mind you, it still makes sense that *if* you have a connector at the DTE end, it rationally ought to be male, but this isn't formally required. Actually, if one wants to be rational about it, equipment ought to have male RS232 connectors whenever physically possible. The way these particular connectors are built, the male connectors are much more durable (solid post, as opposed to the springy sleeve on the female end), so they ought to be used in the position where the connector is harder to replace. That is, on the equipment rather than the cable. (If you've ever wondered why VME backplane connectors are "inverse DIN", with male on backplane and female on board, that's why.) -- NASA is to spaceflight as the | Henry Spencer at U of Toronto Zoology US government is to freedom. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
phil@diablo.amd.com (Phil Ngai) (06/27/89)
In article <1989Jun24.005740.19326@cs.rochester.edu> ken@cs.rochester.edu (Ken Yap) writes: |To add to the confusion, many terminal manufacturers (DEC especially) |use the opposite type of connector from what most other people use. And I beg to differ. DEC and IBM are some of the best vendors in terms of complying with what there is of the RS-232 spec and their use of a male connector is correct. What do you think DTE stands for? Data Terminal Equipment. Doesn't a terminal sound as though it should be classified as DTE? Just because HP and Wyse and Televideo and Adds get it wrong doesn't mean everyone should do it wrong. -- Phil Ngai, phil@diablo.amd.com {uunet,decwrl,ucbvax}!amdcad!phil "The government is not your mother."
barton@holston.UUCP (barton) (06/27/89)
Get this: I ordered an Epson LQ-1050 printer, which according to
the doc's comes with a "standard" RS-232C serial interface, only
to find out that the so called "standard" interface is actually
a 6 pin DIN connector! I wonder which standard they are refering
to?
--
Barton A. Fisk | UUCP: {texbell,uunet}!warble!holston!barton
PO Box 1781 | DOMAIN: barton@holston
Lake Charles, La. 70602 | ----------------------------------------
318-439-5984 | +++++ "Hal, open the pod bay doors" --- Davesteve@arc.UUCP (Steve Savitzky) (06/28/89)
In article <45900244@uxe.cso.uiuc.edu> mcdonald@uxe.cso.uiuc.edu (Doug McDonald) writes: > >What's a DCE or a DTE? I never use those words. To be a useful standard, >it should specify the sex of the connector for each particular type >of equipment, by its common name: [list of random equipment deleted] DCE = Data Communication Equipment = modem, cable, or whatever DTE = Data Terminal Equipment = CRT, computer, or whatever. Terminal, in this case, means something that "terminates" a connection, that is, the thing at the end of the line. Like bus terminal. The standard is written so that you can take a computer or terminal and connect it directly (or via a 1-1 male-female extension cord) to a modem. Connector sex is specified (I don't remember which is which). >And, of course, the question of the function of pins 2 and 3 has to be >worked out!!! Pin 2 = Transmitted data (DTE -> DCE) Pin 3 = Received data (DTE <- DCE) A cable with same-sex connectors and pins 2 and 3 swapped is called a "Null Modem" because it replaces two modems and a telephone system, letting you connect two DTE's. There are two flavors of null modem depending on whether you cross-connect the modem control signals so the two DTE's can play flow-control games, or loop them back because one or both of them is too stupid to handle them correctly. A lot of the unstandardness of connectors called "RS232" comes from microcomputer manufacturers who didn't understand the standard making the connectors on their computers look like DCE's so that you could connect a terminal to the computer using a 1-1 cable, usually made with ribbon cable and press-on connectors. Now, of course, it's hard to tell what you're going to meet up with. I always have a set of male-male, female-female, and both kinds of null modem adaptors handy. Doesn't everybody? -- Steve Savitzky | apple.com!arc!steve ADVANsoft Research Corp. | (408)727-3357 4301 Great America Parkway | #include<disclaimer.h> Santa Clara, CA 95054 | May the Source be with you!
pritch@cheops.cis.ohio-state.edu (Norm Pritchett) (06/28/89)
In article <32@holston.UUCP> barton@holston.UUCP (barton) writes: >Get this: I ordered an Epson LQ-1050 printer, which according to >the doc's comes with a "standard" RS-232C serial interface, only >to find out that the so called "standard" interface is actually >a 6 pin DIN connector! I wonder which standard they are refering >to? Why, RS-232-C of course! Which, incidentally, doesn't require a particular connector type (that's not until RS-232-D). The claim isn't that the connector is a standard one but that the signals in the connector are (they gotcha!). -=- Norm Pritchett, The Ohio State University College of Engineering Network Internet: pritchett@eng.ohio-state.edu BITNET: TS1703 at OHSTVMA UUCP: pritch@sydney.columbus.oh.us CCNET: ENG::PRITCHETT (6172::PRITCHETT)
sme@computing-maths.cardiff.ac.uk (Simon Elliott) (06/29/89)
In article <1989Jun26.155855.1680@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes: > ... The way these > particular connectors are built, the male connectors are much more > durable (solid post, as opposed to the springy sleeve on the female end), > so they ought to be used in the position where the connector is harder > to replace. Now I am confused. I always thought that the male connector was the one with the pins, rather than the sockets. It's been a long day, and I may be reading Henry's article incorrectly, but he seems to be saying that the solid block with the sockets in it is male, and that the flimsy shell with the pins in it is female. Do I need a basic biology lesson? -- -------------------------------------------------------------------------- Simon Elliott Internet: sme%v1.cm.cf.ac.uk@nsfnet-relay.ac.uk UWCC Computer Centre JANET: sme@uk.ac.cf.cm.v1 40/41 Park Place UUCP: {backbones}!mcvax!ukc!reading!cf-cm!sme Cardiff, Wales PHONE: +44 222 874300
leonard@bucket.UUCP (Leonard Erickson) (06/29/89)
In article <45900244@uxe.cso.uiuc.edu> mcdonald@uxe.cso.uiuc.edu writes:
<What's a DCE or a DTE? I never use those words. To be a useful standard,
<it should specify the sex of the connector for each particular type
<of equipment, by its common name:
<1. Computers - odd, it never seems to mention computers!!!!
<
<2. Terminals - Presumably computers and terminals should be the same
< sex.
<
<3. Printers
<
<4. Modems
<
<5. Scanners
<
<6. Data collection equipment (voltmeters, etc.) - presumably the same as
< scanners
<
<7. whatever else people can think of
<
<And, of course, the question of the function of pins 2 and 3 has to be
<worked out!!!
DCE = Data Communication Equipment (ie modems)
DTE = Data Terminal Equipment (ie terminals & computers)
The function of pins 2&3 is determined by whether an item is DTE or DCE.
Printers, scanners, etc are not covered. The standard was intended only
for connections between terminals anmd modems or modems and computers.
Anything else is a use that has been more or less kludged onto a
convenient standard that was never intended to handle it.
--
Leonard Erickson ...!tektronix!reed!percival!bucket!leonard
CIS: [70465,203]
"I'm all in favor of keeping dangerous weapons out of the hands of fools.
Let's start with typewriters." -- Solomon Shortprc@erbe.se (Robert Claeson) (06/29/89)
In article <45900244@uxe.cso.uiuc.edu> mcdonald@uxe.cso.uiuc.edu writes: >What's a DCE or a DTE? I never use those words. To be a useful standard, >it should specify the sex of the connector for each particular type >of equipment, by its common name: DTE stands for Data Terminal Equipment, where "Terminal" can be thought of as a "Termination" of a RS-232-C connection. Thus, computers, printers, terminal servers, terminals, lab equipment etc all are DTE's. A DCE is a Data Communication Equipment that serves as a means to connect two DTE's to each other. A typical DCE is a modem. DTE's have male and DCE's have female connectors. >1. Computers - odd, it never seems to mention computers!!!! DTE >2. Terminals - Presumably computers and terminals should be the same > sex. DTE >3. Printers DTE >4. Modems DCE >5. Scanners DTE >6. Data collection equipment (voltmeters, etc.) - presumably the same as > scanners DTE >7. whatever else people can think of DTE (mostly)/DCE (in some cases) -- Robert Claeson E-mail: rclaeson@erbe.se ERBE DATA AB
dmt@mtunb.ATT.COM (Dave Tutelman) (06/29/89)
In article <32@holston.UUCP> barton@holston.UUCP (barton) writes: > >Get this: I ordered an Epson LQ-1050 printer, which according to >the doc's comes with a "standard" RS-232C serial interface, only >to find out that the so called "standard" interface is actually >a 6 pin DIN connector! I wonder which standard they are refering >to? Barton, As I posted previously, the 232-C standard DOESN'T specify the connector. (I am told that the newer RS-232-D does, but I haven't seen it; anyway, your supplier said "C".) The standard DOES list (in Section Five) a collection of 14 subsets of the full 25-lead interface, which are allowable standard interfaces. Several of them use six or fewer leads. Thus there's nothing in the use of a 6-pin DIN connector to prevent it from complying with the RS-232-C standard. +---------------------------------------------------------------+ | Dave Tutelman | | Physical - AT&T Bell Labs - Middletown, NJ | | Logical - ...att!mtunb!dmt | | Audible - (201) 957 6583 | +---------------------------------------------------------------+
michaelk@copper.MDP.TEK.COM (Michael D. Kersenbrock) (07/01/89)
<> ... The way these <> particular connectors are built, the male connectors are much more <> durable (solid post, as opposed to the springy sleeve on the female end), <> so they ought to be used in the position where the connector is harder <> to replace. < <Now I am confused. I always thought that the male connector was the one <with the pins, rather than the sockets. It's been a long day, and I may be <reading Henry's article incorrectly, but he seems to be saying that the solid <block with the sockets in it is male, and that the flimsy shell with the pins <in it is female. Do I need a basic biology lesson? No, but he is right in a way. The plug with "pins" has male connectors located in a female connector housing. Note that the "housing" IS female! Likewise the other half has female connection-pins in a male housing! When I say housing, what I mean is that if you removed the electrical connection parts, you still could mate the connector housings, look at them and figure out their sex. Most people seem to call a connector "male" if it has male pins, but being a stickler for such things, I call it "the female connector with male pins" (which is most correct along with other paraphrases of the same thing). If you "build" connectors from some manufacturers, you can have both male and female pins in a housing of either sex, or a hermaphroditic housing. Almost as tricky as life, eh? -- Mike Kersenbrock Tektronix Microprocessor Development Products michaelk@copper.MDP.TEK.COM Aloha, Oregon
pnelson@antares.UUCP (Phil Nelson) (07/01/89)
In article <821@cf-cm.UUCP> sme@computing-maths.cardiff.ac.uk (Simon Elliott) writes: |In article <1989Jun26.155855.1680@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes: || ... The way these || particular connectors are built, the male connectors are much more || durable (solid post, as opposed to the springy sleeve on the female end), || so they ought to be used in the position where the connector is harder || to replace. | |Now I am confused. I always thought that the male connector was the one |with the pins, rather than the sockets. It's been a long day, and I may be |reading Henry's article incorrectly, but he seems to be saying that the solid |block with the sockets in it is male, and that the flimsy shell with the pins |in it is female. Do I need a basic biology lesson? No, you're right. Henry is wrong. Amazing, isn't it? |-- |-------------------------------------------------------------------------- |Simon Elliott Internet: sme%v1.cm.cf.ac.uk@nsfnet-relay.ac.uk |UWCC Computer Centre JANET: sme@uk.ac.cf.cm.v1 |40/41 Park Place UUCP: {backbones}!mcvax!ukc!reading!cf-cm!sme |Cardiff, Wales PHONE: +44 222 874300 -- Phil Nelson at (but not speaking for) OnTyme:NSC.P/Nelson Tymnet, McDonnell Douglas Network Systems Company Voice:408-922-7508 UUCP:{pyramid|ames}oliveb!tymix!pnelson LRV:Component Station "What we face is government troops and we have no guns." -Chinese student
Ralf.Brown@B.GP.CS.CMU.EDU (07/01/89)
In article <471@antares.UUCP>, pnelson@antares.UUCP (Phil Nelson) writes: }In article <821@cf-cm.UUCP> sme@computing-maths.cardiff.ac.uk (Simon Elliott) writes: }|In article <1989Jun26.155855.1680@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes: }|| ... The way these }|| particular connectors are built, the male connectors are much more }|| durable (solid post, as opposed to the springy sleeve on the female end), }|| so they ought to be used in the position where the connector is harder }|| to replace. }| }|Now I am confused. I always thought that the male connector was the one }|with the pins, rather than the sockets. It's been a long day, and I may be }|reading Henry's article incorrectly, but he seems to be saying that the solid }|block with the sockets in it is male, and that the flimsy shell with the pins }|in it is female. Do I need a basic biology lesson? } } No, you're right. Henry is wrong. Amazing, isn't it? Henry is right, you've both misread him. He was talking about the thin metal sleeves INSIDE the solid block of a female connector. If one of them gets bent out of shape, the corresponding pin of the male connector will not make proper contact. On the other hand, in the unlikely event that a pin on the male end should get bent, you can always use a screwdriver to bend it back into place.... -- UUCP: {ucbvax,harvard}!cs.cmu.edu!ralf -=-=-=- Voice: (412) 268-3053 (school) ARPA: ralf@cs.cmu.edu BIT: ralf%cs.cmu.edu@CMUCCVMA FIDO: Ralf Brown 1:129/46 Disclaimer? I claimed something? "When things start going your way, it's usually because you stopped going the wrong way down a one-way street."
henry@utzoo.uucp (Henry Spencer) (07/02/89)
In article <821@cf-cm.UUCP> sme@computing-maths.cardiff.ac.uk (Simon Elliott) writes: >> ... the male connectors are much more >> durable (solid post, as opposed to the springy sleeve on the female end), > >Now I am confused. I always thought that the male connector was the one >with the pins, rather than the sockets. It's been a long day, and I may be >reading Henry's article incorrectly, but he seems to be saying that the solid >block with the sockets in it is male, and that the flimsy shell with the pins >in it is female. Do I need a basic biology lesson? No, just a good night's sleep. :-) I was talking about the contacts themselves, not about the shell containing them. The shells are pretty durable on either side. One reason why the female contacts are imbedded in a solid block is that they *need* the support -- they really are much flimsier than the male contacts, which can stand on their own. (It should be noted that this isn't a biological necessity. :-) There has to be spring action to get proper wiping action when the contacts mate, but in principle you could put a springy bulge on the male pin and have the female sleeve solid and robust. Such contacts do exist -- the banana plugs used for test leads, for example -- but they're not too common nowadays.) -- $10 million equals 18 PM | Henry Spencer at U of Toronto Zoology (Pentagon-Minutes). -Tom Neff | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
terryk@pinocchio.Encore.COM (Terence Kelleher) (07/02/89)
In article <3279@copper.MDP.TEK.COM> michaelk@copper.MDP.TEK.COM.UUCP (Michael D. Kersenbrock writes: > >Most people seem to call a connector "male" if it has male pins, but >being a stickler for such things, I call it "the female connector with >male pins" (which is most correct along with other paraphrases of the >same thing). > Boy, this is getting to be confusing. Shows the need for sex ed. in our public schools. :-) The manufaccturers more typically refer to the mating connectors as PIN and SOCKETS. Part numbers for the 25 pin D shell are generally 25-S or 25-P to show which side you have. This eliminates all the difficult (and sexist) problems. The references are always to the electrical connector and not to the housing. Sorry Mike, but designations like "the female connector with male pins" are not very clear and certainly not the commonly understood designations in the industry. Terry Kelleher Terry Kelleher, Encore Computer Phone: 508-460-0500 UUCP: {bu-cs,decvax,necntc,talcott}!encore!terryk Internet: terryk%pinocchio@multimax.ARPA
pnelson@antares.UUCP (Phil Nelson) (07/05/89)
|In article <471@antares.UUCP>, pnelson@antares.UUCP (Phil Nelson) writes: |}In article <821@cf-cm.UUCP> sme@computing-maths.cardiff.ac.uk (Simon Elliott) writes: |}|In article <1989Jun26.155855.1680@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes: |}|| ... The way these |}|| particular connectors are built, the male connectors are much more |}|| durable (solid post, as opposed to the springy sleeve on the female end), |}|| so they ought to be used in the position where the connector is harder |}|| to replace. |}| |}|Now I am confused. I always thought that the male connector was the one |}|with the pins, rather than the sockets. It's been a long day, and I may be |}|reading Henry's article incorrectly, but he seems to be saying that the solid |}|block with the sockets in it is male, and that the flimsy shell with the pins |}|in it is female. Do I need a basic biology lesson? |} |} No, you're right. Henry is wrong. Amazing, isn't it? | |Henry is right, you've both misread him. He was talking about the thin metal |sleeves INSIDE the solid block of a female connector. If one of them gets |bent out of shape, the corresponding pin of the male connector will not make |proper contact. On the other hand, in the unlikely event that a pin on the |male end should get bent, you can always use a screwdriver to bend it back |into place.... You're right, I misread Henry's article (sorry, Henry). I thought that what was being said was that the female connector should be on equipment, not the male. My experience is that the female DB-25 connector is more durable than the male, precisely because the "sleeves" are recessed within the connector block. The male connector is subject to bent pins, which can only be straightened very few times before they break, split pins (most pins are made in two halves, pressed together, these can split at the tip, creating a "V" which can snag the edge of the "sleeves" in the socket), and bent shells. Those installations where the where the male connector is recessed within the equipment are not subject to the bent shells, but the first two still apply. I have dealt with quite a few of these connectors, and I have never had to replace a "sleeve" on a female connector, I have replaced bent and broken pins on the male connectors. In ideal conditions, I suppose the male connector will last longer, because it has no spring to lose tension over time, in the real world (the one I work in, at least), rough treatment damages more male connectors. By the way, does anyone know how long the spring lasts? |-- |UUCP: {ucbvax,harvard}!cs.cmu.edu!ralf -=-=-=- Voice: (412) 268-3053 (school) |ARPA: ralf@cs.cmu.edu BIT: ralf%cs.cmu.edu@CMUCCVMA FIDO: Ralf Brown 1:129/46 -- Phil Nelson at (but not speaking for) OnTyme:NSC.P/Nelson Tymnet, McDonnell Douglas Network Systems Company Voice:408-922-7508 UUCP:{pyramid|ames}oliveb!tymix!pnelson LRV:Component Station If IBM is '1984', Apple is 'Brave New World'
vail@tegra.UUCP (Johnathan Vail) (07/06/89)
In article <1989Jul1.230627.28355@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes: In article <821@cf-cm.UUCP> sme@computing-maths.cardiff.ac.uk (Simon Elliott) writes: >> ... the male connectors are much more >> durable (solid post, as opposed to the springy sleeve on the female end), > >Now I am confused. I always thought that the male connector was the one >with the pins, rather than the sockets. It's been a long day, and I may be >reading Henry's article incorrectly, but he seems to be saying that the solid >block with the sockets in it is male, and that the flimsy shell with the pins >in it is female. Do I need a basic biology lesson? No, just a good night's sleep. :-) I was talking about the contacts The gender way of describing these things is really confusing. I prefer the way that the connectors describe themselves: DB-25P or DB-25S for Pins or Sockets. That way you know what you have and don't have to figure out if someone means the actual little pins are male or the shell is.... "Frisbeetarianism is the belief that when you die, your soul goes up on the roof and gets stuck." -- button _____ | | Johnathan Vail | tegra!N1DXG@ulowell.edu |Tegra| (508) 663-7435 | N1DXG@145.110-,145.270-,444.2+,448.625- -----