Post by thread:[OT]: History of the PC parallel port

>Specifically, I'd like to find out which version of the IBM PC >family first included a parallel port. As far as I can tell, >this was the IBM 5170 PC/AT, released in 1984. What do you class as a parallel port? Are you talking about a printer port, because the very original IBM PC had a printer port, often on the monochrome video card, as there was no port on the motherboard. The original port also had a bidirectional data bus, although that was not part of the specification as such. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Alan, Hmmm. Sounds as though this is even more complicated than I had expected. What I am actually interested in is the port referred to as "LPT1" (or LPT2, 3, etc) in a recent PC, and connected to a printer via a Centronics interface. These ports are accessed via three sequential port addresses (usually starting at 0x0378 if there is only one port). Michael. {Original Message removed}

>What I am actually interested in is the port referred to as "LPT1" >(or LPT2, 3, etc) in a recent PC, and connected to a printer via >a Centronics interface. These ports are accessed via three >sequential port addresses (usually starting at 0x0378 if there is >only one port). Exactly, and that is what was on the monochrome card. To be pedantic the base address of the port on the monochrome card was at 3C8 (IIRC) and the cards that were available to fit a printer port if you did not have a monochrome card were switchable to two other addresses that I cannot remember off hand, and appeared as LPT1 and LPT2 pushing the monochrome card address to LPT3 if it was still fitted. In short the IBM PC has always had a printer port available, but because it was always on a plug in card of some sort, then it may not have always been fitted. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Michael Pont wrote: > Alan, > > Hmmm. Sounds as though this is even more complicated than I had expected. > > What I am actually interested in is the port referred to as "LPT1" (or LPT2, > 3, etc) in a recent PC, and connected to a printer via a Centronics > interface. These ports are accessed via three sequential port addresses > (usually starting at 0x0378 if there is only one port). > > Michael. Want to make things more interesting? Microcomputers (such as those running OS9 or FLEX) used to have male DB25 for parallel and female for RS232. The PC drove me nuts when it came out. Cabling was a nightmare (was it going to be used with a PC or a terminal et.). I've also played with printing machines which supposedly dated back to ~1948 that used the exact same pinning on a DB25 as was used for centronics printers but the voltages where like that of RS232 (+/- 25V DC). Please take the last part with a grain of salt as I have no idea if the 1948 date was true or not. -- Linux Home Automation Neil Cherry spam_OUTncherryTakeThisOuTcomcast.net http://mywebpages.comcast.net/ncherry/ (Text only) http://linuxha.sourceforge.net/ (SourceForge) http://hcs.sourceforge.net/ (HCS II) -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> Exactly, and that is what was on the monochrome card. To be pedantic the > base address of the port on the monochrome card was at 3C8 (IIRC) and the Sorry to nitpick but the base address was 0x3BC. TTYL -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Many thanks for all the useful replies - much appreciated! Michael. ----- Original Message ----- From: "Alan B. Pearce" <.....A.B.PearceKILLspam@spam@RL.AC.UK> To: <PICLISTKILLspamMITVMA.MIT.EDU> Sent: Monday, March 24, 2003 11:04 AM Subject: Re: [OT]: History of the PC parallel port {Quote hidden}> >What I am actually interested in is the port referred to as "LPT1" > >(or LPT2, 3, etc) in a recent PC, and connected to a printer via > >a Centronics interface. These ports are accessed via three > >sequential port addresses (usually starting at 0x0378 if there is > >only one port). > > Exactly, and that is what was on the monochrome card. To be pedantic the > base address of the port on the monochrome card was at 3C8 (IIRC) and the > cards that were available to fit a printer port if you did not have a > monochrome card were switchable to two other addresses that I cannot > remember off hand, and appeared as LPT1 and LPT2 pushing the monochrome card > address to LPT3 if it was still fitted. > > In short the IBM PC has always had a printer port available, but because it > was always on a plug in card of some sort, then it may not have always been > fitted. > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Hej Michael Pont. Tack för ditt meddelande 07:40 2003-03-25 enligt nedan: >Many thanks for all the useful replies - much appreciated! My 2 oere, from memory, i read somewhere, you should check if it is OK!! 1) The origial Centronics parallel interface had differential signalling (or was i tjust separate ground for each signal) thus the many pins. 2) centronics could adress 255 devices on the same port, using a signal indicating that the data was an adress. The PC LPT is really crappy in comparison...! Also, IIRC BIOS/reserved adress range support four LPT, but MS-DOS and Windows only 3, I don´t know how about other PC OS:es. /Morgan -- Morgan Olsson, Kivik, Sweden -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

>1) The origial Centronics parallel interface had differential >signalling (or was i tjust separate ground for each signal) >thus the many pins. It was a ground for each pin, so it made it real easy to use twisted pair cables. In one instance where a customer wanted a printer the other side of a corridor this fact allowed us to run a cable through the ceiling without any problems on a Centronics interface. >2) centronics could adress 255 devices on the same port, >using a signal indicating that the data was an adress. No this is not the case. This sounds like a special interface that may have been fitted to a printer for use in a mainframe environment. The Centronics 702 and 703 had a slot in the back where a serial interface card could be plugged in. Later versions had a serial interface on the main PCB. The same plug in interface card was used in the Centronics 101, and I suspect other models as well. Your description suggests a special OEM interface plugged into this same slot. >The PC LPT is really crappy in comparison...! Not really >Also, IIRC BIOS/reserved adress range support four LPT, but >MS-DOS and Windows only 3, I don´t know how about other PC OS:es. This address reservation was peculiar to the IBM (and clone) BIOS's. While there were four address slots available, only three addresses were ever used, as outlined in previous mails. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body

>> Exactly, and that is what was on the monochrome card. To be pedantic the >> base address of the port on the monochrome card was at 3C8 (IIRC) and the >Well I did put IIRC :))) You did, but you put "pedantic" in the same sentence :-o -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body