.
`
`Umted States Patent [19]
`Patton
`I
`
`llllllllllllllllllllll'lllllllllllllllllllllllllllllllllllllllllllllllllllll
`[11] Patent Number:
`5,121,482
`[45] Date of Patent:
`Jun. 9, 1992
`
`USOO512l482A
`
`[54] CIRCUIT AND METHOD FOR AUTOAlATIC
`'
`INPULOUTPUT CONFIGURATION
`THROUGH LOCAL AREA NETWORK
`_ ~
`DETECTION
`
`[75] Inventor: David B. Patton, Vancouver, Wash.
`_
`[73] Assignee: Hewlett-Packard Company, Palo
`Alto, Calif.
`
`[21] Appl. No.: 405,496
`_
`[22] Filed:
`
`Sep. 11, 1989
`
`Int. 0-5 ..................... ..
`[52] US. Cl. .................................. .. 395/275; 324/656;
`324/712; 324/713; 340/ 6150; 340/664;
`364/242-95; 364/927-96
`
`of Search .............. .
`364/900, 927-961 307/362; 324/705, 713, 98’ 99
`R, 656, 691, 712.- 118, 120; 340/660, 661.- 664;
`371/215
`
`[56]
`
`References Cited
`US. PATENT DOCUMENTS
`3.978.402 8/1976 Ryder ........................... .. 324/713 X
`
`4.008.405 2/1977 Neumann et al. ................. ,. 307/231
`4.041.288 8/1977 Conway et al. . . . , .
`. . . .. 324/99 R X
`4.575.714 3/1986 Rummel ............ ..
`324/691 X
`4.644.194 2/1987 Birrittella et al.
`307/362 X
`4.647.912 3/1987 Bates et al. . . . . . . . . . .
`. . . .. 340/8255
`
`307/362 X
`4,841,177 6/1989 Sugiyama 61 al
`4,983,858 l/l99l lshikawa ........................... .. 307/362
`
`Primary Examiner-Michael R. Fleming
`Assistant Examiner—Glenn A. Auve
`
`ABSTRACT
`[57]
`,
`I
`_
`_
`,
`The invented circuit lncludes an I/O driver capable of
`current to an
`connector, 3 current detec
`“on circuit that may include a Curl-em limit resistor and
`a differential ampli?er, a comparator to compare the
`level of current to a predetermined level and to produce
`an output Signal based thereonY and a translator to con.
`vert the output signal from the comparator into a tran
`sistor-transistor logic signal. The device that includes
`the invented circuit then interprets the logic signal as
`identifying either a serial I/O system or a LAN I/O
`system.
`
`9 Claims, 2 Drawing Sheets
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`U.S. Patent
`
`June 9, 1992
`
`Sheet 1 of 2
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`I
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`MP
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`O \ H
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`U.S. Patent
`
`June 9, 1992
`
`Sheet 2 of 2
`
`5,121,482
`
`30
`
`42\
`
`ENABLE DRIVER
`
`WAIT
`
`44
`J
`
`NO
`
`46
`
`YES
`
`481
`RUN IN SERIAL MODE
`
`/51
`RUN IN LAN MODE
`
`FIG.2
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`5,121,482
`2
`transistor-transistor logic signal. The device that in
`cludes the invented circuit then interprets the logic
`signal as identifying either a serial l/O system or a LAN
`I/O system.
`
`1
`
`CIRCUIT AND METHOD FOR AUTOMATIC
`INPUT-OUTPUT CONFIGURATION THROUGH
`LOCAL AREA NETWORK DETECTION
`
`TECHNICAL FIELD
`This invention relates to a device that may operate in
`either a serial input-output system or a local area net
`work input-output system. More particularly, this in
`vention relates to a device that automatically detects
`whether it is part of a serial input-output system or a
`local area network input-output system.
`
`20
`
`BACKGROUND ART
`A device such as a computer printer is connected to
`a host computer by a cable. The cable is attached at one
`end to a port on the printer and at the other end to a
`port on the computer. Both the printer and the host
`computer have input-output (“I/O”) drivers to receive
`and transmit signals through the cable.
`When a single printer serves a single computer in a
`stand-alone system, the signals received and transmitted
`between them are often asynchronous, transmitted seri
`ally in time and transmitted only on one channel. That
`type of U0 is commonly known as serial I/O.
`Alternatively, a single printer may be part of a local
`area network (“LAN") and service several computers.
`A LAN is simply a group of interconnected devices or
`nodes. Devices operating in a LAN typically transmit
`30
`and receive data between themselves by using LAN
`I/Os. LAN l/Os operate with synchronous communi
`cation and data transmission that is different and much
`faster than the transmission used by serial I/O systems.
`To be able to use a device such as a printer on both a
`serial l/O system and a LAN I/O system, the device
`must be able to distinguish between the systems because
`of the different data transmission characteristics. This
`has been accomplished in previously existing devices by
`using a mode switch to toggle between serial and LAN
`modes. Thus, to use a printer on a LAN, the user would
`have to con?gure the system by manually setting a
`switch. This usually involves remembering that the
`system needs to be con?gured, referring to a manual,
`?nding the switch on the device, determining whether
`it needs to be changed and if so, changing it. Often the
`product has to be dismantled to some extent to access
`the switch. If the user changes back to a serial I/O
`system, the switch would need to be changed back.
`The invented "Circuit and Method for Automatic
`Input-Output Con?guration Through Local Area Net
`work Detection" automatically recognizes whether the
`device is part of a serial I/O system or a LAN l/O
`system and con?gures the device accordingly. The user
`does not have to set any switches or remember to con
`?gure the system. Additionally, the cost of the compo
`nents in the invented circuit is less than the cost of a
`suitable switch to perform the same function. The in
`vented circuit will allow a device to detect whether it is
`plugged onto a serial I/O system or a LAN l/O system.
`
`35
`
`45
`
`50
`
`55
`
`DISCLOSURE OF THE INVENTION
`The invented circuit includes an I/O driver capable
`of supplying current to an I/O connector, a current
`detection circuit that may include a current limit resis~
`tor and a differential ampli?er, a comparator to com
`pare the level of current to a predetermined level and to
`produce an output signal based thereon, and a translator
`to convert the output signal from the comparator into a
`
`65
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a schematic diagram of a preferred embodi
`ment of the invented circuit.
`FIG. 2 is a simple block diagram showing the steps of
`the invented method.
`
`DETAILED DESCRIPTION AND BEST MODE
`FOR CARRYING OUT THE INVENTION
`FIG. 1 shows generally at 11 a circuit constructed
`according to the invention. Circuit 11 may be employed
`in a printer, modem or any device that may operate in
`either a serial I/O system or a LAN I/O system. Circuit
`11 includes an I/O connector 13 to connect with other
`devices. Connector 13 may simply be the port on a
`printer that receives a cable connected to a computer,
`and may be referred to as I/O connector means.
`Circuit 11 also includes a driver means, including an
`I/O driver 14 that supplies the signals to connector 13
`that are to be transmitted to connected devices. In FIG.
`1, driver 14 is a 26LS3O integrated circuit. The standard
`symbols explaining the driver are shown in the drawing
`to facilitate understanding but need not be discussed to
`understand the invention.
`Between connector 13 and driver 14 is a current
`detection circuit including a ?rst current limit resistor
`16 and a second resistor 18. These resistors create a
`voltage drop between driver 14 and connector 13. In
`the preferred embodiment, resistors 16 and 18 each have
`a resistance of 24-ohms, as shown in the schematic.
`When driver 14 is enabled, it may send an output
`signal or current to connector 13 across resistor 16. The
`current through resistor 16 is measured by differential
`ampli?er 20. The output of ampli?er 20 is compared
`with a reference signal by a comparator means includ
`ing a comparator 22 and then translated into a transis
`tor-transistor logic (“TTL”) signal 26 by a translator
`means including a translator 25. The translator means
`may also be referred to as TTL circuitry. In the pre
`ferred embodiment, translator 24 is an LM339 inte
`grated circuit. The TTL signal can then be fed into a
`logic input and interpreted to identify either a serial I/O
`system or a LAN I/O system.
`FIG. 1 depicts a preferred embodiment of the in
`vented circuit and shows the values of the circuit’s
`components. The speci?c components are familiar to a '
`person skilled in the art of electric current detection and
`therefore are not discussed in detail. Other values may
`also be used for the components shown in FIG. 1. In
`fact, numerous other current detection circuits may be
`used to determine the current from the driver to the
`connector. Such current detection circuits may also be
`referred to as detection means.
`The invented circuit works because a serial l/O con
`nection to connector 13 has different properties than a
`LAN I/O connection. A direct serial I/O connection
`has a high impedance and therefore results in a, low
`current across resistor 16 when driver 14 is enabled. In
`the preferred embodiment, the current across resistor 16
`generally does not exceed 3.25-mA when connector 13
`is connected to a serial I/O system.
`A LAN l/O connection has a low impedance because
`it includes a transformer and therefore, a high current
`
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`5,121,482
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`3
`and large voltage drop results across resistor 16 when
`driver 14 is enabled. In the preferred embodiment. the
`current across resistor 16 is generally 30-mA to 40-mA
`when connector 13 is connected to a LAN I/O system.
`As explained, the current across resistor 16 changes
`depending on whether connector 13 is connected to a
`serial I/O or a LAN l/O. Ampli?er 20 detects the cur
`rent and outputs a signal to comparator 22, which then
`compares it with a predetermined reference level. If the
`reference level is met, translator 25 outputs a TTL sig
`nal that identi?es the type of I/O system. For example,
`if connector 13 is connected to a serial l/O, then the
`current across resistor 16 is low and signal 26 is low or
`zero. If connector 13 is connected to a LAN I/O, then
`the current across resistor 16 is high and signal 26 is
`high or one.
`
`OPERATION
`The steps that are taken by circuit 11 are illustrated in
`FIG. 2 by a block diagram shown generally at 40. Ini
`tially, driver 14 is enabled at step 42, usually by simply
`turning on the device that includes circuit 11 and sup
`plying power to the driver. The invented method waits
`at step 44 before detecting current across resistor 16 in
`order to let the circuit settle. Typically, the method
`waits SO-us to lOO-us.
`As represented by step 46, the method then measures
`the current, determines whether it is high or low across
`resistor 16 and generates the appropriate TTL signal,
`which may also be referred to as the LAN bit. If the
`current is low across resistor 16, then the method does
`not generate a LAN bit and the device identi?es a serial
`l/O system and runs in serial mode, as shown by step 48.
`If the current is high across resistor 16, then the method
`does generate a LAN bit and the device identi?es a
`LAN l/O system and runs in LAN mode, as shown by
`step 51.
`
`35
`
`INDUSTRIAL APPLICABILITY
`The invented circuit and method are applicable to
`any device that may operate in either a serial I/O sys
`tem or a LAN I/O system. Speci?cally, the invented
`circuit and method are applicable to printers, modems,
`computers, and other similar devices. While the best
`mode and preferred embodiment of the invention have
`been disclosed, changes may be made without departing
`from the scope of the invention.
`What is claimed is:
`1. Apparatus capable of differentiating between a
`connected serial input-output (SERIO) system and a
`connected local area network input-output (LANIO)
`system, said apparatus comprising:
`an input-output connector adapted for connection
`selectively to such a SERIO or LANIO system;
`driver means operatively connected to said connector
`for supplying a signal to the connector and by way
`of said connector to a connected system under
`circumstances where the connector is connected to
`a SERIO or LANIO system; and
`detection means operatively connected to with said
`connector for measuring the level of a signal sup
`plied from said driver means through said connec
`tor to a connected system to determine whether the
`signal meets a predetermined level which is inter
`pretable to differentiate between a connected serial
`
`40
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`45
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`55
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`65
`
`4
`input-output system and a connected local area
`network input-output system.
`2. The apparatus of claim 1. wherein said detection
`means includes translator means for identifying a serial
`input-output system when the signals level does not
`meet the predetermined level, and for identifying a local
`area network system when the signals level meets the
`predetermined level.
`3. The apparatus of claim 1, wherein the signal is
`electric current, and said detection means includes a
`current limit resistor through which such current flows
`and a differential ampli?er operatively connected to
`said resistor to measure the current through the resistor.
`4. The apparatus of claim 3, wherein said differential
`ampli?er produces an output signal, and said detection
`means further includes a comparator that compares the
`output signal of the differential ampli?er with a prede
`termined level to produce a comparator voltage.
`5. The apparatus of claim 4, wherein said detection
`means includes a translator that converts the compara
`tor voltage alternatively into high and low transistor
`transistor logic levels.
`6. The apparatus of claim 5, wherein said translator
`identi?es a serial input-output system when the logic
`level is low, and identi?es a local area network input
`output system when the logic level is high.
`7. A printer capable of differentiating between a con
`nected serial input-output (SERIO) system and a con
`nected local area network input-output (LANIO) sys
`tem, said printer comprising:
`an input-output connector on the printer adapted for
`connection selectively to such a SERIO or
`LANIO system;
`an input-output driver operatively connected to said
`connector and capable of supplying current in dif
`ferent levels to said connector and by way of said
`connector to a connected SERIO or LANIO sys
`tem;
`detection means operatively connected to said driver
`for detecting the level of current therefrom sup
`plied through said connector to a connected sys
`tem; and
`comparator means operatively connected to said de~
`tection means for comparing the level of any de
`tected current with a predetermined level.
`8. The printer of claim 7, further comprising transla
`tor means for causing the printer to identify a serial
`input-output system when the currents level does not
`meet the predetermined level, and to identify a local
`area network system when the current’s level meets the
`predetermined level.
`9. A method whereby a device having an input-out
`put connector and an operatively connected input-out
`put driver capable of supplying current to the connec
`tor may differentiate between a connected serial input
`output system and a connected local area network in
`put-output system, said method comprising:
`enabling the input-output driver and thereby supply
`ing current to the connector, and by way of said
`connector to a connected system;
`measuring current supplied from the driver to and
`through the connector; and
`determining whether the supplied current is of a pre
`determined level, and if not, identifying a serial
`input-output system, but if so, identifying a local
`area network input-output system.
`it
`t
`*
`*
`$
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