TERMINATION ARRANGEMENT AT AN INTERFACE AT ONE END OF THE CONNECTABLE AND DISCONNECTABLE MULTI-CONDUCTOR CABLE

Abstract: The invention relates to an arrangement at an interface at one end of a connectable and a disconnectable multi-conductor cable (120). The arrangement comprises a first multi-contact member (10; 226) and a second multi-contact member (80), which is connectable to the first multi-contact member. The first multi-contact member (10; 226) comprises a plurality of contact elements (20, 50), some (20) of which at least are coupled to a data bus (40, 230), for example a so-called SCSI bus, which requires terminator means (70) coupled to each of the bus conductors, when the multi-conductor cable is disconnected, but not when it is connected. The arrangement also comprises a sensor means (50, 55, 90; 270, 280, 300) for sensing whether the multi-conductor cable is connected or disconnected, and a switch means (60; 250) controlled by the sensor means (50, 55, 90; 270, 280, 300) and comprising a switch element (62) coupled between each bus conductor and its associated terminator means (70). The sensor means (50, 55, 90; 270, 280, 300) is arranged to control the switch means (60) to keep the switch element (62) closed when the multi-conductor cable is disconnected and open when the multi-conductor cable is connected.

Description: Termination Arrangement at an Interface at One End of the Connectable and Disconnectable Multi-Conductor Cable The present invention relates to an arrangement of the type described in the preamble to claim 1. The Background of the Invention For data transmission in small-sized computer systems, SCSI (Small Computer System Interfaces) are often used. It is then possible to couple an SCSI-bus to a plurality of units. SCSI units can be coupled together in several stages, or be coupled in series. SCSI units can be coupled together by a cable e.g. comprising 50 conductors. Alternatively, the SCSI units can be coupled together with a cable with approximately 68 conductors. Both ends of the cable, or the SCSI bus, are terminated with termination means for several reasons, among them to prevent noise by providing a high signal/noise ratio and maintaining the SCSI bus in a known state. An important purpose of the SCSI termination is adaptation of the characteristic impedan- ce of the transmission conductors and attenuation of signal reflections. According to known technology an SCSI bus is terminated by connection to an external device with terminal resistors or each contact member in the connector for external SCSI units. An SCSI bus must be terminated with termination means at both ends. This is usually done by a resistor net, for example mounted in a DEP base at each end of the SCSI bus. According to an alternative known solution, a device is arranged with termination resistors internally on a circuit board in the computer unit. In order to engage or disengage the termination resistors, the computer unit must be opened and the termination means with termination resistors must be pressed manually into a socket or be pulled out of this socket. The solutions have the disadvantage that the termina- tion means is a separate unit which must be operated separat¬ ely. According to another known solution, described in the US-A-4 988,890 a plurality of units are connected by allowing the multi-conductor cable or SCSI bus to run in a circular circuit or loop, from the first unit to the other and back to the first unit again. Both of the termination means are in the first unit. This has the obvious disadvantage that two expensive multi-conductor cables must be coupled to the first unit and to the other units. One variant of this solution with the circular circuit is described in US-A-5 099 137. These previously known designs thus require extra work from an operator who wishes to couple together different external SCSI units and extra links of cable which must be coupled and installed. The purpose of the present invention The primer purpose of the present invention is to simplify and automate the connection of external units via SCSI inter¬ faces. Another purpose of the present invention is to provide automatic connection and disconnection of termination means for a first SCSI unit in a first computer unit depending on whether an external SCSI unit has been connected to or dis¬ connected from the first computer unit. The primary purpose is achieved with an arrangement of the type which is described in the characterizing clause of claim 1. Further features and further developments of the arrangements according to the invention are disclosed in the rest of the patent claims. Short description of the drawings For simple understanding and execution of the present inven¬ tion, it will be described by means of examples with referen- ce to the accompaning drawings, in which: Fig.l shows a schematic representation of one embodiment of the device according to the invention. Fig.2 shows a block diagram of an arrangement according to the invention. Fig.3 shows a connection of multi-contact members and the coupling together of computer units according to one em- bodiment of the present invention. Fig.4 shows one embodiment of a device according to the invention. Detailed description of the invention The invention will be described here with reference to Fig.l. According to one embodiment, the arrangement according to the invention comprises a first multi-contact member 10. The first multi-contact-member 10 comprises first contact members 20, which are individually connected to conductors 30 in a first multi-conductor cable 40. Some of the conductors, or all of the conductors, in the multi-conductor cable 40 can make up a data bus, such as an SCSI bus. The first multi-contact member 10, also comprises at least one first control signal contact member 50, which is con¬ nected via a conductor 55 to a switch means 60 comprising a control element 61 which controls a number of normally closed switching elements 62. A switching element 62 can e.g. con¬ sist of some sort of semiconductor valve device. Depending on the signal level at the control signal contact member 50, the switch means 60 will connect or disconnect the termination or terminator means 70. The signal level at the control signal contact member 50 is preferably a voltage level, but as an alternative it can be a current level for example. Each terminator means 70 is coupled by a contact element 62, controlled by the switch means 60, to individual first con¬ tact members 20 in the first multi-contact member 10, and thus also to conductors 30 in the first multi-conductor cable 40. It is also within the scope of the invention that the multi- conductor cable 40 comprises one or more conductors which are not coupled to any terminator means 70. The multi-conductor cable 40 can, for example, comprise one or a pair of con¬ ductors for power supply or earth conductors. Said conductors need not be coupled to terminator means, as is known by the person skilled in the art. The terminator means 70 can comprise one or more resistors and/or other passive circuit elements. The terminator means 70 can alternatively comprise active circuit elements, such as integrated circuits, possibly in combination with passive circuit elements. The first multi-conductor cable 40 is shown in Fig.l with only two conductors to simplify the description, but in reality the number of conductors can be higher. The cable 40, for example, can comprise 18 conductors and the first multi- contact member can comprise 18 first contact elements 20 and the first control signal contact element 50 which sends a signal to the control device 61 to move all of the switch elements 62 in unison, or the plurality of first control signal contact elements 50, which signal a plurality of control devices 61 to each control in the individual group of switch element 62. The arrangement also comprises a second multi-contact member 80 which can be coupled to the first multi-contact member 10. When the second multi-contact member 80 is not connected to the first contact member 10, there is no control signal from the control signal contact element(s) 50 to the control device 61 to control the switch element 62. Then the switch means 60 will keep the connection closed between each con¬ ductor 30 and the cable 40 and the respective terminator means 70. At that end of the multi-conductor cable 40, the conductors 30 are thus terminated so that signal reflections and other problems do not arise. The other end 75 of the multi-conductor cable 40 can also be terminated by some sort of additional termination or ter¬ minator means. The other end 75 can also be coupled to a device, such as a processor or personal computer. The multi- conductor cable 40 can also be terminated at both ends, i.e. by the terminator means 70 at one end and by the additional terminator means at the other end. To make sure that the switch means 60 keeps the switch ele- ment 62 closed when the second multi-contact member 80 is not coupled to the first multi-contact member 10, a high signal level is placed on the conductor 65, for example by a so- called "pull-up" resistor 90. The resistor 90 is connected between the first multi-voltage level U. and the conductor 55, and thus causes the signal level in the conductor 55 to be high when the first control signal element 50 is not connected to any other contact element with another signal level. When the signal level in the conductor 55 is high, the switch means 60 will keep its switch element 62 in a closed state, which connects the conductors 30 to the terminator means 70. When the second multi-contact member 80 is connected to the first multi-contact member 10 the first control signal element 50 is connected to the second control signal element 10 in the second multi-contact member 80. The second control signal element 100 can be coupled, via a conductor 110 in a multi-conductor cable 120, for example, to a second voltage level U- (Fig.l, Fig.2). The second voltage level U Q can, for example, be a low voltage level such as signal ground. When the second multi-contact member 80 is connected to the first multi-contact member 10, the signal level in the conductor 55 will agree with the signal level U_, and the switch means 60 will change the state to keep its switch element 62 in the open state. The terminator means 70 are thus disconnected from the conductors 30 in the multi-conductor cable 40. The arrangement according to the invention thus means that a sensor causes the terminator means 70 to be decoupled from the signal conductors 30, at the same time as second contact elements 130 of the second multi-contact member 80 are coup¬ led to the first contact elements 20 of the first multi- contact member 10. The second contact elements 130 are indi- vidually connected to conductors 140 in the multi-conductor or signal cable 120. The first multi-contact member 10, the first cable 40 or the first bus 40, the terminator means 70 and the switch means 60 are comprised in the first computer unit 150. The multi- conductor cable 120 consists preferably of an external SCSI- bus which connects the first computer unit 150 with a second computer unit 160. Fig.2 shows how the first computer unit 150 can be coupled to the second computer unit 160 and to a third computer unit 170. The first multi-contact member 10 of the first computer unit 150 can be coupled to a third multi-contact member 180 via the second multi-contact member 80 and the multi-conductor cable 120. According to one embodiment, the third multi- contact member 180 couples the conductor 110 of the multi- conductor cable 120 to the signal level U Q via a fourth multi-contact member 200 in the second computer unit 160. The signal level U Q is supplied according to this embodiment by the second computer unit 160. According to another embodiment, the second voltage level U_ is supplied to the first control signal element from a source within the first computer unit, as shown in Fig.3. According to the embodiment shown i Fig.3, the first computer unit 150B comprises a first multi-contact member 10B. The first multi- contact member 10B comprises, as does the previously describ¬ ed multi-contact member 10, first contact elements 20B and the first control signal contact element 50B, but it also comprises a third control signal contact element 202 which is connected to the second signal level U_ within the first computer unit 15OB. When a second multi-contact member 8OB is coupled to the first multi-contact member 10B, the first control signal contact member 50B is coupled to the third control signal contact member 202, via corresponding contact elements 204 and 100B in the multi-contact member 80B. The contact elements 204 and 100B can be directly joined to each other via a conductor 206 in the multi-contact member 80B as shown in Fig.3. Alternatively, the multi-contact member 80B is not provided with any conductor 206 and the two contact elements 204 and 100B can then be joined to each other via conductors 208 and HOB which are included in a multi-con¬ ductor cable 120B and which are joined to each other at or within the second computer unit 160B at the opposite end of the multi-conductor cable 120B. Both conductors HOB and 208 can be connected to the signal level U_ in the second com¬ puter unit 160B as well, as shown in Fig.3. The multi-conduc¬ tor cable 120B can correspond in other respects to the multi- conductor cable 120 described above and below. Fig.2 shows signal conductors 140 in the multi-conductor cable 120 coupled via the multi contact member 180 and the multi-contact member 200 to a unit 220 in the second computer unit 160. The unit 220 can comprise an SCSI control unit, and other data processing equipment included in the second co - puter unit 160. According to another embodiment of the invention, the multi- conductor cable 120 is securely connected to a second com- puter unit 160, instead of using third and fourth multi- contact members 180 and 200. Within the second computer unit 160, the bus conductors 140 can be joined to bus conductors 30'. The second computer unit 160 can comprise terminator means 70' corresponding to the terminator means 70 in the first computer unit 150. Further¬ more, the computer unit 160 can comprise a switch means 60' and a multi-contact member 10' corresponding to the switch means 60 and the multi-contact member 10 in the first com¬ puter unit 150. This means that further computer units can be daisy-chained into the computer units 150 och 160, with automatic connec- tion or disconnection of the internal terminator means 70 or 70' respectively. Fig.2 shows an example where two computer units 160 and 170 are daisy-chained to the first computer unit 150. The third computer unit 170 is, in the configuration shown in Fig.2, coupled to the second computer unit 160 via a multi- conductor cable 120', corresponding to the multi-conductor cable 120 between the computer units 150 and 160. As regards the connection and the interface to other units, the third computer unit 170 corresponds to the second com¬ puter unit 160. Thus the third computer unit 170 comprises bus conductors 30'', corresponding to the bus conductors 30' and the computer unit 160, and means 70'' and 60'' and a multi-contact member 10'' corresponding to the above describ¬ ed means 70', 60' and 10' respectively. The unit 220' and the third computer unit 170 can correspond to the unit 220 in the second computer unit 160, but the data processing equipment can be of different types, as will be understood in the following detailed discussion of the peripheral equipment. Since the third computer unit 170 is connected to the second computer unit 160, the switch means 60' of the second comput- er unit 160 will be in its open state. The terminator means 70' thus do not couple to the bus conductors 30'. No additional computer unit is connected, however, to the multi-contact member 10'' of the third computer unit in the configuration shown in Fig.2. This means that the terminator means 70'' are coupled to the bus conductors 30'' in the manner described above with reference to Fig.l, and the bus consisting of the signal conductors 30'' is thus terminated with the " terminator means 70''. Thus the SCSI-bus can be terminated, firstly, at the end 75 (Fig.l) of the bus with the aid of the additional terminator means, as was mentioned above, and, secondly, by the terminator means 70'' at the opposite end of the SCSI-bus. The arrangement according to the invention makes possible easy daisy-chaining of a number (n) of computer units and the internal means are automatically engaged in the computer unit where bus termination is required, whereas the terminator means are automatically disconnected in the computer units when they are not needed. The arrangement according to the invention thus relates to interfaces, preferably small Computer Systems Interfaces (SCSI.s) , for coupling to one or more peripheral units to a computer. The computer can, for example, be a personal com¬ puter, and the peripheral units can, for example, be disc drives, tape store units or CD-ROM units. According to one application of the arrangement according to the invention, the first computer unit 150 consists of a personal computer with external SCSI interfaces and the second computer unit 160 consists of a disc storage unit, when the third computer unit 170 consists of a tape storage unit. An operator wishes, however, to connect the tape stor¬ age unit 170 to a disc storage unit 160 to make a back-up copy of the contents of the disc storage unit. Where interfaces and busses according to the prior art are used, the operator must manually open the cover in which the terminator means are disposed and disconnect the terminator means at the disc storage unit when the tape storage unit 170 is connected to the disc storage unit 160. When the operator again wishes to disconnect the tape storage unit 170 from the disc storage unit 160, the cover must again be opened and the terminator means be engaged manually again. If the known technology with ring-coupling is used, this presents problems because the operator must break the loop and arrange at least two multi-conductor cables. With the arrangement according to the invention, however, the operator does not need to concern himself with the terminator means. When the operator connects the tape storage unit 170 to a disc storage unit 160 with an interface arrangement according to the invention, the internal bus terminator means 170' are automatically disengaged. Only one multi-conductor cable is needed, namely the multi-conductor cable 120'. Fig.4 shows one embodiment of a computer unit 222 with the inventive arrangement. The computer unit 222 comprises an SCSI control unit 224, which can comprise, for example, the circuit MB 86 601 manufactured by Fujitsu. Similar circuits are manufactured by NCR et al. The SCSI control unit 224 is joined to a multi-contact member 226 for connecting external SCSI units. The connection between the SCSI control unit 224 and the multi-contact member 226 can consist of an internal bus 230 comprising a plurality of signal conductors. The internal bus 230 can also comprise two sub-busses 232, 234, of which the first sub-bus 232 can comprise a number of data conductors and the second sub-bus 234 can comprise a number of control signal conduc- tors. The internal bus 230 can also be coupled to a multi- contact member 240 for connecting a first SCSI unit internal¬ ly in the computer unit 222. The multi-contact member 240 can, in accordance with one embodiment, correspond to the previously described fourth multi-contact member 200, in a configuration where the second computer unit 160 in Fig.2 is the computer unit 222 shown in Fig.4. Thus the multi-contact member 240 can be used to connect the computer unit 222 with other computer units. The multi-contact member 240 comprises, according to said em¬ bodiment, at least one contact element 241 which is coupled to the second signal level U_. The multi-contact member 240 also comprises a plurality of contact elements 242. The function of these contact elements 242 is well know to the person skilled in the art, and there¬ fore they will not be described in more detail. The internal bus 230 is also coupled to input terminals 245 of a controllable SCSI terminator means 250. The controllable SCSI terminator means 250 can consist of an integrated cir¬ cuit, such as the UC5601 which is manufactured by Unitrode. The controllable SCSI terminator means 250 is disposed, depending on a control signal to a control input terminal 260, to either connect the terminals 245 with the terminator means or break said connections. The multi-contact member 226 comprises a plurality of contact elements 262. The normal functioning of these contact elements is well known to the persons skilled in the art and therefore no detailed description is required here. One contact element has, however, a function which is distinctive to the present invention. The control signal to the control in-put terminal 260 is dependent on the signal level at a control contact element 270 of the multi-contact member 226. The multi-contact member 226 is not connected to any external SCSI unit, the signal level at the control contact element 270 is caused to maintain a high level with the aid of a resistor 280, the first connection of which is coupled to a first signal level U. and the second connection of which is connected to the contact element 270 via the conductor 290. The signal level U- is preferably a voltage of + 5 volts, but it can also be some other suitable signal level. The second connection of the resistor 280 is also connected to the in-put terminals of an invertor 300. The out-put of the invertor 300 is connected to the control in-put terminal 260 of the controllable SCSI terminator means 250. When the signal level at the contact element 270 is high, this causes the signal of the invertor means 300 to the control in-put terminal 260 to be low, and the controllable SCSI terminator means 250 will thus engage the terminator resistances. Conversely, when external SCSI unit is connected to the multi-contact member 226 the control contact element 270 will contact a contact element with the second signal level U 0 . This causes the control contact element 270 to assume a signal level U_. The signal level U_ is preferably a voltage level of zero volts or signal ground. When the control con¬ tact element 270 has a signal level U Q of zero volts, this causes the invertor 300 to place the high signal level at the control in-put terminal 260. The controllable SCSI terminator means 250 will thus disconnect the terminator resistances. The multi-contact member 226, which is shown in Fig.4, can in accordance with one embodiment correspond to the previously described multi-contact member 10B in Fig.3. The multi- con¬ tact member 226 comprises, in accordance with this embodi¬ ment, at least one contact element 310 which is connected to the signal level U_. The invention makes it much simplier for the operator to connect external SCSI units, and only one multi-conductor cable 120' is required when an additional external unit 170 is to be daisy-chained to the already connected units 150 and 160, as is shown in Fig.2. Computer units equipped with the arrangement according to the invention are also compatible with other standard computer units known in the art. If the signal level U_ is set at signal ground, the control contact element 50, 270 will be imparted the signal level U Q even with multi-contact members of the prior art. This means that if, for example, a periphe¬ ral unit of the prior art is connected to the computer 170 in Fig.2, the terminator means 70" will be disconnected.

Claims: Claims 1. Arrangement at an interface at one end of a connectable and disconnectable multi-conductor cable (120) , said arran¬ gement comprising: a first multi-contact member (10;226) and a second multi-contact member (80) which is connectable to the first multi-contact member, said first multi-contact member (10;226) comprising a plurality of contact elements (20,50) of which at least some of the contact elements (20) are coupled to a data bus (40,230), for example, a so-called SCSI-bus, which requires terminator means (70) coupled to each of the conductors of the bus, when the multi-conductor cable is disconnected, but not when it is connected, charac- terized by a sensor means (50,55,90;270,280,300) for sensing whether the multi-conductor cable is connected or disconnected, and a switch means (60;250) controlled by the sensor means (50,55,90;270,280,300) , comprising a switch element (62) coupled between each bus conductor and its associated ter¬ minator means (70), said sensor means (50,55,90;270,280,300) being arranged to control the switch means (60) to keep the switch element (62) closed when the multi-conductor cable is disconnected and open when the multi-conductor cable is connected. 2. Arrangement according to claim 1, characterized in that the sensor means comprise at least one control contact element (50,270) dedicated for sensing in the first multi- contact member (10,226) and control signal source U Q coupled to a contact element (100) in the second multi-contact member (80) and which can be coupled to the control contact element (50,270), said control signal source providing such a control signal that the switch means (60,250) is made to keep the switch element (62) open. 3. Arrangement according to Claim 2, characterized in that the swich means (60;250) connects the terminator means (70;250) to the data bus (40;230) when the signal level at the control contact element has a first value (U) , and that the switch means (60;250) disconnects the terminator means (70;250) from the data bus (40;230) when the signal level at the control contact element has a second value U Q . 4. Arrangement according to Claim 3, characterized in that the signal level at the control contact element (50) is made to assume the second value (U Q . when the multi-contact member (80) is coupled to the first multi-contact member (10) ; and that the signal level at the control contact element (50) is made to assume the first value (U) when the second multi- contact member (80) is not coupled to the first multi-contact member (10;226) . 5. Arrangement according to Claim 4, characterized in that the first value and the second value are different voltage levels. 6. Arrangement according to Claim 1 or 2, characterized in that the first multi-contact member (10,226), the data bus (40,230), the switch means (60;250) and the terminator means (70,250) are included in a first computer unit (150); and that the second multi-contact member (80) is joined via the multi-condutor cable (120) to a second computer unit (160) , which includes the control signal source (U Q ) . 7. Arrangement according to Claim 6, characterized in that the first computer unit consists of a data processing unit (150) and the second computer unit consists of a peripheral unit (160) . 8. Arrangement according to Claim 6, characterized in that the first computer unit consists of a peripheral unit (160) and the second computer unit consists of an additional perip¬ heral unit (170) .

Inventors: HOEGLUND ANDERS, HOEGLUND, ANDERS
Applicants: HOEGLUND ANDERS, ICL SYSTEMS AB
Application year: 1993
Main classification: H04L12
IPC codes: G06F13, H01R13, H04L12, H04L29