MULTICONFIGURABLE INTERFACE CIRCUIT

Abstract: Interface circuit of simple construction which is suitable for use with either a short (less than 15 metres) or a long (15 to 50 metres) input/output cable (30, 31). The interface circuit includes a plurality of differential line drivers (38), and connection means (35, 37, J5) for selectively adapting electrical network means included in the interface circuit so as to make each driver (38) selectively compatible with either a short input/ouput cable or a long input/output cable. Each driver (38) has a first output which is permanently connected to a respective conductor (30) of the input/output cable, and a second output which is connectable via jumper means (J5) to a respective conductor (31) of the input/ouput cable if the cable is long. If the cable is short, the relevant conductor is connected to ground via further jumper means.

Description: MULTICONFIGURAB E INTERFACE CIRCUIT Technical Field The present invention relates to interface circuits for use with peripheral devices, such as printers, in computer systems. Background Art In many computer systems, a host processor is provided having a peripheral port for providing data bits in a serial format. A peripheral adapter is provided for performing a serial-to-parallel conversion of the data bits, for buffering the data bits, and for providing handshaking between the host processor and the computer printer. In such a computer system, the peripheral adapter typically includes an interface circuit having drivers for driving data conductors in an input/output cable between the periph-e_ra J _ad.apter and the printer, and receivers for receiving various status and handshaking data bits from the printer. Because of the resistance and distributed capacitance of the conductors in the input/output cable, the designs of the drivers and receivers in the interface circuit of the peripheral adapter, and a corresponding interface circuit in the printer, are dependent on the length of the input/output cable. Typically, if the length of the input/output cable is less than about 15 metres long, the drivers and receivers in the interface circuits are single ended. If, however, the input/output cable is between about 15 metres and 150 metres long, the drivers and receivers in the interface circuits are designed using differential amplifiers. In the past, separate interface circuits have been provided on removable boards in a peripheral adapter and printer. If the input/output cable was less than 15 metres long, a separate short line interface circuit board was installed in both the peripheral adapter and the printer. If the input/output cable was between 15 metres and 150 metres long, a separate long line interface circuit board was installed in both the peripheral adapter and the printer. Disclosure of the Invention It is an object of the present invention to provide an interface circuit which is of simple construction and which is suitable for use with a short or a long input/output cable. According to the invention there is provided an interface circuit for use with a computer input/output cable connected to a computer peripheral device including a plurality of drivers each having input means for receiving data bits, and output means for driving conductor means in the input/output cable, characterized by electrical network means adaptable for making each of said drivers compatible with a first predetermined length of input/output cable or with a second predetermined length of input/output cable, and connection means for selectively adapting said electrical network means so that said drivers are selectively made compatible with either said first predetermined length or said second predetermined length of input/output cable. Brief Description of the Drawings Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a block diagram of a computer system in which an interface circuit in accordance with the present invention may be used; Fig. 2 is a schematic diagram of a prior art short line interface adapter; Fig. 3 is a schematic diagram of a prior art long line interface adapter; Fig. 4 is a schematic diagram of a system including a driver of the present interface circuit configured as a short line driver; Fig. 5 is a schematic diagram of a system including a driver of the present interface circuit configured as a long line driver; Fig. 6 is a schematic diagram of a system including a receiver of the present interface circuit configured as a short line receiver; Fig. 7 is a schematic diagram of a system including a receiver of the present interface circuit configured as a long line receiver; Figs. 8A and 8B, arranged as shown in Fig. 9, form a schematic diagram of drivers of the present interface circuit for use in a peripheral adapter; and Figs. 10A, 10B and IOC, arranged as shown in Fig. 11, form a schematic diagram of receivers of the present interface circuit for use in a peripheral adapter. Best Mode for Carrying Out the Invention Fig. 1 is a block diagram of a computer system in which the present invention may be used. The system includes a host processor 10 having at least one peripheral port 11. A peripheral input/output line 12 is connected between a peripheral adapter 14 and the host processor 10. The peripheral adapter 14 provides serial-to-parallel conversion of data, contains a buffer for storing one line of data for a printer 15, and provides handshaking between the host 10 and the printer 15. One such peripheral adapter is the 5430-1101 SIA system interface adapter available from the NCR Corporation of Dayton, Ohio 45479, U.S.A. A system interface adapter usable as the peripheral adapter (hereinafter PA) is also disclosed in U.S. Patent 4,387,441. Any of several standard line printers may be used for the printer 15. Line printers 6471-020X or 6430-0201 available from NCR Corporation may be used, or a BP Series Line Printer available from Dataproducts Corp., Canoga Park, California 91304, U.S.A. may be used. An input/output (1/0) cable 16 is connected between the PA 14 and the printer 15. The PA 14 has a PA interface circuit 17, and the printer 15 has a printer interface circuit 18 for connection on either end of the I/O cable 16. As is known, if the 1/0 cable 16 is less than about 15 metres long, the interface circuits 17 and 18 must be short line interface adapters. However, if the I/O cable 16 is between about 15 metres and 150 metres long, the interface circuits 17 and 18 must be long line interface adapters. Conventional short line interface adapters utilize single ended drivers and receivers at either end of the I/O cable 16, whereas conventional long line interface adapters utilize differential drivers and receivers. In the present invention, a PA interface circuit 17 is provided in the PA 14 which contains drivers and receivers which may accommodate both short line and long line configurations. The drivers and receivers of the PA interface circuit 17 may be changed between its short line configuration and its long line configuration by changing jumper blocks, to be discussed. The printer interface circuit 18 may be one of the conventional short line or long line adapters, or the printer interface circuit 18 may be similar to the PA interface circuit 17. Fig. 2 is a schematic diagram of one conventional arrangement of the prior art showing a single ended driver 20 and a single ended receiver 21, one on either end of a pair of conductors 22 and 23 of a short line I/O cable (I/O cable 16 of Fig. 1). The single ended driver 20 includes an amplifier 25 for placing a single bit on conductor 22. The single ended receiver 21 includes an amplifier 26 for taking the single bit off conductor 22. Termination resistors Rl and R2 form a pull-up and pull-down circuit, as is known. One end of Rl is connected to a +5 voltage source, and its other end is connected to the conductor 22, and one end of R2 is connected to the conductor 22, and its other end is grounded. Typically, Rl may be 220 ohms, and R2 may be 330 ohms. Conductor 23 is grounded at each end. A binary bit having either a high or a low value may be transmitted over the conductor 22 by driving the voltage on conductor 22 either high or low with the amplifier 25. Fig. 3 is a schematic diagram of one conventional arrangement of the prior art showing one of a differential driver 28 and a differential receiver 29 on either end of a pair of conductors 30 and 31 of a long line I/O cable (I/O cable 16 of Fig. 1). The differential driver 28 includes a differential amplifier 32 having its non-inverted output connected to one end of conductor 30, and its inverted output connected to one end of conductor 31. The differential receiver 29 has a differential amplifier 34 having its inverted input connected to the other end of conductor 31, and its non-inverted input connected to the other end of conductor 30. A resistor R3 is connected in series with a capacitor Cl, with the series connected between the inverted and non-inverted inputs of differential amplifier 34. Resistor R3 has a resistance of 150 ohms, and capacitor Cl has a value of 0.01 microfarads. As is known, a binary bit transmitted over conductors 30 and 31 has one value when conductor 30 has a high voltage and conductor 31 has a low voltage, and has a second value when the conductor 30 has a low voltage and the conductor 31 has a high voltage. When the input of the differential driver 28 goes high, the differential amplifier 28 drives conductor 30 high and conductor 31 low. When conductor 30 goes high and conductor 31 low, the output of the differential amplifier 34 is high. When the input of the differential driver 28 is low, the output of the differential receiver 29 is low. Fig. 4 is a schematic diagram showing the single ended receiver 21 of Fig. 2 with a driver circuit 36 of the present invention configured for use with a short line I/O cable of conductors 22 and 23. The driver circuit 36 includes a differential line driver 38, which may be 1/4 of an AM26LS31 device available from Texas Instruments Incorporated of Dallas, Texas, 75265, U.S.A. The non-inverted output of the differential line driver 38 in Fig. 4 is connected to one end of the conductor 22, which is the same as conductor 22 of Fig. 2. Pins 1 and 2 of a connection device 35 are provided at one end of the conductor 23, and pins 1 and 2 of a connection device 37 are provided which, when shorted, shunt one end of conductor 23 to ground. In the short line configuration of Fig. 4, a jumper J3 is in place for connecting pins 1 and 2 of connection device 37, and pins 1 and 2 of connection device 35 are left un¬ connected such that both ends of the conductor 23 are grounded and the inverted output of differential line driver 38 is not connected. Thus the driver circuit 36 of Fig. 4 has similar characteristics to the single ended driver 20 of Fig. 2. Fig. 5 is a schematic diagram showing the differential receiver 29 of Fig. 3 with the driver circuit 36 of the present invention configured for use with a long line I/O cable of conductors 30 and 31. The conductors 30 and 31 of Fig. 5 are the same as the conductors 30 and 31 of Fig. 3. In the configuration of Fig. 5, a jumper J5 is in place connecting the pins 1 and 2 of the connection device 35, and the jumper J3 is not in place, leaving the pins 1 and 2 of the connection device 37 un-connected. In the configuration of Fig. 5, the non-inverted output of the differential line driver 38 is connected to one end of the conductor 30, and the inverted output of the differential line driver 38 is connected, via jumper J5, to one end of the conductor 31. Thus the driver circuit 36 in the configuration of Fig. 5 has similar characteristics to the differential driver 28 of Fig. 3. Fig. 6 is a schematic diagram showing the single ended driver 20 of Fig. 2 with a receiver circuit 40 of the present invention configured for use with a short line I/O cable including conductors 22 and 23. The receiver circuit 40 actually includes all of the elements shown in the receiver circuits of both Fig. 6 and Fig. 7. However, for clarity, only those elements included in the receiver circuit 40 by the including of jumper J2 (to be explained) are shown in Fig. 6, and only those elements included in the receiver circuit 40 by the including of jumper J4 (to be explained) are shown in Fig. 7. The receiver circuit 40 includes a differential line receiver 42 which may be 1/4 of an AM26LS33 device available from Texas Instruments Incorporated. A connection device having pins 1 and 2 at portion 43a, pins 3 and 4 at portion 43b, and pins 17 and 18 at portion 43c, is provided. With the jumper J2-1 in place, pins 1 and 2 of the connection device portion 43a are connected, grounding each end of the conductor 23. Termination resistors R4 and R5 form a pull-up and pull-down circuit which is connected to conductor 22 by the connecting of pins 3 and 4 of the connection device portion 43b with jumper J2-2. Resistor R4 may be a 220 ohm resistor, and resistor R5 may be a 330 ohm resistor. A resistor R6, a diode Dl and a capacitor C2 are all connected to the non- inverted input of the differential amplifier 42 by connecting pins 17 and 18 of connection device portion 43c by jumper J2-2. The resistor R6 is a 220 ohm resistor and capacitor C2 is a 0.1 microfarad capacitor. When connected as shown in Fig. 6, a reference voltage of about 0.75 volts is established on the non-inverted input of the differential amplifier 42. A connection device portion 45a having pins 1 and 2 is provided between the non-inverted input of the differential amplifier 42 and the conductor 23. In the arrangement of Fig. 6, when the voltage on the conductor 22 is driven by the driver 25 above the reference voltage of 0.75 volts on the non- inverted input of the differential amplifier 42, its output will go negative. Thus, in the arrangement of Fig. 6, the receiver circuit 40 acts like the single ended receiver 29 of Fig. 2 with an inverter. Fig. 7 is a schematic diagram showing the differential driver 28 of Fig. 3 with the receiver circuit 40 of the present invention configured for use with a long line I/O cable including conductors 30' and 31'. The conductors 30' and 31' of Fig. 7 are similar to the conductors 30 and 31 of Fig. 3. The jumpers J2-1, J2-2 and J2-3 of Fig. 6 are not in place, so the circuit elements shown in Fig. 6 are not in the circuit and are omitted in Fig. 7 for clarity. The non-inverted input of the differential line receiver 42 is connected to one end of conductor 30. Pins 1 and 2 of a connection device portion 45a are connected by a jumper J4-1, thus connecting the inverted input of the differential line receiver 42 to one ejid of conductor 31. A resistor R7 in series with a capacitor C3 are connected between conductors 30 and 31 by connecting pins 3 and 4 of a connection device portion 45b by a jumper J4-2. The resistor R7 has a resistance of 150 ohms, and the capacitor C3 has a value of 0.01 microfarads. Thus in the configuration of Fig. 7, the receiver circuit 40 functions as a differential receiver similar to the differential receiver 29 of Fig. 3. Figs. 8A and 8B, assembled as shown in Fig. 9, form a schematic diagram for a complete driver circuit for a typical PA-to-printer connection. The circuits of Figs. 8A and 8B have three quadruple differential line driver devices 45, 46 and 47. Driver devices 45 and 46 receive eight data bits (MDAT1-MDAT8) from the PA 14 (see Fig. 1). Driver device 47 receives a parity bit (MDAT9), a strobe signal (STROBE*), an advance signal (ADVANCE) and a buffer clear signal (BOFCLR). The non-inverted outputs of the driver devices 45, 46 and 47 are connected to the pins (pins 1-11 and 36) of a pin connector J6 for connection to a first set of conductors in an I/O cable (I/O cable 16 of Fig. 1). The inverted outputs of the line driver devices 45, 46 and 47, are connected to the odd numbered pins of a connection device 50. The even numbered pins of the connection device 50 are connected to the even numbered pins of a second connection device 52 by a bus 53. The odd numbered pins of the connection device 52 are grounded, and the even numbered pins of the device 52 are connected to a second set of conductors of the I/O cable (I/O cable 16 of Fig. 1). A jumper block J3 (not shown) may be used to jumper the even numbered pins with corresponding odd numbered pins of the connection device 52 to form the short line configuration of Fig. 4, and a jumper block J5 (not shown) may be used to jumper the even numbered pins with corresponding odd numbered pins of the connection device 50 to form the long line configuration of Fig. 5. The connection devices 35 and 37 of Figs. 4 and 5 correspond to pins 1 and 2 of connection devices 50 and 52 respectively. It will thus be understood that the line driver device 38 of Figs. 4 and 5 receives data bit MDAT1, and outputs DATA 1 and DATA 1 RTN bits on its outputs. Figs. 10A, 10B and IOC, assembled as shown in Fig. 11, form a schematic diagram for a complete circuit for a typical printer-to-PA connection. The circuit of Fig. 10A has a quadruple differential line receiver device 55 whose outputs provide a ready signal (READY*), a demand signal (DMND*), a top of form signal (TOF*) and a parity error signal (PARERR*) to the PA 14 responsive to inputs from the printer 15 (see Fig. 1). Connection device 56 of Figs. 10B and IOC, and connection device 57 of Fig. 10B are provided having their pins connected to the inputs of the differential line receiver device 55 of Fig. 10A such that when a jumper block J2 (not shown) is provided for connecting corresponding pins of the connection device 56, the differential line receiver device 55 is configured for receipt, of signals from a short line I/O cable, and when a jumper block J4 (not shown) is provided for connecting corresponding pins of the header device 57, the differential line receiver device 55 is configured for receipt of signals from a long line I/O cable. Selected pins (see Table I) of the pin connector J6 receive signals from the printer 15, and, dependent on the presence of either jumper J2 or J4, provide the receiver device 55 in either the short line or long line configuration. The pin numbers of connection device portions 42a, 43b and 43c of Fig. 6 correspond to the pin numbers of connection device 56, and the pin numbers of the connection device portion 45a of Figs. 1 and 7 and connection device portion 45b of Fig. 7 correspond to the pin numbers of connection device 57 of Fig. 10b. Thus, Fig. 6 shows the configuration for the receipt of the ON LINE and ON LINE RTN signals from the printer 15 for the generation of the READY* signal for the PA 14 for use with a short line I/O cable configuration, and Fig. 7 shows the configuration for the receipt of the ON LINE and ON LINE RTN signals from the printer 15 for the generation of the READY* signal for the PA 14 for use with a long line I/O cable configuration. Table I shows the pin assignments of the pin connector J6 for signals to and from the printer 15, the pins of the connector J6 (other than the pin 16) being connected to conductors of the I/O cable. TABLE I PIN DATA PIN DATA 1 DATA 1 20 DATA 1 RTN 2 DATA 2 21 DATA 2 RTN 3 DATA 3 22 DATA 3 RTN 4 DATA 4 23 DATA 4 RTN 5 DATA 5 24 DATA 5 RTN 6 DATA 6 25 DATA 6 RTN 7 DATA 7 26 DATA 7 RTN 8 DATA 8 27 DATA 8 RTN 10 PAPER ADV 29 PAPER ADV RTN 11 BUFFER CLEAR 30 BUFFER RTN 12 ON LINE : RTN 31 ON LINE 13 PARITY ERR 32 PAR ERR RTN 14 TOF - 33 TOF RTN 15 DEMAND RTN 34 DEMAND 16 GROUND 35 — 17 — 36 STROBE 18 STROBE RTN 37 — 19 — —— __. -—

Claims: CLAIMS : 1. An interface circuit (17) for use with a computer input/output cable (16) connected to a computer peripheral device (15) including a plurality of drivers (38) each having input means for receiving data bits, and output means for driving conductor means in the input/output cable, characterized by electrical network means adaptable for making each of said drivers compatible with a first predetermined length of input/output cable or with a second predetermined length of input/output cable, and connection means (35, 37, J3, J5) for selectively adapting said electrical network means so that said drivers are selectively made compatible with either said first predetermined length of said second predetermined length of input/output cable. 2. An interface circuit according to claim 1, characterized in that each of said drivers (36) comprises a differential line driver having a first and a second output, said electrical network means being arranged to connect said first outputs of said differential line drivers to a first set of conductors (22; 30) in said input/output cable, and said electrical network means and said connection means (35, 37, J3, J5) being arranged to connect said second outputs of said differential line drivers to a second set of conductors (23; 31) in said input/output cable for the purpose of rendering said differential line drivers compatible with said first predetermined length of input/output cable, and being arranged to connect said second set of conductors to ground for the purpose of rendering said differential line drivers compatible with said second predetermined length of input/output cable. 3. An interface circuit according to claim 2, characterized in that said connection means includes jumper means (J3, J5) for selectively connecting said second set of conductors (23; 31) to ground or to said second outputs of said differential line drivers (38) . 4. An interface circuit according to either claim 2 or claim 3, characterized by a plurality of receivers (42) each having input means for receiving data bits from conductor means in the input/output cable, and output means for providing an output signal related to the data bits received on its input means, further electrical network means adaptable for making each of said receivers compatible with said first predetermined length of input/output cable or with said second predetermined length of input/output cable, and further connection means (J2, J4) for selectively adapting said further electrical network means so that said receivers (42) are selectively made compatible with either said first predetermined length or said second predetermined length of input/output cable. 5. An interface circuit according to claim 4, characterized in that each of said receivers (42) comprises a differential line receiver having a first and a second input, said further electrical network means being arranged to connect said first inputs of said differential line receivers to a third set of conductors (22'; 30') in said input/output cable, and said further electrical network means and said further connection means (J2, J4) being arranged to connect said second inputs of said differential line receivers (42) to a fourth set of conductors (23'; 31') in said input/output cable for the purpose of rendering said differential line receivers compatible with said first predetermined length of input/output cable, and being arranged to connect said fourth set of conductors to ground for the purpose of rendering said differential line receivers compatible with said second predetermined length of input/output cable. 6. An interface circuit according to claim 5, characterized in that said further electrical network means includes reference voltage means (C2, Dl, R6), said further connection means being arranged to connect said reference voltage means to said second inputs of said differential line receivers when said differential line receivers (42) are rendered compatible with said second predetermined length of input/output cable so as to place a reference voltage on each of these inputs. 7. An interface circuit according to claim 6, characterized in that said further electrical network means includes pull-up and pull-down termination resistors (R4, R5) for each of said first inputs of said differential line receivers (42), said further connection means being arranged to connect said pull-up and pull-down termination resistors to said first inputs of said differential line receivers when said differential line receivers are rendered compatible with said second predetermined length of input/output cable. 8. An interface circuit according to claim 7, characterized in that said further electrical network means includes a plurality of series resistor- capacitor circuits (C3, R7), said further connection means being arranged to connect each of said series resistor-capacitor circuits between said first and second inputs of a respective one of said differential line receivers (42) when said differential line receivers are rendered compatible with said first predetermined length of input/output cable. 9. An interface circuit according to claim 8, characterized in that said further connection means includes jumper means (J2, J4) for selectively connecting said fourth conductors (23'; 31') to ground or to said second inputs of said differential line receivers (42), for selectively connecting said reference voltage means (C2, Dl, R6) to said second inputs of said differential line receivers (42), for selectively connecting said pull-up and pull-down termination resistors (R4, R5) to said first inputs of said differential line receivers, and for selectively connecting said series resistor-capacitor circuits (C3, R7) between said first and second inputs of said differential line receivers.

Inventors: JALALI BAHMAN, JALALI, BAHMAN
Applicants: NCR CO, NCR CORPORATION
Application year: 1987
Main classification: H04L25
IPC codes: G06F3, H03K19, H04L25