Communication device with circuitry to promote cascade series connection including identification of device position in the series and sensing the end device in the series

• US 6,523,070 B1
• Filed: 02/23/2000
• Issued: 02/18/2003
• Est. Priority Date: 07/23/1996
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Company (HP Inc.)
• Original Assignee: 3Com Corporation (HP Inc.)
• Inventors: Smith, David R., Walker, Christopher, Stapleton, Nicholas, Overs, Patrick M.
• Primary Examiner(s): EL HADY, NABIL M
• Application Number:
  US09/230,391
• Time in Patent Office: 1,091 Days
• Field of Search: 709/225, 709/226, 709/229, 709/250, 709/253, 710/126, 710/129
• US Class Current: 709/250
• CPC Class Codes: G06F 13/4068 Electrical coupling
• CPC Class Codes: G06F 13/4072 Drivers or receivers G06F13/4086 takes precedence; for multistate logic circuits H03K19/0002

Abstract

A communications apparatus comprising a plurality of communication devices each having a plurality of ports and a data bus interconnecting the plurality of units, wherein each device is provided with means enabling the device to detect automatically its position on the data bus.

Claims

1. A network communication device comprising a plurality of ports whereby connection can be made to network equipment and connection means arranged to enable connection to two other similar devices whereby a plurality of said devices may be cascade connected, the device comprising sensing means arranged to sense whether the device is at the end of a series of cascade connection devices, said sensing means comprising:

first and second complementary circuitry providing first and second outputs respectively and having first and second interconnections respectively, the first and second circuitry being arranged whereby said first output has a first value in the event that said first interconnection is connected to a second interconnection in another device and a second value if it is not so connected, and whereby said second output has a first value in the event that said second interconnection is connected to a first interconnection in another device and a second value if it is not so connected; and

means arranged to indicate that said device is at the end of a series of cascade connected devices when one of said first and second outputs takes its second value;

wherein said first circuitry comprises means arranged to drive said first interconnection to a first logical level and said first output to take said first value for said second value, dependent on whether current is drawn via said first interconnection, and said second circuitry comprises means arranged to pull said second interconnection to a second logical level and to sense when said second interconnection is driven to said first logical level;

whereby connection between said second circuitry in one device and said first circuitry in other device provides an active signal to said first circuitry of said other device and causes a current driver in series with a resistor in said second circuitry of said one device to drive current through said resistor providing an output of logical level dependent on current flow through the resistor.

2. A network communication device according to claim 1, further comprising a data bus termination device which is activated when it is determined that the device is at the end of a series of cascade connected devices.

3. A network communication device comprising a plurality of ports whereby connections can be made to network equipment and connection means arranged to enable connection to two other similar devices whereby a plurality of said devices may be cascade connected, the device comprising means for determining an identification of its position in a series of cascade connected devices, said means comprising:

an input;

an output arranged to be connected to the input of another device when devices are cascade connected;

means arranged to generate pulses of a predetermined duration and to output said pulses via said output when no signal is received via said input;

means arranged to receive pulses via said input, to increment the duration of said pulses by said predetermined duration and to output said pulses as thus incremented via said output; and

means arranged to determine the identification of the position of the device by discriminating on the basis of pulse length determined by the duration of the pulses received at said input.

4. A communication apparatus comprising a plurality of network communication devices each being a device according to claim 3, the devices being interconnected via said connection means to form a data bus.

5. Apparatus according to claim 4 further comprising a cascade connection device connected between said connection means of at least one of said network communication devices and the respective portions of the data bus to enable the removal of that communication device without breaking the cascade connection of the remaining units.

6. A communications apparatus comprising a plurality of network communication devices each being a device according to claim 3, the devices being interconnected via said connection means to form a data bus.

7. Apparatus according to claim 6 further comprising a cascade connection device connected between said connection means of at least of said network communication devices and the respective portions of the data bus to enable the removal of that communication device without breaking the cascade connection of the remaining units.

8. A network communication device comprising a plurality of ports for connection to other network equipment and connection means for connection of the device to two other similar devices whereby a series of devices can be cascade connected, the device comprising sensing means for sensing whether the devices are at an end of said series, said sensing means comprising:

a first circuit having a first terminal, an amplifier having an input connected to said first terminal, and a first output having a first logical level in the absence of an active signal at said first terminal and a second logical level in the presence of an active signal at said first terminal; and

a second circuit having a second terminal, a current driver in series with a resistor and having a control terminal coupled to said second terminal and an amplifier having an input coupled to said resistor to provide an output logical level dependent on current flow through said resistor, and means for coupling said second terminal to a voltage rail, whereby connection of said second terminal in one device to said first terminal in other device provides said active signal in said first circuit and causes said current driver to drive current through said resistor.