Digital communication system and method

• US 6,384,723 B1
• Filed: 11/02/1998
• Issued: 05/07/2002
• Est. Priority Date: 11/02/1998
• Status: Expired due to Term

• Current Assignee: Pittway Corporation (Honeywell International Inc.)
• Original Assignee: Pittway Corporation (Honeywell International Inc.)
• Inventors: Clow, Robert J., Tice, Lee D., Keeler, Manley S.
• Primary Examiner(s): Crosland, Donnie L.
• Application Number:
  US09/184,409
• Time in Patent Office: 1,282 Days
• Field of Search: 340/513, 340/505, 340/506, 340/512, 340/511, 340/509, 340/533, 340/537, 340/660, 340/661, 340/3.1, 324/500, 324/524
• US Class Current: 340/513
• CPC Class Codes: H04L 7/0008 Synchronisation information channels, e.g. clock distribution lines
• CPC Class Codes: H04L 7/06 the synchronisation signals differing from the information signals in amplitude, polarity or frequency or length

Abstract

A communication protocol facilitates transmission at maximum rates for various types of cables. Signal to noise characteristics are improved by using voltage waveforms. The protocol can be used to transmit information between a common control unit and a plurality of spaced apart devices coupled thereto. Alternately, the protocol can be used for transmission of information between devices. The common control unit transmits clock pulses, while in a low impedance state. The devices respond to the clock pulses and transmit data on the communications link, in a low impedance state, when the common control unit has assumed a high impedance state. Clock signals and data signals are separated to improve signal to noise characteristics by transmitting same with opposite polarities. A clock detection circuit responds to the polarity of the clock pulses. A data detection circuit responds to the polarity of the data pulses.

Claims

1. A communication apparatus comprising:

a voltage drive source;

a multi-conductor communications medium, coupled to the source, wherein the source incudes drive circuitry for impressing on at least one of the conductors of the medium a plurality of spaced apart, voltage-type clock pulses of a first polarity relative to two of the conductors;

an electrical device, coupled to the medium, wherein the device includes receiver circuitry for detecting the voltage-type clock pulses and for generating in the device electrical signals indicative thereof, wherein the device further includes transmitter circuitry for producing a plurality of spaced apart voltage drive data pulses on the at least one conductor, at least some of which are interspersed between respective pairs of clock pulses and having a second, different, polarity relative to the two conductors.

2. An apparatus as in claim 1 wherein, the device includes circuitry for establishing a common datum and wherein relative, to the common datum, the first polarity is the opposite of the second polarity.

3. An apparatus as in claim 1 wherein the source includes circuitry for generating the voltage clock pulses with a relatively low output impedance and for switching to a relatively high output impedance between clock pulses.

4. An apparatus as in claim 3 wherein the generating circuitry includes circuitry for generating first and second spaced apart bounding waveforms with the clock pulses positioned therebetween.

5. An apparatus as in claim 3 wherein the source intermittently provides electrical energy to the device.

6. An apparatus as in claim 5 wherein the generating circuitry generates bounding waveforms of the first polarity.

7. An apparatus as in claim 5 wherein the source provides electrical energy at least during clock pulses.

8. An apparatus as in claim 1 wherein the device contains an energy source and wherein the transmitter circuitry provides electrical energy to the at least one conductor from the energy source.

9. An apparatus as in claim 8 wherein the energy source is powered off of the medium.

10. An apparatus as in claim 4 wherein subsequent to one of the bounding signals, a medium settling delay is provided before transmission is initiated.

11. An apparatus as in claim 1 wherein the data pulses are transmitted with a substantially constant width.

12. An apparatus as in claim 1 wherein the data pulses are transmitted with at least first and second different widths.

13. A communication apparatus comprising

a voltage drive source;

at least a two-wire medium for communication, coupled to the source, wherein the source includes drive circuitry for impressing on the medium a plurality of spaced apart, voltage-type clock pulses of a first polarity across two of the wires;

an electrical device, coupled to the medium, wherein the device includes circuitry for detecting the voltage-type clock pulses and for generating in the device electrical signals indicative thereof;

wherein the device contains an energy source; and

wherein the device further includes transmitter circuitry for driving the medium, from the energy source in the device, with a plurality of spaced apart voltage-type data pulses, and having a second, different polarity across the two wires.

14. An apparatus as in claim 13 wherein the source includes circuitry for generating voltage-type clock pulses with a relatively low output impedance and for switching to a relatively high output impedance between clock pulses.

15. An apparatus as in claim 14 wherein the generating circuitry includes circuitry for generating first and second spaced apart bounding waveforms with the clock pulses positioned therebetween.

16. An apparatus as in claim 14 wherein the device establishes at least one threshold detection level and includes circuitry coupled thereto to detect the clock pulses.

17. An apparatus as in claim 13 wherein the device establishes at least one threshold detection level and includes circuitry coupled thereto to detect the data.

18. An apparatus as in claim 13 wherein the source intermittently provides electrical energy to the device when a voltage across the two wires is higher than a predetermined level.

19. An apparatus as in claim 13 wherein the data pulses are transmitted with a substantially constant width.

20. An apparatus as in claim 13 wherein the data pulses are transmitted with at least first and second different widths.

21. An apparatus as in claim 13 wherein prior to transmission of any data pulses, a medium settling period is provided.

22. An apparatus as in claim 13 wherein prior to transmission of any clock pulses a medium settling time is provided.

23. An apparatus as in claim 15 wherein the generating circuitry includes delay circuitry for providing a medium settling time interval prior to initiating transmission of any clock and data signals.

24. A communications system interface circuit with first and second terminals comprising:

circuitry for providing temporally spaced apart framing signals at the terminals with an amplitude corresponding to a first voltage level, having a first polarity;

circuitry for providing a plurality of spaced apart first pulses at the terminals, between spaced apart framing signals, an amplitude less than the first voltage level and with the first polarity; and

circuitry for receiving, at the terminals, spaced apart second voltage pulses, at least some of which are interspersed between pairs of first pulses, and having a polarity opposite that of the first polarity.

25. A circuit as in claim 24 which includes threshold establishing circuitry for detecting the second voltage pulses.

26. A circuit as in claim 25 which includes a power supply for providing electrical energy to the terminals simultaneously with the framing signals.

27. A circuit as in claim 24 which includes circuitry for establishing a selected voltage level with an amplitude between the amplitude of the first pulses and an amplitude of the second pulses, wherein the selected voltage level is temporally spaced between the first pulses and is present in the absence of the second pulses.

28. A circuit as in claim 24 which includes switching circuitry for providing the plurality of first pulses with a low output impedance.

29. An electrical unit comprising:

circuitry for detecting a transition of a voltage signal of a selected polarity through a first threshold thereby defining one of a framing signal start transition and a framing signal end transition;

circuitry for detecting at least one voltage transition through a second threshold, less than the first threshold, thereby defining one of a plurality of clock pulses;

circuitry for detecting at least one voltage transition through a third threshold thereby defining one of a plurality of data pulses wherein the data pulses exhibit an amplitude having a polarity opposite the polarity of the framing signals.

30. A unit as in claim 29 which includes a power supply wherein the power supply receives electrical energy from an exterior source in the presence of a selected signal.

31. A unit as in claim 30 which includes interface circuitry for coupling the unit to a communications link.

32. A unit as in claim 31 wherein the power supply receives electrical energy in the presence of the selected signal, from the link.

33. A unit as in claim 32 wherein the power supply transfers electrical energy to the link during selected time intervals.

34. In a communication system, a method of driving a waveform on a communication line comprising:

providing a start-frame indicator by altering a line voltage of a first polarity relative to a predetermined value;

generating clock pulse voltages with the first polarity and an amplitude that is different than the start frame indicator;

sending data pulses of a different polarity during the high impedance period of time;

providing an end-frame indicator for the message by returning the line voltage to the predetermined value.

35. A method as in claim 34 which includes:

switching to a high impedance state and decoupling from the communication line for a period of time between each clock pulse.

36. A method, as in claim 35, wherein the line voltage is driven to zero between each clock pulse prior to switching to the high impedance for decoupling a power supply from the communication line.

37. A method as in claim 35 where the devices coupled to the communication line exhibit a high impedance unless a selected device is transmitting a data value.

38. A method as in claim 34 wherein a stabilization period is provided immediately following the frame-start indicator prior to the first clock pulse.

39. A method as in claim 34 wherein multiple words are transmitted in the message.

40. A method as in claim 39 wherein one word in the message comprises an error detection check sum.

41. A communications method comprising:

generating a plurality of spaced apart voltage clock pulses, and transmitting the clock pulses with a first polarity in a low impedance state;

generating a plurality of voltage da pulses;

transmitting at least some of the voltage data pulses with a second polarity, opposite the first polarity, interspersed between pairs of clock pulses, and in the presence of a relatively high impedance state.

42. A method as in claim 41 which includes:

providing a clock pulse transmitting source with high and low output impedance states and switching the source to the low impedance state when clock pulses are being transmitted and to the high impedance state when data pulses are being transmitted from a data source.

43. A method as in claim 41 wherein the clock pulses are bounded by framing signals with the first polarity.

44. A method as in claim 43 wherein clock pulses are detected with a threshold having the first polarity and wherein data pulses are detected with a different threshold having the second polarity.

45. A method as in claim 44 which includes providing electrical energy at least during the clock pulses.

46. A method as in claim 44 wherein the framing signals are detected with a third threshold, greater than the threshold but having the first polarity.

47. An electrical unit couplable to a bidirectional communication link, the unit comprising:

interface circuitry having at least first and second threshold detection circuits wherein the detected thresholds have one polarity and a third threshold detection circuit wherein the third threshold has a different polarity and wherein the polarities are relative to a selected, common communication line.

48. An electrical unit as in claim 47 which includes programmable control circuits, coupled to the interface circuitry, and an ambient condition sensor coupled to the control circuits.

49. An electrical unit as in claim 48 wherein the ambient condition sensor is one of a fire sensor, a position sensor and a motion sensor.

50. An electrical unit as in claim 47 wherein the interface circuitry includes circuitry having a high impedance state for receipt of signals from the link associated with the first and second thresholds and having a low impedance state for signals output to the link wherein the output signals are associated with the third threshold.

51. An electrical unit as in claim 47 which includes programmable control circuitry, coupled to the interface circuitry, and output function circuitry coupled to the control circuitry.

52. A communication system having a bidirectional communications medium comprising:

a plurality of electrical units wherein the medium enables a selected unit to communicate and the units each include communications interface circuitry, couplable to the medium, wherein that circuitry selectively exhibits a first output impedance and a second, lower output impedance wherein the interface circuitry includes drive circuitry for impressing a selected signaling voltage on the medium with the second output impedance; and

detection circuitry for comparing a voltage on the medium to a voltage expected to be present on the medium and for terminating unit communication, at least temporarily, in response to a difference therebetween.

53. A system as in claim 52 wherein the units each include control circuitry for coupling a multi-state data bit sequence to the interface circuitry wherein one state corresponds to impressing the signaling voltage on the medium with the second output impedance and the other state corresponds to not impressing the signaling voltage and exhibiting the first output impedance.

54. A system as in claim 53 wherein at least some of the units include ambient condition sensors.

55. A system as in claim 54 wherein the control circuitry, in at least some of the units, includes a programmed processor.

56. A prioritizing process, usable with a plurality of energy supplying devices that communicate via a medium, the process comprising:

impressing, using energy from a communicating device, a discontinuous voltage sequence, corresponding to an indicator, on the medium wherein the sequence has at least two states;

comparing a discontinuous voltage sequence present on the medium to the impressed sequence, and, in response to a difference therebetween, terminating the process for a period of time.

57. A process as in claim 56 wherein the sequence is impressed on the medium with first and second output impedances wherein one output impedance corresponds to one of the states, wherein the presence of a selected voltage value is associated with a lower output impedance value and another voltage value is associated with a higher output impedance value.

58. A process as in claim 57 which includes coupling electrical energy to the medium while in the lower output impedance state.

59. A process as in claim 56 which includes impressing at least two independent discontinuous voltage sequences, corresponding to respective different indicators, on the medium;

comparing a sequence actually present on the medium with each of the impressed sequences and, in response to a detected difference between the sequence present on the medium and a respective one of the independent sequences, terminating the impressing step with respect to that sequence.

60. A process as in claim 59 which includes intermittently coupling electrical energy to the medium during the impressing step.

61. A communication system which provides an access time for messages with multiple devices capable of transmitting information via a communications medium at the same time during the access time, the system comprising:

a plurality of devices each having circuitry capable of transmitting a signal on the communication medium including circuitry in the devices for monitoring the communication medium, and including energy storage circuits in at least some of the devices and wherein stored energy in the devices is used to transmit a voltage signal on the communication medium and where the devices wait to start transmitting until an access time is provided;

decision logic in the devices to stop transmitting during the access time if a mismatch occurs; and

wherein

if a device stopped transmitting because of a mismatch, that device will retry transmitting during the next access time.

62. A system as in claim 61 wherein at least some of the devices include ambient condition sensors.

63. A system as in claim 61, wherein the devices include circuitry to transmit a message using a synchronized access start time.

64. A system as in claim 61, Wherein a respective device stops trying to transmit a message once the devices complete their message without a mismatch.

65. A system as in claim 61, where the device transmissions are in response to a group message requesting a group of devices to respond with a message.

66. A system as in claim 64, where the devices include circuitry to again try to send a message at least once all other messages from other devices are completed without a mismatch.

67. A system as in claim 64, wherein at least some of the devices again try to send a respective message if a new message is established in the device.

68. A communications apparatus comprising:

a voltage drive source;

at least a two wire communications medium, coupled to the source, wherein

the source includes drive circuitry for impressing on the medium a plurality of voltage-type frame defining signals wherein

during a defined frame information can be transmitted on the medium and wherein

delay circuitry provides a medium settling delay at the beginning of a defined frame and before any information is transmitted.

69. An apparatus as in claim 68 which includes signal generating circuitry for, subsequent to the delay, transmitting a data interval start signal on the medium.

70. An apparatus as in claim 68 which includes circuitry, coupled to the medium for transmitting a plurality of spaced apart voltage-type data pulses with a polarity relative to a selected reference, opposite that of the frame defining signals.

71. An apparatus as in claim 68 which includes clock generation circuitry for generating on the medium at least one clock pulse between selected data pulses wherein the clock pulses have a polarity opposite that of the data pulses.