Single wire bus interface for multidrop applications

• US 6,298,066 B1
• Filed: 04/14/1999
• Issued: 10/02/2001
• Est. Priority Date: 04/14/1999
• Status: Expired due to Fees

• Current Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Original Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Inventors: Ashburn, Michael A., Allen, Charles M., Wettroth, John M.
• Primary Examiner(s): Myers, Paul R.
• Application Number:
  US09/292,073
• Time in Patent Office: 902 Days
• Field of Search: 370/449, 710/100, 710/29
• US Class Current: 370/449
• CPC Class Codes: H04L 12/403 with centralised control, e.g. polling

Abstract

The present invention enables data communications between multiple devices over a single wire bus. This single-wire interface can be used for sensors, amplifiers, analog-to-digital converters (ADCs), or any other circuit which would normally have an electrical output. Advantages of the present invention include a reduction in device pin count, conservation of the limited number of I/O pins on the control device, and reduced board layout complexity. Speaking generally, each slave device coupled to the single wire bus interface is assigned a different response time window. This enables multiple slave devices to respond to an initial trigger signal generated by the master device without overlapping responses being generated on the single wire bus interface. A suitable slave electrical device includes application circuitry providing state information for the electrical device, an input/output pin suitable for making an electrical coupling external to the electrical device, and a single wire bus interface coupled to the input/output pin and the application circuitry. The single wire bus interface has conversion function circuitry defining a specific response time window for the electronic device. Further, the single wire bus interface is responsive to a start signal received on the input/output pin to generate a response signal within the specific response time window, the response signal indicative of the state information for the electrical device.

Claims

1. A method for controlling communication over a single wire bus interface for a multidrop circuit, the multidrop circuit including a master device and a first slave device coupled together via the single wire bus, the first slave device being assigned a first window of response, the method comprising the steps of:

initiating a timing sequence by transmitting a start command on the single wire bus interface;

during the first window of response, communicating data associated with the first slave device; and

providing a conversion function circuitry that includes a plurality of flip-flop devices, the flip-flop devices arranged to delay a response signal until the first window of response.

2. A method as recited in claim 1, wherein the start command is generated by the master device.

3. A method as recited in claim 1, wherein an idle state for the single wire bus interface is high, and the start command corresponds to pulling the single wire bus interface low.

4. A method as recited in claim 3 wherein the timing sequence is initiated upon a falling edge of the start command.

5. A method as recited in claim 4 wherein the step of communicating data associated with the first slave device includes a response of pulling the single wire bus interface low.

6. A method as recited in claim 5 wherein the data associated with the first slave device includes data encoded as a time delay between the falling edge of the start command and a falling edge of the response.

7. A method as recited in claim 6 wherein the first slave device is an analog-to-digital converter and the time delay between the falling edge of the start command and the falling edge of the response is a function of an analog value measured by the analog-to-digital converter.

8. A method as recited in claim 7 wherein the analog-to-digital converter is a temperature sensor and the analog value corresponds to temperature.

9. A method as recited in claim 7 wherein the analog-to-digital converter is a voltage sensor and the analog value corresponds to voltage.

10. A method as recited in claim 7 wherein the analog-to-digital converter is a pressure gauge and the analog value corresponds to pressure.

11. A method as recited in claim 7 wherein the analog-to-digital converter is an accelerometer and the analog value corresponds to acceleration.

12. A method as recited in claim 1 wherein the first slave device is one of a plurality of slave devices coupled on the single wire bus interface, each of said plurality of slave devices being assigned a unique window of response such that there exists a plurality of response windows forming the timing sequence, the method further comprising the steps of communicating data associated with each slave device during the associated unique window of response.

13. A method as recited in claim 12 wherein each unique window of response is a unique time period selected such that no overlap exists between each unique window of response.

14. A single wire communications protocol enabling a master device to control communications for a multidrop circuit over a single wire bus interface, the multidrop circuit suitable arranged to couple the master device and a plurality of slave devices via the single wire bus interface, each slave device being assigned a unique window of response, the protocol comprising instructions for:

initiating a timing sequence by transmitting a start command on the single wire bus interface;

processing data received during each window of response including interpreting data received during each unique window of response as corresponding to the particular slave device assigned to that unique window of response; and

delaying each window of response with conversion function circuitry which includes a plurality of flip-flop devices arranged to delay a response signal for each slave device until each slave devices unique window of response.

15. A single wire communications protocol as recited in claim 14 further comprising the step of determining each time delay between the start command and every response received.

16. A single wire communications protocol as recited in claim 15 wherein a first of the plurality of slave devices is an analog-to-digital converter and the time delay between the start command and a response from the first slave device is a function of an analog value measured by the analog-to-digital converter.

17. An electrical device suitable for use as a slave device in a multidrop application, the multidrop application arranged for data communications between a master device and multiple slave devices over a single wire bus, each electrical device being assigned a different response time window, the electrical device comprising:

application circuitry providing state information for the electrical device;

an input/output pin suitable for making an electrical coupling external to the electrical device; and

a single wire bus interface coupled to the input/output pin and the application circuitry, the single wire bus interface having conversion function circuitry defining a specific response time window for the electronic device, the single wire bus responsive to a start signal received on the input/output pin to generate a response signal within the specific response time window, the response signal indicative of the state information for the electrical device;

wherein the conversion function circuitry includes a plurality of flip-flop devices, the flip-flop devices arranged to delay the response signal until the specific response time window.

18. An electrical device as recited in claim 17, the application circuitry operable to generate the state information for the electrical device in response to a sensed an analog value.

19. An electrical device as recited in claim 18 wherein the analog value to which the application circuitry is responsive to temperature.

20. An electrical device as recited in claim 18 wherein the analog value to which the application circuitry is responsive is pressure.

21. An electrical device as recited in claim 18 wherein the analog value to which the application circuitry is responsive is a voltage potential.

22. An electrical device as recited in claim 18, the electrical device further comprising an internal clock coupled to the single wire bus interface, the single wire bus interface using the internal clock to track time lapse in order to generate the response signal within the specific response time window.

23. An electrical device as recited in claim 22, the internal clock including a crystal oscillator.

24. A multidrop circuit comprising:

a single wire bus;

a master device coupled to the single wire bus;

a first slave device coupled to the single wire bus and assigned a specific response time window, the first slave device including;

application circuitry providing state information for the slave device; and

a single wire bus interface coupled to the single wire bus and the application circuitry, the single wire bus interface having conversion function circuitry defining the specific response time window for the electronic device, the single wire bus interface responsive to a start signal transmitted on the single wire bus to generate a response signal within the specific response time window, the response signal indicative of the state information for the slave device;

wherein the conversion function circuitry includes a plurality of flip-flop devices, the flip-flop devices arranged to delay the response signal until the specific response time window.

25. A multidrop circuit as recited in claim 24, the application circuitry operable to generate the state information for the slave device in response to a sensed an analog value.

26. A multidrop circuit as recited in claim 25 wherein the analog value to which the application circuitry is responsive to temperature.

27. A multidrop circuit as recited in claim 25 wherein the analog value to which the application circuitry is responsive is pressure.

28. A multidrop circuit as recited in claim 25 wherein the analog value to which the application circuitry is responsive is a voltage potential.

29. A multidrop circuit as recited in claim 25, the slave device further comprising an internal clock coupled to the single wire bus interface, the single wire bus interface using the internal clock to track time lapse in order to generate the response signal within the specific response time window.

30. A multidrop circuit as recited in claim 29, the internal clock including a crystal oscillator.

31. A multidrop circuit as recited in claim 24 wherein the master device includes a central processing unit.

32. A multidrop circuit as recited in claim 24 wherein the master device includes a microprocessor.

33. A multidrop circuit as recited in claim 24 wherein the master device includes a digital signal processor.