Method and apparatus for providing a high throughput two-conductor serial interface with support for slave device detection

• US 5,758,098 A
• Filed: 05/12/1994
• Issued: 05/26/1998
• Est. Priority Date: 05/12/1994
• Status: Expired due to Term

• Current Assignee: Apple Computer Incorporated (Apple Inc.)
• Original Assignee: Apple Computer Incorporated (Apple Inc.)
• Inventors: Gong, Andrew, Townsley, David B.
• Primary Examiner(s): Harvey, Jack B.
• Assistant Examiner(s): WILEY, DAVID ARMAND
• Application Number:
  US08/241,738
• Time in Patent Office: 1,475 Days
• Field of Search: 395/325, 395/250, 395/800, 395/282, 395/283, 395/290, 371/15.1, 439/41
• US Class Current: 710/301
• CPC Class Codes: G06F 13/4291 using a clocked protocol

Abstract

A master agent and a slave agent are interconnected over a two-conductor bus system. One conductor is utilized to transfer data signals between the agents and the second conductor is utilized to transfer a clock signal between the agents. The master agent includes a single data port for both input and output. The slave agent includes two data ports: an input port and an output port. The input port and the output port are coupled to a single conductor, thereby allowing data to be input to and output from the slave agent on a single line. An open collector device is situated between the output port of the slave agent and the data conductor. Data is transferred between the master and slave agents by first synchronizing the agents. The agents are synchronized by first allowing the data conductor to obtain a high state. Upon sensing the data conductor high, the master agent drives the clock conductor to a low state. The slave agent responds by driving the data conductor low if the agent is ready for a transfer. The master agent then drives the clock conductor high in response to the slave agent driving the data conductor low. The slave agent then drives the data conductor high, and prepares for the data transfer.

Claims

1. A system for transferring data between a master agent and a slave agent, said system comprising:

a first signal conveyance medium for transferring a clock signal from said master agent to said slave agent, said clock signal having a falling edge and a rising edge, said first signal conveyance medium including a first portion removably coupled to a second portion, first signal conveyance medium including circuitry for automatically pulling first signal conveyance medium to a first predetermined state when said first portion is coupled to said second portion and for automatically pulling first signal conveyance medium to a second predetermined state when said first portion is not coupled to said second portion;

a second signal conveyance medium for serially transferring data between said master agent and said slave agent;

said master agent being coupled to said first portion of first signal conveyance medium and said second signal conveyance medium, said master agent being configured to detect the first portion of the first signal conveyance medium being coupled to the second portion based on whether the first signal conveyance medium is automatically pulled to said first predetermined state or said second predetermined state;

said slave agent being coupled to said second portion of first signal conveyance medium and said second signal conveyance medium, said slave agent only receiving said clock signal, said slave agent including an input port for retrieving first data from said second signal conveyance medium on the rising edge of said clock signal and an output port for placing second data onto said second signal conveyance medium on the falling edge of said clock signal; and

a circuit coupled to said second signal conveyance medium and said output port, said circuit allowing said input port and said output port to share said second signal conveyance medium.

2. The system as defined in claim 1 wherein said slave agent further includes a shift register, said shift register storing said first data and said second data.

3. The system as defined in claim 1 wherein said circuit is an open collector device.

4. The system as defined in claim 1 wherein said second signal conveyance medium includes a third portion removably coupled to a fourth portion such that said slave agent and said master agent can be disconnected.

5. The system as defined in claim 1 wherein said circuitry includes a voltage source coupled to said first portion through a high impedance resistor and a ground source coupled to said second portion through a low impedance resistor.

6. The system as defined in claim 4 wherein a ground source is coupled to said third portion through a high impedance resistor and a voltage source is coupled to said fourth portion through a low impedance resistor.

7. The system as defined in claim 1 wherein said master agent includes control logic for:

determining whether the signal on said second signal conveyance medium is high or low;

tristating said first signal conveyance medium;

determining whether the signal on said first signal conveyance medium transitions low;

driving said first signal conveyance medium to a high state; and

determining whether the signal on said second signal conveyance medium transitions high in response to said driving.

8. The system as defined in claim 1 wherein said slave agent includes control logic for:

determining whether the signal on said first signal conveyance medium transitions from a high state to a low state;

driving said second signal conveyance medium to a low state; and

determining whether the signal on said first signal conveyance medium transitioned from a low state to a high state.

9. A method for synchronizing a computer system for serial communication with a power source using a first signal conveyance medium and a second signal conveyance medium, said power source being removably coupled to said computer system, said first signal conveyance medium for transferring said data and said second signal conveyance medium for transferring a clock signal, said method comprising the steps of:

(a) determining automatically whether the signal on said first signal conveyance medium is pulled to a first state or a second state; and

(b) determining said computer system is not coupled to said power source in response to the signal on said first signal conveyance medium being in said first state, otherwise synchronizing said computer system for transferring data serially to said power supply by,

(1) tristating said second signal conveyance medium,

(2) determining whether the signal on said second signal conveyance medium transitions low,

(3) driving said second signal conveyance medium to a high state, and

(4) determining whether the signal on said first signal conveyance medium transitions high in response to said driving.

10. The method as defined in claim 9 wherein said step (b)(2) comprises determining whether said signal on said second signal conveyance medium transitions low within a predetermined period of time after said tristating.

11. The method as defined in claim 9 wherein said step (b)(2) comprises repeating said steps (a) through (b)(1), provided said second signal conveyance medium remains in a high state for a predetermined period of time after said tristating.

12. The method as defined in claim 9 wherein said step (b)(4) comprises determining whether the signal on said first signal conveyance medium transitions high in response to said driving within a predetermined period of time after said driving.

13. The method as defined in claim 9 wherein said step (b)(4) comprises repeating steps (a) through (b)(3), provided said first signal conveyance medium remains in a low state within a predetermined period of time after said driving.

14. A method for synchronizing a first agent for transferring data serially to a second agent using a first signal conveyance medium and a second signal conveyance medium, said first and second agent being removably coupled together, said first signal conveyance medium for transferring said data and said second signal conveyance medium for transferring a clock signal, said method comprising the steps of:

(a) determining automatically whether the signal on said second signal conveyance medium is pulled to a first state or a second state; and

(b) determining said first agent is not coupled to said second agent in response to the signal on said first signal conveyance medium being in said first state, otherwise synchronizing the first agent for transferring data serially to the second agent by,

(1) determining whether the signal on said second signal conveyance medium transitions from a high state to a low state;

(2) driving said first signal conveyance medium to a low state; and

(3) determining whether the signal on said second signal conveyance medium transitioned from a low state to a high state.

15. The method as defined in claim 14, further comprising the step of determining whether said first agent is receiving data or sending data.

16. The method as defined in claim 15, further comprising the step of storing the data to be transferred into a data register if said first agent is sending data and storing a value of FF₁₈ into said data register if said first agent is receiving data.

17. The method as defined in claim 14 wherein said step (b)(2) comprises determining whether the signal on said second signal conveyance medium transitioned from a low state to a high state within a predetermined period of time after said driving.

18. The method as defined in claim 14 wherein said step (b)(2) comprises repeating said steps (b)(1) and (b)(2) if said second signal conveyance medium remains low for a predetermined period of time.

19. A method for transferring data serially between a first agent and a second agent using a first conductor and a second conductor, said first conductor having a first portion and a second portion removably connected by a first connector, said second conductor having a third portion and a fourth portion removably connected by a second connector, said first agent being coupled to said first portion and said third portion, said second agent being coupled to said second portion and said fourth portion, said first conductor for transferring said data and said second conductor for transferring a clock signal, said method comprising the steps of:

(a) synchronizing said first agent and said second agent, said synchronizing including,

determining automatically whether the signal on said first conductor is pulled to a first state or a second state,

determining automatically whether the signal on said second conductor is pulled to the first state or the second state,

determining both that said first portion and said second portion are not coupled together and that said third portion and said fourth portion are not coupled together in response to both said signal on said first conductor being in said first state and said signal on said second conductor being in said second state, otherwise,

re-charging a battery associated with the second agent;

tristating said second conductor,

determining whether the signal on said second conductor transitions low,

driving said second conductor to a high state, and

determining whether the signal on said first conductor transitions high in response to said driving;

(b) driving said clock signal onto said second conductor;

(c) issuing signals representative of said data onto said first conductor;

(d) stopping said driving said clock signal onto said second conductor; and

(e) pausing for a predetermined period of time.

20. A method for transferring data serially between a computer system and a power source using a first conductor and a second conductor, said first conductor having a first portion and a second portion removably connected by a first connector, said second conductor having a third portion and a fourth portion removably connected by a second connector, said computer system being coupled to said first portion and said third portion, said power source being coupled to said second portion and said fourth portion, said first conductor for transferring said data and said second conductor for transferring a clock signal, said method comprising the steps of:

(a) synchronizing said power source to said computer system, said synchronizing including,

determining automatically whether the signal on said first conductor is pulled to a first state or a second state,

determining automatically whether the signal on said second conductor is pulled to the first state or the second state,

determining both that said first portion and said second portion are not coupled together and that said third portion and said fourth portion are not coupled together in response to both said signal on said first conductor being in said first state and said signal on said second conductor being in said second state, otherwise,

re-charging said power source;

determining whether the signal on said second conductor transitions from a high state to a low state,

driving said first conductor to a low state, and

determining whether the signal on said second conductor transitioned from a low state to a high state;

(b) issuing signals representative of said data onto said first conductor for a period of time; and

(c) setting an interrupt bit upon completion of said issuing of said signals.

21. The method as defined in claim 20, wherein said step (c) comprises repeating steps (a) and (b) if said interrupt bit is not set within a predetermined amount of time.

22. The method as defined in claim 20, further comprising the step of storing said data in a storage device.

23. The method as defined in claim 20, further comprising the step of preparing said power source for a subsequent data transfer.

24. The method as defined in claim 20, further comprising repeating steps (a) through (c) for a subsequent data transfer.

25. The method as defined in claim 20, further comprising the step of determining whether said computer system is receiving data or sending data.

26. The method as defined in claim 25, further comprising the step of storing the data to be transferred into a data register if said computer system is sending data and storing a value of FF₁₆ into said data register if said computer system is receiving data.

27. A system for communicating information between a computer system and a power source, the system comprising:

a first signal conveyance medium for transferring a clock signal from the computer system to the power source, the first signal conveyance medium including a first portion removably coupled to a second portion, and circuitry for automatically pulling the first signal conveyance medium to a first predetermined state when the first portion is coupled to the second portion and for automatically pulling the first signal conveyance medium to a second predetermined state when the first portion is not coupled to the second portion;

a second signal conveyance medium supporting serial communication between the computer system and the power source;

wherein the computer system is coupled to the first portion of the first signal conveyance medium and the second signal conveyance medium, and wherein the computer system is configured to detect whether the power source is coupled to the computer system based on whether the first signal conveyance medium is pulled to the first predetermined state;

wherein the power source is coupled to the second portion of the first signal conveyance medium and the second signal conveyance medium, and wherein the power source includes an input port for retrieving first data from the second signal conveyance medium, and an output port for placing second data on the second signal conveyance medium; and

a circuit, coupled to the second signal conveyance medium and the output port, which allows the input port and the output port to alternately share the second signal conveyance medium to support serial communication with the computer system.