A method and apparatus for interfacing an electronic device with an external accessory

METHOD AND APPARATUS FOR BINDING AN ELECTRONIC DEVICE TO AN EXTERNAL ACCESSORY

BACKGROUND

This invention relates generally to the field of electronic devices relating to an accessory control bus interface and more particularly to a method and apparatus for operating such devices with external accessories, including accessories that do not include compatible bus interfaces.

In order to add additional features and functions, many consumer, teleCommunication and industrial electronic devices 10 are coupled to external peripherals through suitable accessory gates. When the accessory and the electronic device are connected, their auxiliary accessory connectors attempt to mode their respective electrical connections to the accessory signals. For example, a portable cordless phone can be paired with a properly formatted handsfree external accessory holder, making it easier to operate the phone in a car. Typically, a car handsfree device includes an audio circuitry to amplify the sound in the car and another circuitry to control the audio signals from the car to the phone. Another version of the external handsfree is a less cumbersome portable handsfree that includes a small earpiece and a microphone. When the wearer is wearing a portable handsfree, the earpiece and microphone are respectively located near the mouth of the wearer. In this way, the portable handsfree allows the user to operate the phone without holding it. Another popular accessory is the battery charger, which can be paired with a car handsfree device to charge the phone battery.

If the device is running on an external accessory, it may be necessary for the electronic device to adjust its performance. For example, when working with a portable handsfree, the phone increases its audio output power, which is directed to the accessory port to accommodate the portable handsfree. Consequently, most electronic devices are equipped with a sensitivity scheme that recognizes the presence or absence of an external accessory.

Many conventional electronic device sensitivity schemes recognize the predetermined electrical conditions created for the accessory port where the external accessory is located. Some external accessories present a predefined binary state (high or low) to indicate their presence. Alternatively, the accessories may provide an electrical parameter on the accessory gate, such as an impedance, which allows different types of accessories to be distinguished. Recognizing a particular obstacle, which may be represented by a voltage potential accessory gate, the electronic device may determine the type of connected external accessory.

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As technology advances, electronic devices and their accessories become more and more sophisticated. Often more sophisticated electronic devices include intelligent microcontrollers to control various functions, such as controlling screens and input / output gates, etc. To keep up with these developments, manufacturers are also supplying external peripherals with intelligent controllers. Consequently, it is necessary to communicate through the operating parameters between several electronic devices and their external accessories. In these cases, the operation of the electronic device and the external accessory may require repeated exchange of one or more dynamically changing operating parameter information on which the operation of the electronic device and / or accessory is adjusted to achieve or improve the operation of a particular function. For example, when moving from one communication line to another, the phone may send an external handset accessory handover parameter along with audio parameters corresponding to the working environment of the new cell. By taking into account the performance of the new cell, the car handsfree device can adjust the parameters of its echo cancellation scheme to provide better audio quality inside the car.

Some sophisticated electronic devices and accessories use the Accessory Control Bus (ACB) to send operating parameters to each other. One such ACB interface is I²C bus interface developed by Philips Corporation. I²The specification and scheme of action of the C bus interface are described in detail in Philips Semiconductors The I²C-bus and how to use it (including specifications), April 1995, incorporated herein by reference. ACB equipment incorporating I²C interface, can send a wide range of complex operating parameters over double row sequential bus speeds up to 400 kbit / s.

However, it is often necessary to enable collaboration between ACB devices and non-ACB devices. For example, an ACB device equipped with an I²C bus interface, sometimes has to work with a simple non-ACB accessory that does not include I²Interface C. Conversely, an ACB accessory equipped with I²C function, must work with non-ACB device. Typically, inter-device solutions involve complex modifications of ACB devices or non-ACB devices. These modifications often increase the cost of achieving compatibility. Therefore, there is a need for a simple method and apparatus for combining ACB and non-ACB devices.

EXECUTIVE SUMMARY

Briefly, the present invention, which addresses this need, has been implemented in an electronic device and method of operation, wherein the electronic device changes the interface mode of the electronic device based on the interface of the connected external accessory.

EE 199900512 Α type. The electronic device has a gateway for connection to an external accessory through an interface bus and a bus interface that creates data exchange over the interface bus. The controller controls the operation of the electronic device in the first interface mode when a communication link is established with the external device, or in the second interface mode when the communication device is not connected to the external device. In the first interface mode, the electronic device and the external device may send at least one operating parameter information over the interface bus, and in the second interface mode, operating parameters may not be transmitted over the interface bus. In this case, the electronic device may use the default default operating parameter when operating in another interface mode.

In some exemplary states of the invention, the bus control interface creates an interface bus over rigid links and detects a transition from the first binary state to the second binary state to determine if a data link is established. If no transition is detected within the designated time period, the electronic device concludes that no data exchange was performed. In another aspect of the invention, the bus control interface establishes a data communication connection in response to a signal transfer on a gate when an external device is connected to an electronic device.

In yet another aspect of the invention, the bus interface establishes data exchange using at least two different data rates and determines whether data exchange is established at each different data rate. The controller may also control an electronic device in the first interface mode to transmit a predetermined operating parameter over the interface bus. It then controls the electronic device's second interface mode, where no operating parameter is transmitted.

The method of operating an electronic device according to the present invention comprises initiating data communication with an external device through a gate. It then determines whether data exchange with the external device is established. Once the data exchange has been established, transmission of the operating parameter between the electronic device and the external device is negotiated. Otherwise, not sending the operating parameter between the electronic device and the external device.

Other features and advantages of the present invention will be apparent from the following description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.

DESCRIPTION OF THE SHORT DRAWINGS

FIG. 1 is a diagram of an electronic device and various accessories that may work with an electronic device in accordance with the present invention.

Figure 2 is a block diagram of the telephone of Figure 1 and external peripherals.

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Figure 3 is a flowchart of the steps taken in accordance with the present invention to operate the electronic device with external peripherals.

DETAILED DESCRIPTION

Referring to Figure 1, a cellular telephone 10 is illustrated as an example of an electronic device operating in accordance with the present invention. At the bottom, the phone includes an accessory interface 10 for connecting 12 different types of external accessories according to the present invention. The telephone 10 operates in a well known manner in a mobile communication system to provide two-way voice and data communication within the coverage area. The sample telephone 10, which may usefully include a method and apparatus for working with an external accessory in accordance with the present invention, is an AF-738 or GF-788 cellular telephone provided by Telefonaktiebolaget LM Ericsson, the applicant of the present invention. The accessory interface 12 includes a plurality of accessory contact terminals 14 and a spring locking socket 15. The contacts 14 and latches 15 are associated with respective external accessory contact terminals and locks when the accessory is connected to a telephone. When the telephone 10 is connected and connected to an external accessory, they communicate with one another via the accessory interface 12. The required accessory signals, including audio signals, serial data gateway signals, control signals, power contacts, and analogue and digital grounding available at the respective accessory contacts are interconnected.

In this exemplary embodiment, the telephone is an ACB device comprising an ACB interface implemented in accordance with I²C bus interface. According to I²C bus interface specification, this bus can be backed by hardware or software. In a hardware solution, a single integrated circuit performs gate functions, including data exchange, evaluation, clock generation, addressing, and so on. In a software solution, the microcontroller, which is also responsible for controlling other phone functions, executes

ACB features. The microcontroller performs these functions by running a suitable gate program. Considering the above, the data rate over the ACB interface is slower for the software solution than for the hardware solution. Hereinafter, devices that include a hardware solution for the ACB interface are referred to as high-speed ACB devices and those that include a software ACB interface solution are referred to as slow ACB devices. Devices that do not have an ACB interface are called non-ACB devices.

As will be described in more detail below, in an exemplary embodiment, the phone may be either a slow ACB device or a fast ACB device. However, the method and apparatus of the present invention are equally applicable to the interaction of an electronic device with an external device when the telephone is a non-ACB device that works with an ACB external accessory. According to the present invention,

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The ACB device, which may be a telephone, a slow ACB external accessory, or a high-speed ACB external accessory, establishes data exchange through the accessory gate interface bus. When data communication with an external device is established, the ACB device operates in the ACB bus interface mode, where at least one operating parameter is transmitted from the ACB device over the interface bus. The ACB interface mode can be fast ACB interface mode or slow ACB interface mode. However, if no data exchange is established, the ACB device will operate in non-ACB device interface mode, where operating parameters will not be transmitted from the ACB device over the bus. This situation occurs when an ACB device is used with a non-ACB device. By switching the interface mode according to whether bus communication was established, the ACB device operating in accordance with the present invention is compatible with high-speed ACB, slow ACB, and non-ACB devices without the need for any sophisticated interface modifications such as those required by conventional mating methods.

As shown in Figure 1, there are four types of accessories that can be connected to the phone via the accessory gate. These accessories include high-speed ACB external accessory 16, slow-ACB external accessory 18, non-ACB external accessory 20, and quasi-ACB external accessory 22. The quasi-ACB external accessory 22 operates in quasi-ACB interface mode. In Quasi-ACB interface mode, the external accessory operates with limited ACB functionality that allows one or more predetermined operating parameters to be transmitted to or from the ACB device during the initial boot period of the interface bus. Subsequently, when the data transfer is complete, the quasi-ACB accessory operates in non-ACB device interface mode, where operating parameters are not transmitted over the bus. External accessories operating in this way in quasi-ACB interface mode can be manufactured more easily without the cost and complexity of a full ACB interface functionality.

Referring to Figure 2, a block diagram is provided showing the telephone 10 and various external accessories that may be connected to the telephone 10 to the extent necessary to understand the present invention. Through the accessory interface 12, the telephone communicates with one or more external accessory devices including a high-speed ACB accessory 16, a slow ACB accessory 18, a non-ACB accessory 20 and a quasi-ACB accessory 22. All electrical connections to the phone 10 and accessory 16. Between 18, 20 and 22, this is accomplished through an accessory interface 12. In the exemplary embodiment, the interface 12 of the accessory includes eleven contact terminals

14 which ensure the accessory input or output signals are received from or to the telephone

10th Table 1 below identifies the auxiliary signal functions for each accessory terminal 14 in the default interface configuration. Table 1 also determines whether the auxiliary signals are input, output or input / output signals.

According to Table 1, the input signals (denoted by I) are directed to the telephone 10 and

EE 199900512 Α Output signals (marked with 0) are outward from the phone. Two-way signals are denoted as I / O signals.

Table 1

<td>The terminal</td><td>Signal</td><td>Function</td><td>I / O</td>

<td>^! 1</td><td>AFP</td><td>audio from your phone</td><td> 0</td>

<td> 2</td><td>ATP</td><td>audio phone</td><td>I</td>

<td>³</td><td>SCL</td><td>consecutive tactics</td><td>I / O</td>

<td> 4</td><td>AGND</td><td>audio signal ground</td><td> -</td>

<td>⁵</td><td>SDL</td><td>sequential data line</td><td>I / O</td>

<td> 6</td><td>V FLASH</td><td>flash memory voltage</td><td>I</td>

<td> 7</td><td>VDD</td><td>logical level. Status ON</td><td> 0</td>

<td> 8</td><td>DFP</td><td>data from your phone</td><td> 0</td>

<td> 9</td><td>DGNG</td><td>digital signal grounding and dc rebound</td><td> -</td>

<td> 10</td><td>DTP</td><td>data on your phone</td><td>I</td>

<td> 11</td><td>DCIO</td><td>DC + pole to charge the phone battery, and to power the accessory</td><td>I / O</td>

As mentioned above, in exemplary embodiments of the present invention, the ACB interface is I²Interface C. I²Interface C defines bidirectional communication over two-line serial bus 25. The physical configuration of the interface bus 25, which is located in the accessory interface 12, includes two open collector bus lines. These bus lines are a serial data line (SDL) and a sequential tact line (SCL) at terminals 3 and 5, respectively.

The IC bus interface provides access to a plurality of addressable devices that operate as master or slave and are connected to the interface bus. According to the protocol, the control unit is responsible for initiating data exchange over the interface bus 25 and generates clock signals that enable such data exchange. By switching multiple ACB accessories to bus 25, the phone can communicate with many devices in master-controlled mode. During the data exchange, all devices addressed to the driver are considered to be controllable. The driver is also responsible for completing the data exchange. The driver initiates data exchange over bus 25, creating a START state, and interrupts data exchange, creating a STOP state. The START state is created by switching from a high binary state to a low binary state on the SDL line at terminal 5,

EE 199900512 Α while the SCL line is kept in high binary state. The STOP state is created by switching from a low binary state to a high binary state on the SDL line, while the SCL line is maintained in a high binary state. As will be described later, the controlled device may also generate a START state which acts as an interruption to the control device.

Exchange of data²The C bus can be in bit-by-bit or byte-byte formats. For each broadcast format, I determines²Protocol C Procedures for synchronizing the clock clock and evaluating the bus. The control unit can start data exchange only if it is free here. By following the procedures described in the protocol, two or more controls can mediate bus access. Once granted, digital information can be transmitted over the bus at 100 kbit / s (or 400 kbit / s in high-speed mode), provided the bus capacity does not exceed 400pF. By using the clock frequency synchronization mechanism for bit-by-bit data exchange, the device can downlink the data rate on the bus. By expanding each clock during low binary state, the device connected to the bus can adjust its data rate accordingly. In this way I²The C protocol allows faster devices to communicate with slower devices across the interface bus 25.

In one embodiment of the present invention, the telephone 10 is a high-speed ACB device comprising a dedicated bus interface integrated with a microcircuit 24 for performing ACB interface functions. One such integrated circuit is I²C bus device from Philips Corporation that includes bus interface features such as START status and

Detecting the STOP status in the chip configuration of the bus interface.

In another embodiment, the telephone 10 is a slow ACB device that performs ACB interface functions through an interface software executed by microcontroller 26. In Figure 2, the interface software is shown as a dotted box inside microcontroller 26. In such an arrangement, microcontroller 26 itself performs ACB functions, including sampling the binary states of the SDL and SCL lines to determine START and STOP conditions. Because of the burden associated with implementing the ACB interface functions, a slow ACB phone transmits information at a lower rate than a fast ACB phone's transmission speed. It has been determined that a slow ACB phone can send information at a rate of about 100 bit / s over an interface bus.

In both cases, in the high-speed ACB and slow-ACB phones, microcontroller 26 is programmed to control the overall operation of the telephone 10, including the radio unit 28, audio unit 30, power supply unit 32, and serial interface interface unit 34. As is well known, radio unit 28 is responsible for wirelessly transmitting voice and information messages over designated radio frequency channels as well as for receiving such messages.

The audio unit 30 is responsible for processing the audio signals, including voice messages

EE 199900512 Α encoding and decoding. The audio unit 30 receives the accessory signal from the audio accessory (ATP) to the external accessory terminal 1 and outputs the accessory signal from the audio phone (AFP) to the external accessory terminal 2. The power supply 32 controls the power supply to operate the telephone For example, the phone 10 may be powered internally by a battery or externally by a car handsfree device which may also be responsible for charging the battery. Power supply 32 receives an external source signal, including a battery charger, through DCIO accessory terminal 11. Alternatively, power supply 32 can supply power to the external accessory via the same accessory signal. Power supply 32 also provides a regulated reference voltage at VDD accessory terminal 7, which, among other things, signals whether the phone is on or not. Information via telephone (DTP) signal at accessory terminal 10 and information from telephone (DFP) at accessory terminal 8, serial bus interface unit 34 allows the telephone to communicate with the information terminal directly or via a modem. Analog Grounding (AGND) and Digital Grounding (DGND) at accessory terminals 4 and 9 provide an audio and digital grounding connection between the telephone and external accessories. The VFLASH signal at terminal 6 allows the external device to update the flash memory, which stores the work programs of the microcontroller 26 in a known manner.

Similarly to the high-speed ACB phone, the high-speed ACB external accessory 16 includes a dedicated ACB interface chip 36 to connect it to the telephone 10 through the accessory interface 12. As noted above, the high-speed ACB accessory 16 can transmit information at speeds up to 10 kbit / s. However, if the telephone 10 associated with the fast ACB external accessory is a slow ACB device, the data rate is limited to the slow ACB device speed. The high-speed ACB accessory 16, which may, for example, be an intelligent car handsfree accessory, also includes an accessory controller 38 for general control of the accessory operation. Through a suitable circuit arrangement, the accessory function block 40, which operates under the control of the accessory controller 38, performs all the functions of the accessory. In the case of an auto handsfree device, the accessory function block 40, for example, includes an audio circuitry for amplifying AFP and ATP accessory signals and supplying power to the phone from terminal 11. The accessory controller 38 controls a designated ACB interface chip 36 to operate between

Like the slow ACB phone 10, the slow ACB accessory 18 implements the functions of the ACB interface by running the bus interface software. The bus interface software, shown as a dotted box, is executed by the slow ACB accessory controller 42 which controls the overall operation of the accessory 18. Through the accessory controller 42, the operating parameters can be transmitted between the telephone 10 and the slow ACB external accessory 18 at a rate of about 100 bit / s.

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In the exemplary embodiment, the slow ACB external accessory 18 may be a simpler car hansfree accessory. By not relying on well-targeted hardware, this simpler handsfree enhancement can be produced at a lower cost. Like the high speed ACB external accessory 16, the slow ACB accessory 18 includes an accessory function block 44 which, under the control of the accessory controller 42, performs the specific functions of the accessory associated with the device.

The non-ACB external accessory 20, which may be a simple portable handsfree accessory, does not include any ACB functionality. The non-ACB external accessory 20 includes one or more grounded resistors 46 which, in conjunction with the accessory interface, pull down open collector terminals to provide low binary status on one or both of the SDL and SCL lines at terminals 3 and 4 of the accessory interface 12. As will be described in more detail below, in response to the low binary state on the accessory interface, the telephone 10 can detect the presence of a non-ACB external accessory 20. The accessory features and functionality of the non-ACB accessory are implemented with the corresponding schema solution in the non-ACB accessory functional block 48. As an example of a simple portable handsfree device, the non-ACB accessory function block may include a simple audio circuitry, such as a small earpiece and a microphone, that send and receive audio signals through ATP and AFP accessory signals from terminals 1 and 2 at accessory interface 12.

Finally, Figure 2 shows a block diagram of a quasi-ACB accessory 22. As mentioned above, the quasi-ACB external accessory 22 implements only limited functionality of the ACB accessory. After the initial phase, the quasi-ACB interface 50 performs limited ACB interface functions during the initial start-up period. The limited functions performed by the quasi-ACB interface 50 include clock frequency synchronization and limited data exchange functions. The accessory function block 52 includes a functional diagram of the quasi-ACB external accessory 22.

During the initial start-up period, a predetermined set of operating parameters is transmitted between the telephone 10 and the quasi-ACB external accessory 22 over the interface bus. Once such data transfer is complete, the quasi-ACB accessory 22 enters a non-ACB interface mode where no operating parameters are transmitted between the telephone 10 and the quasi-ACB accessory on a single interface bus. If the device to be connected to the quasi-ACB accessory is a non-ACB device, the predefined operating parameters sent to the bus are ignored. Otherwise, the quasi-ACB external accessory 22 sends the predetermined operating parameters to the ACB device or to the ACB device associated with the accessory.

A sample quasi-ACB accessory may be a hands-free accessory that, during the startup period, transmits parameters related to its audio functionality to the phone 10.

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The accessory then functions as a non-ACB accessory without the ability to send operating parameters to the phone 10. Through external mode setting means such as the mode switch 54, the quasiACB external accessory 22 can be reset to operate in ACB interface mode when attempting to initiate communication with the phone over the interface bus. 25th

Functionally, the telephone 10 may be coupled to any high-speed ACB, slow ACB, quasi-ACB, and non-ACB external accessory 16, 18, 20, and 22 through the attachment through the accessory interface 12. External accessories are generally connected to the phone on any surface. The telephone 10 can be coupled to accessories either as a driver or as a driver. Acting as a driver, the phone is forced to perform periodic assessments on the interface bus to detect the presence or absence of an accessory. Such an evaluation function on a fixed periodic surface increases the above with respect to the attachments to the accessories. As described above, as a driver, the processing power of the microcontroller 26 in the telephone 10, which controls many other functions, may be limited. Therefore, in a preferred embodiment of the invention, the external peripherals of the ACB act as drivers that initiate data transfer over the interface bus. As will be described in more detail below, the telephone 10 acts as a conductor when the accessory interface 12 has a low binary state due to connection to the non-ACB accessory 20.

When the high-speed ACB external accessory 16, which acts as a driver in the initial high-speed ACB mode, is connected to the telephone 10, it initiates data exchange over the interface bus according to I²C protocol at the original high speed. Following the clock frequency of the synchronization process, which

I²As interface C established, the external accessory can determine whether or not the phone is connected. If the telephone 10 is a fast ACB device, the SCL signals are synchronized quickly. In this situation, data exchange is established almost immediately and the telephone 10 and the external accessory 16 both operate in high-speed ACB interface mode. In high-speed ACB interface mode, one or more operating parameters are transmitted between the telephone 10 and the high-speed ACB accessory 16 over the interface bus 25 at high data rate. If the telephone 10 is a slow ACB device, the attempts of the high speed ACB external accessory 16 to establish high speed data exchange have failed. In this case, the slow ACB telephone 10 extends the low bin state clock signal according to I²C protocol to download the data rate of high-speed ACB external accessory 16 over interface bus 25. When communication is established at lower speeds, the telephone 10 and external accessory 16 operate in slow ACB interface mode where operating parameters are transmitted over the interface bus at approximately 100 bit / s. .

Similarly, the slow ACB external accessory 18 connects to either the fast ACB phone or the slow ACB phone as a driver. By connecting to a high-speed ACB phone, the low-speed ACB external accessory 16 generates a lower-frequency clock frequency, operating at its low-speed

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In interface mode, the phone 10 applies the higher interface speed to the external accessory 18 at a lower interface speed, extending the low binary state on the SCL line. When connected to a slow ACB phone, the external accessory and the clock frequency generated by the phone are virtually identical, so that the exchange of data between them is almost immediate. Once the data exchange is established with a high-speed ACB phone or a slow ACB phone, the low-speed ACB external accessory 16 and the phone 10 operate in slow-ACB interface mode. In this mode, operating parameters are transmitted at 100 bit / s. Although the control unit is responsible for detecting devices connected to the bus, the controlled device may initiate the connection by establishing START conditions on the bus. The START conditions are for the control unit to be interrupted to service the service request from the controlled device.

When the non-ACB external accessory 20 is connected to the telephone 10, the pull-down resistors 46 ground the open collector terminator to one or both of the terminals 3 and 5. In response to low binary status at one or both of these accessory terminals, the telephone 10 acts as a control unit. The telephone 10 recognizes the SCL line at terminal 3 of the accessory interface, which is pulled down to a low binary state by a non-ACB external accessory for a predetermined period of time. If the telephone 10 does not detect a low-to-high transition on the SCL line for a designated time period, it will enter a non-ACB interface mode. In non-ACB mode, operating parameters are not sent to or from the phone 10 over the interface bus. Instead, the phone may use preprogrammed default parameters to connect to a non-ACB accessory. For example, if the non-ACB accessory is a simple portable handsfree external accessory, the phone will use the original operating parameters, such as the attenuation and gain parameters AFP and ATP output, or input signals at the accessory terminal 1 and 2.

While the telephone 10 operates on the quasi-ACB external accessory 22, the quasi-ACB external accessory 22 initially operates in the ACB interface mode, which may be either a fast ACB or a slow ACB interface. In such an arrangement, the quasi-ACB accessory 22 acts as a control to establish data exchange with the telephone during the initial period. Once established, the quasi-ACB external accessory 22 sends a predetermined set of operating parameters to or from the telephone 10. When the data exchange is completed according to²To the C interface, the quasi-ACB external accessory 22 enters a non-ACB interface mode where no operating parameters are transmitted between the external accessory 20 and the telephone 10.

Figure 3 illustrates a flowchart of the steps performed when a telephone 10 is operated with various types of external accessories in accordance with the present invention. Originally an ACB device, which can be either a phone 10, a fast ACB or a slow ACB external accessory 16, 18, 20,

EE 199900512 Α or 22, initiates communication through the auxiliary interface 12 over the interface bus 25 according to the first initial ACB mode, block 310. A decision is then made as to whether or not to initiate data exchange, block 320. The decision is made by examining the SCL line on the accessory interface 12 for a predetermined . If the connection is established during the assignment period, the ACB device operates in a first ACB interface mode where one or more operating parameters are transmitted over the interface bus 25 at the first data rate, block 330. However, if no communication is established, the ACB device attempts to establish communication over the bus 25 in the second ACB mode. block 340. A decision is made as to whether the data exchange was created in another ACB mode, block 350. When the data exchange is established, the ACB device operates in another ACB mode where the operating parameters are transmitted at the second data rate, block 360. If the data exchange is not established in the second ACB mode, the ACB device operates in non-ACB interface mode unless the operating parameters are transmitted over the interface bus. If no operating parameters are sent, the ACB unit may use the original default operating parameters. As described above, establishing a data exchange involves initiating a connection using at least two data rates.

It will be apparent from the foregoing description that the present invention provides a simple method and apparatus for cooperating with an electronic device and an external accessory. The present invention directs ACBs to operate in ACB mode if data transfer attempts over the interface bus are successful. In this way, the present invention provides a cost effective method and apparatus for coupling sophisticated accessories and simple accessories to electronic devices without significant costly and complicated modifications.

Although the invention has been described in detail only with reference to a preferred embodiment, those skilled in the art will appreciate that various modifications can be made without departing from the spirit of the invention. Consequently, the invention is defined only by the following claims, which should therefore include all equivalents.