GB2389429A

GB2389429A - Electronic accessory detection and identification

Info

Publication number: GB2389429A
Application number: GB0214111A
Authority: GB
Inventors: Kirem Dominic Rahmani
Original assignee: Sendo International Ltd
Current assignee: Sendo International Ltd
Priority date: 2002-05-28
Filing date: 2002-06-20
Publication date: 2003-12-10
Anticipated expiration: 2022-06-20
Also published as: GB0212262D0; GB0214111D0; GB2389429B

Abstract

A device 11, such as a mobile telephone, has a connector 12 for receiving an accessory 50. When the accessory is connected, a voltage change occurs at a pin 14, generating an interrupt signal EXT-nINT, and activating a voltage regulator 30 to power the accessory 50 at a terminal 32. The voltage produced at pin 14 is processed 40, 60 and used to identify the accessory 50 which has been connected.

Description

1 1 - 1 ACCESSORY DETECTION AND IDENTIFICATION

Field of the Invention

5 The present invention relates to a method and apparatus for the detection and identification of accessories, in particular to the detection and identification of accessories on connection of the accessories to an electronic device.

Background of the Invention

! Electronic devices, and in particular mobile i, communications devices, are becoming more and more 15 sophisticated, and being provided with more and more features and functionality. Because of this, the range of .. accessories that can be connected to an electronic device is also increasing.

; 20 A known problem in the field of the present invention is..DTD: the ability of the electronic device to be able to detect when an accessory has been connected to the device.

Furthermore, the electronic device often needs to identify at least the type of accessory that has been 25 connected so that the electronic device can operate and/or interact with the accessory accordingly.

A known method of 'identifying' an accessory connected to an electronic device is to provide an identification pin.

30 When the accessory is connected, the signal provided by

- 2 - the accessory on the identification pin provides an indication of at least the type of accessory connected.

For example, a resistor is provided within the accessory, 5 and connected between the identification pin and ground.

On connection to the electronic device, the resistor provided within the accessory forms part of a potential divider circuit, the remainder of the potential divider circuit being provided by the electronic device. The 10 electronic device provides a voltage to the potential divider circuit, and measures the resulting voltage at the identification pin.

! Hence, by providing for different values of the resistor .. 15 within different accessories, the voltage measured at the identification pin may identify a type of accessory.

Therefore, a different value resistance can be used for different accessories, and each accessory can be . identified by a distinct voltage value that is measured .... À 20 at the identification pin.

However, in processor-driven devices, it is generally necessary for the electronic device to be able to detect when an accessory has been connected. One known method is 25 to provide an interrupt pin. When an accessory is connected to the device, an interrupt signal is sent from the interrupt pin to, for example, a processor of the electronic device, informing the electronic device that an accessory has been connected thereto.

This method suffers from the disadvantage that an interrupt pin, in addition to an identification pin, is required as part of the connector with which the accessory is able to connect to the electronic device.

5 This increases the cost of the connector, and the size of the connector, both of which are important restrictions on devices such as mobile communications devices.

Another known method of detecting when an accessory has 10 been connected to an electronic device, which does not require the extra pin, is for the electronic device to periodically measure the voltage at the identification , pin. When a measured voltage corresponds to a distinct . voltage of an accessory, it assumes that the accessory is 15 connected.

This method suffers from the disadvantage that, even when an accessory is not connected, processing time is . .' ' required to poll for the accessory, thereby reducing the ''' 20 efficiency of the electronic device. Furthermore, depending on the frequency at which the electronic device polls for an accessory, there will generally be a delay between the accessory being connected and the electronic device detecting the accessory. By increasing the 25 frequency at which the electronic device poles this delay can be reduced. However, this will increase the processing time required to pole for the accessory...DTD: In summary, a circuit designer, when attempting to design

30 a detection and identification mechanism for accessory connections, is presently confronted with the options of:

- (i) Employing two dedicated pins (an identification pin and an interrupt pin) on the interface connector, or (ii) Employing a processor polling technique that 5 consumes processing time and power and includes an inherent delay in the detection and identification process. Therefore, a need has arisen for an improved accessory 10 detection and identification mechanism, wherein the aforementioned disadvantages with prior art mechanisms

are substantially alleviated.

Statement of Invention

According to a first aspect of the present invention .. there is provided, an electronic device, according to Claim 1.

20 According to a second aspect of the present invention there is provided, a method of detecting and identifying an accessory connected to an electronic device, according to Claim 5.

25 Thus, according to the preferred embodiment of the present invention, a (status) voltage change at the identification pin of the electronic device is used to detect (by generating an interrupt signal) and identify the accessory. In this way, only a single pin is required 30 for both the detection and identification of the accessory. Furthermore, since the change in voltage

caused by connection of the accessory generates the interrupt signal used for detecting the accessory, there is no need for a processor to poll the accessory.

5 Thus, the problems identified in the background of the

invention are substantially alleviated.

Brief Description of the Drawings

0 Exemplary embodiments of the present invention will now be described, with reference to the accompanying drawings, in which: , . FIG. l and FIG. 2 illustrate detection and identification ., 15 circuitry according to a preferred embodiment of the present invention.

:' FIG. 3 illustrates a flow chart of a method of detecting and identifying an accessory connected to an electronic And 20 device according to the present invention.

Description of Preferred Embodiments

Referring to FIG. l there is illustrated an accessory 25 detection and identification circuitry lo according to the present invention. The circuitry is suitable for use in an electronic device ll such as a mobile communications device, and is coupled to a connector 12 to which an accessory is capable of being connected.

- 6 For the particular illustration of FIG. 1, the circuitry 10 has been illustrated with no accessory connected thereto. 5 The circuitry lO comprises an identification pin 14, which when no accessory is connected to the electronic device 11 has a first open voltage.

For the illustrated embodiment, the identification pin 14 10 is part of a connector 12, to which an accessory can be connected. A voltage supply VIO is connected to the identification pin 14 via a resistor R1. In this way, when no accessory is connected to the connector 12, i.e. . when the identification pin 14 provides a substantially 15 open circuit, the potential difference between identification pin 14 and ground (VID) is substantially .. equal to VIO. Therefore, for the illustrated embodiment, :' the open voltage of the identification pin 14 is VIO.

. 20 For the illustrated embodiment, the connector 12 further comprises a ground pin 18, the ground pin 18 being connected directly to the ground plane of the electronic device 11...DTD: 25 The circuitry 10 further comprises an interrupt generation mechanism, which generates an interrupt signal (EXT_nINT) in response to a change in voltage at the identification pin 14. Such a change in voltage is caused by the connection of an accessory to the device 30 11.

- 7 For the illustrated embodiment, the interrupt generation mechanism comprises a AMOS transistor 16. The identification pin 14 is connected to the gate of the PMOS transistor 16. The voltage VIO is provided to the 5 source of the transistor, whilst the drain of the transistor is connected to ground via a resistor R2. When the voltage across the gate and source of the transistor 16 (Vgs) is below a threshold value (which for this particular implementation is negative), the transistor 16 10 will allow current to flow there through. However, when the Vgs is above the threshold, the transistor 16 substantially prevents current from flowing there through. . .. I 15 The voltage subsequently provided at the drain of the transistor 16 is used to provide the interrupt signal .. EXT nINT. The voltage is provided to an analogue to . _ digital converter (ADC) 40 that generates, as an output, the interrupt signal EXT_nINT. This interrupt signal is , 20 forwarded to, and used by, for example, processor 60 within the electronic device 11 to indicate when an accessory has been connected to the connector 12.

In this manner, a change of voltage in the single 25 identification pin 14 is used to generate an interrupt signal that is input to processor 60. This arrangement advantageously avoids the need for the processor to poll the identification pin 19 and avoids the need to have a separate interrupt pin provided on the connector 12.

- 8 - As will be appreciated for the illustrated embodiment, when no accessory is present and the identification pin 14 provides a substantially open circuit, the voltage at the identification pin 14 is substantially equal to VIO.

5 This VIO voltage results from there being substantially no current flowing through resistor R1. The voltage at the gate of the transistor 16 will also be substantially VIO. Hence, the voltage across the gate and source (Vgs) of the transistor 16 is substantially zero, which is 10 above the threshold voltage. Therefore, the transistor 16 substantially prevents current flowing there through.

Therefore, the interrupt signal is pulled low, due to the resistor R2 connecting it to ground, indicating that no .. accessory is present.

1' 15 The present invention is not limited to the use of a .. transistor to provide the interrupt generating mechanism, .. and in particular the invention is not limited to the use of the PROS transistor 16 of the illustrated embodiment...DTD: 20 Any suitable type of transistor could be used, or even an amplifier. Indeed, it is envisaged that any component/ mechanism that is capable of detecting the voltage change, and producing a logical state change for the interrupt, can be used. The only requirement is that the 25 interrupt generating mechanism should be simple, small and relatively inexpensive.

The circuitry 10 also comprises a voltage indication mechanism, which for the illustrated embodiment is in the 30 form of an analogue to digital converter (ADC) 40, which is connected to the identification pin 14. The voltage

- 9 indication mechanism, or ADC 40, has as an input the voltage at the identification pin 14, and has as an output an indication of the voltage, which is provided to, for example, the processor 60. It is within the 5 contemplation of the invention that the ADC 40 may be an integral part of the processor. Thus, for the illustrated embodiment, the ADC 40 takes the voltage at the identification pin 14, which is an analogue signal, and converts it into a digital representation thereof. The 10 use of this voltage indication at the identification pin 14 will be described in more detail below.

It will be appreciated that the present invention is not . ! limited to the use of an analogue to digital converter . 15 for the voltage indication means, and that any suitable alternative may be used.

Referring now to FIG. 2, there is illustrated the accessory detection and identification circuitry 10 of 20 FIG. 1, in accordance with an enhanced embodiment of the . present invention. Also illustrated is a resistor Racc 52 forming part of an accessory 50 connected to the electronic device 11 by way of the connector 12.

25 When the accessory 50 is connected to the electronic device 11 in this way, the resistor Racc 52 is connected across the identification pin 14 and the ground pin 18.

In this way, the voltage at the identification pin 14 is pulled down below the value of VIO.

- 10 The value of the resistors R1 and Racc are such that the resulting voltage at the identification pin 14, when the accessory is connected thereto, is low enough to make the voltage across the gate and source (Vgs) of the 5 transistor 16 less than the threshold value. In this way, the transistor allows current to flow there through, raising the voltage across the resistor R2 to substantially equal to VIO.

10 Thus, the signal EXT_nINT is now high, generating an interrupt signal that informs the processor 60 that an accessory has been connected to the electronic device 11.

. ,' On receipt of the interrupt signal, and thereby detection 15 of the accessory, the processor 60 obtains the indication of the voltage at the identification pin 14 from the ADC .. 40, and uses it to identify the accessory.

For example, a lookup table may be stored in an area of 20 memory 70, which can be retrieved by the processor 60.

The processor 60 compares the voltage indication of the voltage at the identification pin 14 with the lookup -

table. On locating a comparable entry in the lookup table, the processor 60 identifies at least the type of 25 accessory connected, and initiates appropriate actions for that accessory.

By using different values of the resistor Racc 52 within different accessories, the voltage measured at the 30 identification pin 14 will identify the different accessories connected to the electronic device 11.

Therefore, each accessory 50 can be identified by a distinct voltage value that is measured at the identification pin 14.

5 Referring now to FIG. 3, a method of detecting and identifying an accessory connected to an electronic device, according to the present invention, will now be described. 10 The method comprises the first step 310 of generating an interrupt signal from a change in voltage at an identification pin of the electronic device.

, Next, in step 320, an indication of the voltage at the 15 identification pin is obtained. Preferably, this is achieved using an analogue to digital converter.

. .. The final step 330 is to identify the accessory connected using the indication of the voltage at the identification . . 20 pin. This may be achieved by way of a lookup table or the I,. like. Thus, the present invention provides a simple method and apparatus for both detecting and identifying an accessory 25 (from a number of accessories being connected to the electronic device 11, whilst requiring only one dedicated pin, namely the identification pin 14. It will be appreciated that the ground pin 18 is a standard pin that is used for aligning the ground planes of the accessory 30 and the electronic device 11, and not just for providing a second connection to the resistor Racc 52.

The present invention does not suffer from the same problems encountered when using a discrete interrupt pin for the detection of an accessory, or from polling the 5 voltage at the identification pin 14.

Thus, for the present invention, the voltage at the identification pin of the electronic device is used to detect and identify the accessory. In this way, only a 10 single pin is required for both the detection and identification of the accessory. Furthermore, since the change in voltage caused by connection of the accessory generates the interrupt signal used for detecting the . accessory, there is no need for a processor 60 to poll . . 15 for the accessory.

In this manner, the problems identified in the background

of the invention are substantially alleviated.

20 All other features and implementations herein described -..DTD: and/or illustrated in the drawings are considered solely as preferred additions and/or alternatives, and are not limiting on the scope of the present invention.

25 As can be also seen in FIG. 1 and FIG. 2, the voltage across the resistor R2 can also be used to enable and disable, as appropriate, a voltage regulator 30. The -

voltage regulator is connected at VIN to a voltage source VBAT, and at VOUT to a further pin on the connector 12, 30 namely the VEXT pin 32. This pin is preferably used when

13 an accessory requires a voltage supply from the electronic device 11.

When an accessory is connected to the electronic device 5 11, as previously described, the voltage across the resistor R2 is high. This high signal enables the voltage regulator, such that a voltage source is provided at the VEXT pin 32 of the connector 12.

10 When no accessory is detected, the voltage across the resistor R2 is low. This low signal disables the voltage regulator, such that no voltage source is provided at the VEXT pin 32 of the connector 12.

::; . . , 15 In this way, a voltage supply is automatically made available on the VEXT pin 32 to an accessory operably coupled to the electronic device 11 via the connector . :. upon detection of the accessory.

20 Whilst the specific and preferred implementations of the embodiments of the present invention are described above, it is clear that one skilled in the art could readily apply variations and modifications of such inventive concepts.

Claims

Clams 1. An electronic device (11) comprising: an interface connector

(12) having an 5 identification pin (14); an interrupt generation mechanism (10), operably coupled to said identification pin (14), that generates an interrupt signal in response to a status change identified at the identification pin (14) when an 10 accessory (50) is connected to the interface connector (12), and a processor (60), operably coupled to said interrupt generation mechanism (10) to receive an . interrupt notification that an accessory is connected to . e, 15 said interface connector (12) and either: determines from a level of said interrupt signal a type of accessory connected to the interface connector (12); or said processor is operably coupled to said .. 20 identification pin (14) and identifies a type of accessory in response to said status change.

2. The electronic device (200) according to Claim 1, further characterized in that said status change is a 25 voltage change, wherein an amount of said voltage change is indicative of a type of accessory connected to said electronic device (11) via said interface connector (12) .

3. The electronic device (200) according to Claim 1 30 or Claim 2, further characterized by a memory element (70) operably coupled to said processor (60) to provide

- 15 an indication of a type of accessory connected to said electronic device (11) based on said level of said interrupt signal or said status change.

5 4. The electronic device (200) according to Claim 1 or Claim 2 or Claim 3, further characterized in that said electronic device is a mobile communication device, for example a mobile phone.

10 5. A method (300) of detecting and identifying an accessory connected to an electronic device (11), the method comprising the step of: detecting a status change on an identification pin . (14) of an interface connector (12) indicating an . 15 accessory has been connected thereto; the method characterized by the steps of: À,,. generating an interrupt signal, in response to said status change on said identification pin (14); and determining a type of accessory (50) connected to .. À 20 the interface connector (12) from either: a level of said interrupt signal; or a level of said status change.

6. An electronic device substantially as hereinbefore described with reference to, and/or as illustrated by, 25 FIG. or FIG. 2 of the accompanying drawings.

7. A method (300) of detecting and identifying an accessory connected to an electronic device (11) substantially as hereinbefore described with reference 30 to, and/or as illustrated by, FIG. 3 of the accompanying drawings.