GB2276287A

GB2276287A - Electronic device with mode switching produced by applying switching signal to device output

Info

Publication number: GB2276287A
Application number: GB9305825A
Authority: GB
Inventors: Kenneth Jahn Lavrsen
Original assignee: Motorola AS
Current assignee: Motorola Solutions Danmark AS
Priority date: 1993-03-20
Filing date: 1993-03-20
Publication date: 1994-09-21
Anticipated expiration: 2013-03-20
Also published as: GB9305825D0; DE4409379A1; DE4409379C2; GB2276287B

Description

ET.ECTRONIC DEVICE WITM MODE SWITCHING

Field of the Invention

This invention relates to electronic devices which operate in at least two modes and have an output for outputting a signal, for example an audio signal, and an input for receiving a mode change signal.

Background to the Invention

In an electronic device for example a two-way secure radio, with an audio output, for example a loudspeaker, it is often a problem providing enough pins on accessory connectors for the various inputs and outputs. For example, a microphone connector may be provided with eight pins which will be needed for power supply, ground connection, on/off and various modes. In a complex radio, the eight pins can readily be used up for controlling the various modes. Simply providing more pins is not a satisfactory solution as this may involve non-standard connectors as well as requiring additional wires in the connecting cable (if any).

There is a need to increase the functionality of a connector or of the inputs and outputs of an electronic device without increasing the number of input and output pins.

Summary of the Invention

According to the present invention, an electronic device is provided which is arranged to operate in at least two modes and has an output for outputting a signal generated by the device in a first mode and has an input for receiving a mode change signal for changing the mode of operation of the device between first and second modes. The invention is characterized in that the output and the mode change input are coupled within the device to a common external connector, sensor circuitry is provided for sensing a signal on the common connector and for causing a change of mode of the 2 device in response to such a signal, and means are provided for preventing the signal generated by the device, which is output on the connector, from causing the sensor circuitry to activate and change the mode of the device. 5 In this manner, the common connector acts in one mode as an output, for example an audio output and simultaneously reacts to receipt of a change of mode signal causing the circuitry to change modes. In a first embodiment of the invention the output signal is prevented from causing a change of mode by providing voltage threshold detector means in the sensor for sensing the crossing of a sensor threshold on the connector and voltage range limiting means in the output of the device for preventing the output signal from crossing said threshold in the first mode.

In an alternative embodiment of the invention, integrator means are provided in the sensor means and the sensor means are arranged to respond to a change of voltage on the connector below a pre-determined frequency, while frequency limiting means are provided for limiting the output to frequencies above said predetermined frequency. Preferred embodiments of the invention will now be described by way of example only, with reference to the drawings. 25 Brief Description of the Drawinas Figs 1 to 9 are circuit diagrams of nine different embodiments of the invention, and 30 Fig. 10 is a table showing different modes of a radio in accordance with the invention. Detailed Description of the Preferred Embodiment

Referring to Fig. 1, a radio is shown within a dotted line 10. The radio has operative circuitry 11 which is capable of functioning in a number of modes, including normal mode and key load mode. In normal mode, the operative circuitry 11 is operative as a radio, for receiving and 3 transmitting radio signals and receiving audio signals from a microphone and outputting signals at a loudspeaker. In this mode, further inputs to the operative circuitry 11 (not shown) have functions corresponding to that mode, for example a push-to-talk switch, a monitor input and other inputs and outputs. The operative circuitry 11 includes a secure encryption and decryption module 12 which encrypts signals for transmission and decrypts received signals using an encryption key. The operative circuitry 11 can switch to a key load mode in which a new key can be loaded into the encryption circuitry 12 on an input 13. The input 13 is connected to the encryption module 12 and to the rest of the operative circuitry 11 by a two-way switch 14. The operative circuitry 11 has a mode change input 15 for receiving a signal to change modes.

The operative circuitry 11 has an audio output 20, which is connected to a power amplifier of medium output impedance e.g 10 ohms to 1 kohms. The output of the power amplifier 21 is connected to a pin 22 of an accessory connector. Also connected to pin 22 is an integrator circuit 23, which in turn is connected to a comparator 24. Integrator circuit 23 is connected to the negative input of the comparator 24. A reference voltage (Vref) is connected to the positive input of the comparator 24. The output of the comparator 24 is connected to the mode change input 15 of the operative circuitry 11. On the right side of Fig 1 are shown four alternative accessories for connection to connector pin 22.

The first of these is a simple loudspeaker 30 connected via a blocking capacitor 31. Also shown are a direct short connection to ground 32, a switch to ground 33 and a DC voltage source 34.

The operation of the circuitry is as follows:

In normal mode, the loudspeaker 30 and its capacitor 31 are connected to the pin 22 of the accessory connector. The operative circuitry 11 operates in its normal mode, outputting audio on output 20, which is amplified in amplifier 21 and emitted as sound through the loudspeaker 30.

To switch to key load mode, short-to-ground connector 32 is connected to pin 22 in place of loudspeaker 30. Comparator 4 circuit 34 detects the short to ground (the level on the negative input having fallen below a threshold set by Vref) and the output of the comparator 24 causes operative circuitry 11 to change modes into a key load mode. Among the changes to operative circuitry 11 switch 14 switches the input 13 so as to be connected to the encryption module 12 ready for receipt of an encryption key.

Integrator circuitry 23 prevents the audio output from amplifier 21 from triggering the comparator 24. For example, integrator circuitry 23 has a 1 second time constant, such that only a DC voltage lasting at least one second causes a change on the output of integrated circuitry 23. Likewise, removal of such a DC signal causes comparator 24 to remove the signal provided at its output and causes operative circuitry 11 to change back to normal mode. In changing back to normal mode a number of changes occur, including switching of switch 14 to its other position, so that input 13 serves a different function, eg. monitor input. (The monitor function causes the circuitry 11 to output on the audio output any signal received on the RF channel to which the radio is tuned, thereby allowing the user to examine whether the channel is in use).

Circuit elements 33 and 34 serve the same purpose of shortto-ground 32.

As an alternative to having a long time constant in integrated circuit 23, the voltage range of output amplifier 21 can be limited so that the output never falls below the threshold defined by Vref. Or alternatively, of course, Vref can be supplied to the negative input of comparator 24 and the output voltage of amplifier 21 can be limited so that it never exceeds Vref.

Referring to Fig. 2, radio circuitry 11, power amplifier 21 and connector pin 22 are shown in the same configuration as is shown in Fig. 1. Instead of an integrator and a comparator, Fig. 2 provides a microprocessor 40 having an analog-to-digital input 41. Microprocessor 40 performs a software integration function and when the input on A/D input 41 exceeds a threshold for a predetermined period of time (eg. 1 second), the microprocessor 40 provides a mode change input to the operative circuitry 11.

Referring to Fig. 3, a third example of an embodiment of the invention is shown having an unbalanced output with DC on the output of the amplifier. The circuit comprises a power amplifier 21, an analog detector 50 having its negative input coupled to the output of amplifier 21 via a resistor 51 and also coupled to ground via capacitor 52 and having its positive input connected to the mid-point of a potential divider formed by resistors 53 and 54. As for the circuit of Fig. 1 the output of analog detector 50 causes a change of mode in the operative circuitry of the electrical device.

The detector circuitry 50 provides the change of mode input when the connector pin 22 is connected to ground.

is Fig. 4 shows a further embodiment of the invention having an audio power amplifier with an unbalanced output and no DC on its output, that is to say an amplifier which must not be short circuited to ground. In this case, there is a capacitor 60 coupled between the output of amplifier 21 and the output pin 22. A resistor 61 provides positive bias to the pin 22 and a voltage sensor circuit 62 senses a short circuiting to ground of the voltage on pin 22. The voltage sensor circuit 62 provides the mode change signal to the operative circuitry of the device.

Fig. 5 shows a modification of the circuit of Fig. 4 in which the amplifier 21 has a low output impedance (approximately 0 ohms but less than 10 ohms) for high power output. As well as capacitor 60, there is a high value resistance 65 for power limiting coupled between the capacitor 60 and the output pin 22. The loudspeaker 30 is a low power loudspeaker and there is provislon for connecting an optional high power loudspeaker 66 internal to the electronic device.

Referring to Fig. 6, the audio power amplifier 70 in this circuit has a balanced output and a medium output impedance and DC on its output. A first voltage sensor circuit 71 is coupled to one of the outputs of amplifier 70.

Optional second voltage sensor circuitry 72 can be provided coupled to the second output of amplifier 70. The outputs of 6 amplifier 70 are coupled to separate pins 73 and 74 on an accessory connector, which can be coupled to a loudspeaker 75. Alternatively, one or two switches 76 and 77 can be connected to pins 74 and 73 respectively for short circuiting those pins to ground. Switch 77 need only be provided if optional voltage sensor 72 is also provided. Switching of switch 76 causes voltage sensor 71 to detect the drop in voltage on pin 74 and provide a mode change signal to the operative circuitry of the device.

Referring to Fig. 7, a balanced output amplifier 70 is shown having a lower output impedance. An optional high power loudspeaker 80 can be provided in the channel to the device between the outputs of amplifier 70. A power limiting resistor 80 is provided between one of the outputs of the amplifier 70 and output pin 73. A pull-up resistor 81 is also connected to this output to maintain a positive bias on that output. A low pass filter/integrator 82 is connected to this pin and has associated with it a voltage sensor 83 for sensing a mode change signal on pin 73. In normal use, amplifier 75 is coupled between pins 73 and 74, but upon connection of a short-to-ground 86 to pin 73, voltage sensor 83 detects the drop in voltage on pin 73 and provides a mode change signal to the operative circuitry of the device.

Referring to Fig. 8, a balanced output amplifier 70 is shown with no DC on its output, that is to say an amplifier that must not be short circuited to ground. The circuitry is similar to that of Fig. 6, but has additional blocking capacitors 90 and 91 and pull-up resistors 92 and 93, all of which function similar to the corresponding elements of Fig.

4.

Referring to Fig. 9, an audio power amplifier is shown having low impedance output (high power) that must not be connected to ground. The circuitry is similar to that of Fig. 7 but has a high pass filter network comprising capacitors 100 and 101 coupled between an output of the amplifier and pin 73 and comprising resistor 102 coupled between the mid point of those capacitors and ground. The effect of the high pass filter is to limit the lower frequency range of amplifier 70. Connected to the input of 7 voltage sensor 83 is a low pass filter comprising capacitor 103 and resistor 104, as well as resistor 105 coupling voltage sensor 83 to pin 73. The effect of capacitor 103 is to pass the higher frequencies from the amplifier 70 to ground, thereby causing the voltage sensor 83 to be triggered only by frequencies in the range that have been filtered out by filter network 100 to 102. In operation of this circuit, the output of the amplifier 70 is, in normal mode, output through speaker 75 and this signal does not reach voltage sensor 83, because the frequencies of the signal are filtered away from voltage sensor 83 by RC network 103, 104 and 105. Upon connection of a short-to-ground connection 86 to pin 73, the change in DC level on pin 73 is detected by voltage sensor 83 and a mode change signal is provided to the operative circuitry (not shown in Fig. 9).

The microphone connector can be used for simple microphones, control microphones, keypad microphones, filter programmers and secure key loaders. The microphone connector can operate in three modes, normal, SB9600 and secure (keyload). The radio can reside in 4 states, depending on the current on pin 1 and the voltage on pin 2, as set out in the table in Fig. 10. The microphone connector preferably has 8 pins, which have the functions set out in the following list.

Pin 1 Optional SWB+: Power supply for microphones.

Current from output sets MIC multiplexer in SB9600 mode.

Pin 2 Speaker-/Keyload. Short to ground for 1 sec sets microphone multiplexer in Keyload mode. It has 51 ohms series resistor from the loudspeaker Pin 3 Normal mode: Monitor input (active low) SB9600 mode: BUSY Keyload mode: KID (Secure keyload signal) Pin 4 Ground 35 Pin 5 Microphone - ON/OFF Pin 6 Normal mode: PTT (Push-to-talk) input SB9600 mode: BUSKeyload mode: WE (secure keyload signal) Pin 7 Normal mode: auxilliary input (analog 4 steps) 8 SDB9600 mode: BUS+ Keyload mode: Key/Fail (Secure keyload signal) Pin 8 Speaker+/Handset Audio (Handset Audio default) The invention allows for changing between different modes of the secure radio. Secure mode is detected by the software by monitoring DC on the speaker line. This voltage drops to 0 when the speaker line is connected to ground. The software changes to keyload mode when the voltage has been below 250 millivolts for 200 milliseconds.

It will be understood that the invention is not limited to the above examples but other modifications can be made within the scope of the invention. For example, the output from the electronic device could be a radio frequency output instead of an audio frequency output. The electronic device could be an integrated circuit with a limited number of pins.

The invention allows an output connector which in one mode of operation of the circuit provides an output signal and in the other mode is not required for outputting a signal to be used as a mode - change input for changing between the first mode and the second mode. In the second mode, in which the output signal is generally (but not necessarily) not required, the dual purpose connector is acting as an input.

9

Claims

1. An electronic device arranged to operate in at least first and second modes and arranged to generate a signal in the first mode, comprising an output for outputting the signal generated by the device in the first mode and an input for receiving a mode change signal for changing the mode of operation of the device between the first and second modes, characterized in that the output and the mode change input are coupled within the device to a common external connector, sensor circuitry is provided for sensing a signal on the common connector and for causing a change of mode of the device in response to such a signal, and means are provided for preventing the signal generated by the device from causing the sensor circuitry to activate and change the mode of the device.

2. An electronic device according to claim 1 wherein the device is arranged to generate an audio signal in the first mode and to output the signal via the common external connector.

3. An electronic device according to claim 1 or 2 further comprising voltage threshold detector means in the sensor for sensing the crossing of a sensor threshold on the connector and voltage range limiting means in the output of the device for preventing the output signal from crossing said threshold in the first mode.

4. An electronic device according to claim 1 or 2 further comprising integrator means in the sensor means, wherein the sensor means are arranged to respond to a change of voltage on the connector below a predetermined frequency, while frequency limiting means are provided for limiting the output to frequencies above said pre-determined frequency.

5. A radio comprising encryption circuitry and means for accepting an encryption key, the radio being operable in a first mode for generating an audio signal and a second mode for receiving the encryption key, the radio further comprising an output for outputting the signal generated by the radio in the first mode and an input for receiving a mode change signal for changing the mode of operation of the radio between the first and second modes, characterized in that the output and the mode change input are coupled within the radio to a common external connector, sensor circuitry is provided for sensing a signal on the common connector and for causing a change of mode of the radio in response to such a signal, and means are provided for preventing the signal generated by the radio from causing the sensor circuitry to activate and change the mode of the radio.