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A method of transmission-reception over a serial bus placed, when idle, in a first state at a first voltage, including: a transmit circuit capable of coding a transmission according to a first protocol in which the respective states of the bits are conditioned by time periods of fixed levels, indiff

A method of transmission-reception over a serial bus placed, when idle, in a first state at a first voltage, including: a transmit circuit capable of coding a transmission according to a first protocol in which the respective states of the bits are conditioned by time periods of fixed levels, indifferently in the first state or in a second state at a second voltage smaller than the first one; a receive circuit capable of interpreting a communication according to the first protocol; and a protocol converter, interposed between the bus and the transmit and receive circuits, to convert the signals to be transmitted to a second protocol in which the respective states of the bits are conditioned by respective time periods of fixed levels in the first state, and to convert the received signals from the second protocol to the first protocol.

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1. A device of transmission-reception over a single-wire serial bus placed, when idle, in a first state at a first voltage, comprising: a transmit circuit configured to code a transmission according to a first protocol in which the respective states of bits are conditioned by time periods of fixed l

1. A device of transmission-reception over a single-wire serial bus placed, when idle, in a first state at a first voltage, comprising: a transmit circuit configured to code a transmission according to a first protocol in which the respective states of bits are conditioned by time periods of fixed levels, in the first state or in a second state at a second voltage smaller than the first voltage;a receive circuit configured to interpret a communication according to the first protocol; anda protocol converter, connected to the bus and the transmit and receive circuits, configured to convert signals to be transmitted to a second protocol in which respective bit states are conditioned by respective time periods of fixed levels in the first state, and to convert received signals from the second protocol to the first protocol, wherein the protocol converter converts the signals to be transmitted from the first protocol to the second protocol in response to an activated state of a control signal, which indicates that a slave device is powered over the single-wire serial bus, and does not convert the signals to be transmitted to the second protocol in response to a deactivated state of the control signal. 2. The device of claim 1, wherein said protocol converter is activated when another device with which it communicates over the bus extracts its power supply from the bus. 3. A method for controlling the device of claim 2, comprising: activating the protocol converter;initiating a communication towards said other device; andin the absence of a response:deactivating the protocol converter and;initiating the communication again. 4. The device of claim 1, wherein periods of pulses of the first protocol are respectively equal to periods of pulses of the second protocol plus an interval in the second state according to the second protocol. 5. A method for controlling the device of claim 1, comprising: detecting an absence of a power supply voltage originating from a source other than the bus; andactivating said protocol converter. 6. A system of communication between a first device and at least one second device over the single-wire serial bus, wherein at least one of the devices is in accordance with claim 1. 7. A device of transmission-reception over a single-wire serial bus placed, when idle, in a first state at a first voltage, comprising: a transmit circuit configured to code a transmission according to a first protocol in which the respective states of bits are conditioned by time periods of fixed levels, in the first state or in a second state at a second voltage smaller than the first voltage;a receive circuit configured to interpret a communication according to the first protocol; anda protocol converter, connected to the bus and the transmit and receive circuits, configured to convert signals to be transmitted to a second protocol in which respective bit states are conditioned by respective time periods of fixed levels in the first state, and to convert received signals from the second protocol to the first protocol, wherein the protocol converter comprises:a first stage of conversion from the first protocol to the second protocol having an input connected to an output of the transmit circuit;a second stage of conversion from the second protocol to the first protocol having an input connected to the single-wire serial bus;a first two-to-one multiplexer having inputs respectively connected to the output of the transmit circuit and to an output of the first conversion stage, and having an output controlling a switch conditioning the state of the single-wire serial bus; anda second two-to-one multiplexer having respective inputs connected to the single-wire serial bus and to an output of the second conversion stage, and having an output connected to an input of the receive circuit. 8. A device for communication on a single-wire bus, comprising: a transmit circuit configured to transmit signals according to a first protocol in which states of bits are indicated by different time periods at a first voltage level or a second voltage level lower than the first voltage level; anda protocol converter configured to convert the transmitted signals from the first protocol to a second protocol in response to an active state of a control signal, which indicates that a slave device receives power over the single-wire bus, and to not convert the transmitted signals from the first protocol to the second protocol in response to a deactivated state of the control signal, wherein states of bits in the second protocol are indicated by different time periods at the first voltage level and wherein the protocol converter is connected between the transmit circuit and the single-wire bus. 9. The device of claim 8, wherein the protocol converter comprises: a first conversion stage, configured to convert from the first protocol to the second protocol, having an input connected to an output of the transmit circuit;a second conversion stage, configured to convert from the second protocol to the first protocol, having an input connected to the single-wire bus;a first two-to-one multiplexer having inputs respectively connected to the output of the transmit circuit and to an output of the first conversion stage, and having an output coupled to a switch that controls the state of the single-wire bus; anda second two-to-one multiplexer having inputs respectively connected to the single-wire bus and to an output of the second conversion stage, and having an output connected to an input of a receive circuit. 10. The device of claim 8, wherein periods of pulses of the first protocol are respectively equal to periods of pulses of the second protocol plus an interval at the second voltage level according to the second protocol. 11. The device of claim 8, wherein bits of the second protocol are separated by pulses at the second voltage level and wherein the pulses at the second voltage level have durations less than one-quarter of a shortest time period at the first voltage level. 12. A method for communication on a single-wire bus, comprising: transmitting signals on the single-wire bus according to a first protocol in response to a deactivated state of a control signal, wherein states of bits according to the first protocol are indicated by different time periods at a first voltage level or a second voltage level lower than the first voltage level; andtransmitting signals on the single-wire bus according to a second protocol in response to an activated state of the control signal, wherein the states of bits according to the second protocol are indicated by different time periods at the first level and wherein the activated state of the control signal indicates that a slave device receives power over the single-wire bus. 13. The method of claim 12, wherein periods of pulses of the first protocol are respectively equal to the periods of pulses of the second protocol plus an interval at the second voltage level according to the second protocol. 14. The method of claim 12, further comprising transmitting signals to a second device on the single-wire bus according to the second protocol and, in the absence of a response from the second device, transmitting signals to the second device on the single-wire bus according to the first protocol. 15. The method of claim 12, wherein bits of the second protocol are separated by pulses at the second voltage level and wherein the pulses at the second voltage level have durations less than one-quarter of a shortest time period at the first voltage level.