The invention relates to a method of programming a processing unit by firmware in a protocol converter for providing first data received from a telephone device in accordance with a first protocol to a headset system in accordance with a second protocol and for providing second data received from the headset system in accordance with the second protocol to the telephone in accordance with the first protocol, the operation of the protocol converter being controlled by the processing unit. The invention further relates to a protocol converter, such as an Electronic Hook Switch adapter, for providing first data received from a telephone device in accordance with a first protocol to a headset system in accordance with a second protocol and for providing second data received from the headset system in accordance with the second protocol to the telephone device in accordance with the first protocol. The headset system provides firmware to the protocol converter in accordance with the second protocol.