Audio Accessory Circuitry and Method Compatible With Both MSFT Mode and Digital Communication Mode

摘要

An audio accessory key detection system (40) includes a host circuit (2-3) coupled to communicate via a microphone line (7) with an accessory circuit (3-3) in either a MSFT mode or a digital communication mode. Depletion mode transistors (44-1,2,3) in the accessory circuit are coupled between keys (15-1,2,3) of the accessory circuit, respectively. The depletion mode transistors are allowed to remain conductive for MSFT mode operation. For digital communications mode operation, the host circuit sends a command via the microphone line to a key detector and controller circuit (29A) in the accessory circuit. In response, a voltage is generated to turn the depletion mode transistors off so as to allow digital communications mode operation between the accessory circuit and the host circuit.

主权项

1. An audio accessory key detection system comprising:
(a) a host circuit including a host controller, and a bias circuit coupled by a first resistor to a microphone line; (b) a host transceiver in the host circuit coupled to the microphone line and the host controller; (c) an analog to digital converter in the host circuit for digitizing an analog signal level on the microphone line and conveying a digital representation of the analog signal level to the host controller during a MSFT mode of operation; (d) an accessory circuit including a microphone and a microphone bias circuit each coupled to the microphone line, a plurality of keys that may be actuated by a user to control a corresponding function to be performed by the host circuit, a key detector and controller circuit coupled to the keys, and an energy storage circuit coupled to the microphone line coupled to deliver a supply voltage to the key detection and controller circuit; (e) an accessory transceiver in the accessory circuit coupled to the microphone line and to the key detection and controller circuit; and (f) a plurality of depletion mode transistors each having a source coupled to the microphone line, a drain coupled to a terminal of a corresponding key, and a gate controlled so as to allow the depletion mode transistors to remain in a conductive condition during the MSFT mode of operation and to cause the depletion mode transistors to be in a non-conductive condition during a digital communication mode of operation.