Abstract: A hold circuit arrangement for a telephone, wherein the telephone is coupled to an extension release circuit of an external telephone, the hold circuit comprising an input control terminal; a tri-state input device used for generating a signal for the input control terminal; a power supply used for providing a high impedance level for the input control terminal; a hold button circuit used for allowing a hold button of the telephone to convert a status of the hold circuit through the tri-state input device after the hold function is activated regardless of whether the telephone is off-hook or on-hook; and a detecting circuit used for alternately providing a high impedance high level signal or a high impedance low level signal to detect the status of the tri-state input device when the hold function of the telephone is activated, and deciding whether the telephone is hold or not, and signaling the power supply to stop providing the high impedance level signal to the input control terminal when the hold function

Abstract: A keyboard scanning circuit for detecting additional user selected functions on a keyboard while the keyboard is being "debounced". The scanning circuit permits the scanning for additional functions without the need for additional scanning ports by detecting whether a row port of the scanning circuit is connected to a source voltage via a resistor, a ground via a resistor, or is floating. The user or the manufacturer using the circuit can set the switches which establish the status of these additional functions.

Abstract: Disclosed is a scanning circuit for an electrical matrix keyboard. The keyboard has extended keys on a voltage line and a ground line. Two extended line detector are incorporated into the circuit for detecting the extended keys without increasing input and output ports of the circuit, so that the circuit can be integrated into a chip at a lower cost.