Incorporated Protective Circuit With Microcoded Switch Hook and Level Adjustment Functions
Original Publication Date: 1985-Jan-01
Included in the Prior Art Database: 2005-Feb-18
The attachment of a modem to the U.S. Public Switched Network is accomplished by the use of an FCC Registered Incorporated Protective Coupler (IPC) and a data jack which is provided by the telephone companies. Today modems comprise microprocessors and VLSI circuits, while IPCs are generally made of analog components. This causes the IPC to have almost the same size as that of the modem circuitry and to represent a substantive portion of the cost of the whole modem. This article describes a technique which permits two of the functions performed by the IPC switch hook detection and transmit level adjustment) to be implemented by microcode, thereby reducing the size and cost of the IPC and improving its performance. The IPC is connected to the data jack by three pairs of wires. The first pair is the telephone pair (DT, DR).