Abstract

A polling controller (21) for a polling system in which a central station (11) sequentially contacts a series of remote stations (13) in order to transmit data to or receive data from the remote stations is disclosed. The polling controller (21) is connected between the telco terminals of a central station modem (23) and a telco line (18). When the central station modem (23) goes off-hook, a DTMF transceiver and answer tone detector (45) is connected to the telco line (18). When a dial code that follows the telephone number of the remote station being called by the central station modem is detected, the central station modem is placed on hold. Thereafter, a transfer code, which may be the same as the dial code, is sent to the called remote station (13). In response, a switch (31) at the remote station (13) connects its telco line (18) to a port, determined by the nature of the dial code, and transmits an answer tone to the polling controller (31). When the answer tone is detected by the polling controller (31), the central station modem is taken off hold and allowed to communicate with the selected modem (35a, 35b, ...) of the remote station (13). If a priority telephone (33) connected to one of the ports of the switch (31) of the remote station (13) goes off-hook, the switch (31) of the remote station (13) disconnects the remote station modem and generates a priority interrupt tone that causes the central station modem (23) to be disconnected. As a result, telco contact between the central station and the remote station is broken and the telephone (33) is given immediate access to the telco system.