Abstract: A data access arrangement circuit (60) for supplying electrical isolation between a telephone line (11) and a data device, such as a data terminal or a computer, connected to a modem (10). An isolation circuit (17) connected between a first modem circuit (15) having a transmitter (19), a receiver (20), and a controller (18), and a second modem circuit (16) connected to the telephone line (11), couples signals between the first modem circuit (15) and the second modem circuit (16), thereby electrically isolating the first modem circuit (15) from the second modem circuit (16). The second modem circuit (16) conditions an incoming analog telephone signal received via the telephone line (11) to supply an incoming digital data signal to the receiver (20). The second modem circuit (16) further conditions an outgoing digital data signal received from the transmitter (19) to supply an outgoing analog telephone signal for transmission over the telephone line (11).