The L9218 requires a 5 V power supply and single battery to operate. This is a forward battery only device. Additionally, a low-power scan mode, wherein all circuitry except the off-hook supervision is shut down to conserve power, is available. Via the logic inputs, a low or high current limit may be selected. The low value is set via a single external resistor, and the high value is 1.4 times the low value. Device overhead is fixed and is adequate for 3.14 dBm into 900 of on-hook transmission. Both the loop supervision and ring trip supervision functions are offered with user-controlled thresholds via external resistors.