TEXAS INSTRUMENTS SA555D

The SA555D is a Precision Timer capable of producing accurate time delay or oscillation. In the mono-stable mode of operation the timed interval is controlled by a single external resistor and capacitor network. In the a-stable mode of operation the frequency and duty cycle can be controlled independently with two external resistors and a single external capacitor. The threshold and trigger levels normally are 2/3rd and 1/3rd respectively of VCC. When the trigger input falls below the trigger level the flip-flop is set and the output goes high. If the trigger input is above the trigger level and the threshold input is above the threshold level, the flip-flop is reset and the output is low. When RESET goes low the flip-flop is reset and the output goes low. When the output is low a low-impedance path is provided between discharge and ground.