Not all microcontrollers output the same logic state after power-up or reset. 8051-type microcontrollers, for example, output logic-high levels on the ports, whereas other models power up with logic low levels after reset. In Figure 6-2, configuration (a) the shutdown signal is applied on the cathode side of the photodiode within the optocoupler. A high logic level causes the OPA561 to be enabled, and a low logic level shuts down the OPA561. In Figure 6-2, configuration (b), with the logic signal applied on the anode side, a high level causes the OPA561 to shut down, and a low level enables the op amp.