Patent ID: 8184985

Claim:
A control circuit for an optical transmitter/receiver that transmits/receives an optical signal, comprising: a memory having a digital value storage area and an area that stores predetermined limit values; a register; an analog/digital conversion circuit that receives a plurality of analog signals indicating operating parameters related to an operating characteristic or environment of the optical transmitter/receiver, from the optical transmitter/receiver, converts the analog signals to respective digital values, and stores the digital values in the digital value storage area of the memory; a comparison logical circuit that compares the plurality of digital values with corresponding limit values stored in the memory, generates flag values corresponding to comparison results, and stores the flag values in the register, wherein each flag value consists of (i) a first flag indicating whether the digital value corresponding to the flag value is outside upper and lower limits of a first range, (ii) a second flag indicating whether the digital value corresponding to the flag value is outside upper and lower limits of a second range and the first range, the second range encompassing and being wider than the first range, and (iii) a third flag indicating whether the digital value corresponding to the flag value is higher than the upper limit of the first range and/or the second range indicated by the first and/or second flags or lower than the lower limit of the first range and/or the second range indicated by the first and/or second flags; and an outside interface that allows an outside host apparatus to access the memory and the register according to a command and an address received from the host apparatus, wherein the host apparatus reads the flag values to monitor an operating condition of the optical transmitter/receiver from outside.