Communication device and image forming apparatus

A receiving communication device configured to receive a signal from a transmitting communication device, the receiving communication device comprising:

• a signal reception circuit configured to receive a differential signal transmitted from the transmitting communication device via a communication cable, and convert the differential signal into binary data;
• a squelch detection circuit configured to compare an amplitude level of the differential signal with threshold voltages to detect a non-squelch state and a squelch state;
• a start pattern detection circuit configured to detect a state in which a predetermined start pattern is detectable from the binary data based on the differential signal, as a receivable state;
• a register that stores a squelch setting value associated with the threshold voltages to detect the non-squelch state and the squelch state;
• a DC voltage selection circuit configured to select two DC voltages from among multiple DC voltages in accordance with the squelch setting value output from the register, and supply, to the squelch detection circuit, the two DC voltages as the threshold voltages to detect the non-squelch state and the squelch state;
• a squelch setting control circuit configured to, in response to the start pattern detection circuit detecting the receivable state, change the squelch setting value to increase or decrease the squelch setting value in steps and sequentially set the squelch setting value in the register as a reception squelch setting value used for the receivable state;
• and
• a table configured to store the squelch setting value, wherein
• the squelch setting control circuit is further configured to
• sequentially store the squelch setting value in the table,
• store, in response to the start pattern detection circuit detecting the receivable state, a success flag in the table in association with a squelch setting value used at time of the detecting of the receivable state,
• read success flags associated with different squelch setting values from the table, count a number of success flags, and obtain a number of success steps, and
• set a center value of squelch setting values of the success steps or a value closer to a maximum squelch setting value by one step among middle squelch setting values of the success steps, as the reception squelch setting value.