Conventionally, as a method of connecting a host computer (hereinafter referred to as the “host”) and a storage device such as an optical disk device or a hard disk device (hereinafter referred to as the “device”), Serial ATA as a high-speed serial transfer protocol standard has been formulated.
With the Serial ATA standard, negotiation referred to as the OOB (Out of Band) sequence is conducted prior to the data transfer. The OOB sequence is performed according to the following routine shown in FIG. 7.
Specifically, after the host is turned on, it sends a COMRESET signal to the device. When the device receives the COMRESET signal, it sends a COMINIT signal to the host. Subsequently, when the host receives the COMINIT signal, it sends a COMWAKE signal to the device, and, when the device receives the COMWAKE signal, it sends a COMWAKE signal to the host.
As described above, the foregoing negotiation is conducted by repeating the operation of the host or the device detecting the respective signals sent by the other. Data transfer is started when the negotiation is performed normally. The COMRESET signal, the COMWAKE signal and the COMINIT signal are collectively referred to as the OOB signal.
The OOB signal is a signal that repeats a period (burst period) of a constant length in which a burst signal defined in the Serial ATA standard is transmitted, and a no-signal period (space period), and the length of the burst period and the space period as well as the frequency thereof are defined in the standard. Specifically, the burst period and the space period of the COMRESET signal and the COMINIT signal are approximately 106.7 [ns] and approximately 320 [ns], respectively, and the number of burst periods is 6 times. Meanwhile, the burst period and the space period of the COMWAKE signal are approximately 106.7 [ns], respectively, and the number of burst periods is 6 times. Generally speaking, a receiving apparatus that is compliant with the Serial ATA standard determines that an OOB signal has been detected upon detecting the burst period and the space period 3 times or more in succession.
Nevertheless, the receiving apparatus sometimes falsely detects noise as an OOB signal. Thus, Japanese Published Unexamined Application No. 2006-203338 (Patent Document 1) discloses a method of preventing such false detection by using a squelch detection circuit that changes the threshold according to the output.