Sideband communication on the standard parallel SCSI bus

摘要

A power supply line of a communications interface provides communication between two devices when one device is unable to utilize the communications interface in a standard manner. The power supply line is specified to operate within a first voltage range and normally operates at a first voltage within a second voltage range, the second voltage range being within the first voltage range. A voltage circuit changes the power supply line to a second voltage outside of the second voltage range but within the first voltage range. A voltage detecting circuit coupled to the power supply line asserts a signal indicating when the second voltage is present on the power supply line, thereby providing communication between the first device and the other device.