Data bus controller having a level setting circuit.

摘要

Disclosed is a small computer system interface device capable of transmitting data between a central digital data processing device (30) and an external device (60) without the need for terminal resistors coupled between the SCSI and the central digital data processing device. A pair of data buses each containing equal number of data lines (33) supply data to a protocol controller (41) which identifies the number of data lines being used to transfer data and then transfers the supplied data to a disk drive unit using the full number of data lines provided by said pair of buses. When the number of bus lines used is less than that provided by both buses, the protocol controller signals a level setting circuit (42) to set the number of bus lines unused by the external device to transfer data from the central digital processing device inactive so as to allow the throughput of data between the digital processing device, SCSI and disk drive unit. <IMAGE>