Abstract: A single chip SCSI controller circuit has a pair of input and output first in, first out (FIFO) buffers as well as a main buffer. The circuit supports synchronous and asynchronous data transfers which are fully compatible with the SCSI-II specification. A mode select pin may be selectively actuated by the user or by attached interface circuitry to configure the chip for either microchannel architecture (MCA) or industry standard architecture (ISA) compatibility.