Emulex MD21/S2, Technical Manual

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MD21 Disk Controller Overview
2.2.2 FUNCTIONAL OVERVIEW
Figure 2-2 is a block diagram that shows the major functional
elements of the MD21. The MD21 is organized around the 8031
microprocessor, the SCSI protocol controller, the disk formatter,
and the buffer controller. The disk formatter and the buffer
controller are custom VLSI chips designed by Emulex.
Two buses are used in the MD21: the data bus and the microprocessor
bus.
The data bus is connected directly to the disk formatter, SCSI
protocol controller, buffer memory, and buffer controller. The
buffer controller is connected directly to the data bus and the
microprocessor bus, providing an interface between them.
Therefore, the buffer controller provides a data path between the
buffer memory, the 8031 microprocessor, disk formatter, and SCSI
protocol controller.
The microprocessor bus provides a path for transmission of control
and status information between the 8031 microprocessor, EPROM,
buffer controller, and disk interface. This bus is completely
separate from the data bus. The microprocessor may access the data
bus via the buffer controller interface.
The MD21 SCSI Interface is implemented using a single LSI chip on
the MD21 Controller. In response to commands from the initiator,
the chip establishes and monitors SCSI bus phases appropriate to
the command. It performs SCSI signal control and timing functions.
General Description 2-3