Avago Technologies LSI53C876E - Manual (Page 35)

SCSI Functional Description 2-13
2.2 SCSI Functional Description
2.2.1 Two SCSI Controllers
The LSI53C876 provides two SCSI controllers on a single chip. Each
SCSI controller provides a SCSI function that supports an 8-bit or 16-bit
bus. Each supports Ultra SCSI synchronous transfer rates up to
40 Mbytes/s, Ultra SCSI synchronous transfer rates up to 20 Mbytes/s,
and asynchronous transfer rates up to 14 Mbytes/s on a wide SCSI bus.
The SCSI functions are programmed with SCSI SCRIPTS, making it
easy to “fine tune” the system for specific mass storage devices or
SCSI-2 requirements.
The LSI53C876 offers low-level register access or a high-level control
interface. Like first generation SCSI devices, the LSI53C876 is accessed
as a register-oriented device. Error recovery and diagnostic procedures
use the ability to sample and/or assert any signal on the SCSI bus. In
support of SCSI loopback diagnostics, each SCSI core may perform a
self-selection and operate as both an initiator and a target.
The LSI53C876 is controlled by the integrated SCRIPTS processor
through a high-level logical interface. Commands controlling the SCSI
core are fetched out of the main host memory or local memory. These
commands instruct the SCSI core to Select, Reselect, Disconnect, Wait
for a Disconnect, Transfer Information, Change Bus Phases and, in
general, implement all aspects of the SCSI protocol. The SCRIPTS
processor is a special high-speed processor optimized for SCSI protocol.
2.2.2 SCRIPTS Processor
The SCSI SCRIPTS processor allows both DMA and SCSI commands
to be fetched from host memory or internal SCRIPTS RAM. Algorithms
written in SCSI SCRIPTS control the actions of the SCSI and DMA
cores. The SCRIPTS processor executes complex SCSI bus sequences
independently of the host CPU.
Algorithms may be designed to tune SCSI bus performance, to adjust to
new bus device types (such as scanners, communication gateways, etc.),
or to incorporate changes in the SCSI-2 or SCSI-3 logical bus definitions