NEC MH4500 manual Scsi Controllers

The IDE controller features:

PIO and IDE DMA/bus master operations

Mode 4 timings

transfer rates up to 22 MB/second

Tbuffering for PCI/IDE burst transfers master/slave IDE mode.

SCSI Controllers

The system board contains two SCSI controllers: a narrow SCSI controller (SYM53C810AE) on the PCI-A bus, and a dual-channel wide LVD/SE (Ultra2/Ultra) SCSI controller (SYM53C896) on the PCI-B bus. The narrow controller provides support for legacy 8-bit SCSI devices in the 5 1/4-inch drive bays, including the factory installed SCSI CD-ROM drive. The wide controller drives one SCSI backplane and provides support for external expansion.

Internally, each wide channel is identical, capable of operations using either 8- or 16-bit SCSI providing 10 MB/sec (Fast-10) or 20 MB/sec (Fast-20) throughput, or 20 MB/sec (Ultra), 40 MB/sec (Ultra-wide) or 80 MB/sec (40 MHz) (Ultra-2).

The SYM53C810AE (narrow) contains a high-performance SCSI core capable of Fast 8-bit SCSI transfers in single-ended mode. It provides programmable active negation, PCI zero wait-state bursts of faster than 110 MB/sec at 33 MHz, and SCSI transfer rates from 5 to 10 MB/sec. The narrow SCSI comes in a 100-pin rectangular plastic quad flat pack (PQFP).

The Sym53C896 (wide) contains a high-performance SCSI bus interface. It supports SE mode with 8-bit (10 or 20 MB/sec) or 16-bit (20 or 40 MB/sec) transfers and LVD mode with 8-bit (40 MB/sec) or 16-bit (80 MB/sec) transfers in a 329-pin ball grid array (BGA) package.

Each controller has its own set of PCI configuration registers and SCSI I/O registers. As a PCI 2.1 bus master, the SYM53C896 supports burst data transfers on PCI up to the maximum rate of 132 MB/second using on-chip buffers.

In the hot-swap bay, the system supports up to six, one-inch high SCSI hard disk drives. Also, in the 5 1/4-inch bays, the system supports three SCSI or IDE devices (the SCSI controller itself supports more devices, but the 5 1/4-inch bay can only hold a maximum of three devices).

A wide SCSI cable provides two connectors for Ultra SCSI devices, one of which is used for the SCSI backplane. However, SCSI devices do not need to operate at the ultra transfer rate. All drives on the bus must be Ultra-2 (LVD) to run at 80 MB/sec (40 MHz). The 5, 10, and 20 MHz operations can coexist on the bus and each device interacts at its appropriate speed.

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