DP5380 datasheet(2/32 Pages) NSC

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10 Functional Description

11 OVERVIEW

The ASI is designed to be used as a peripheral device in a

P-based application and appears as a number of read

write registers Write registers are programmed to select de-

sired functions Status registers provide indication of operat-

ing conditions

For best performance a DMA controller can be easily inter-

faced directly to the ASI The ASI provides requestac-

knowledge and wait-state signals for the DMA interface

The SCSI bus is easily controlled via the ASI registers Any

bus signal may be asserted or deasserted via a bit in the

appropriate register and the state of every signal is avail-

able by reading registers This direct control over SCSI sig-

nals allows the user to implement all or part of the protocol

in firmware The ASI provides hardware support for much of

the protocol

The ASI provides the following SCSI support

Programmed-IO transfers for all eight information trans-

fer types with or without parity

Data transfers via DMA in either block or non-block

mode The DMA interface supports most devices

Individual settingresetting and monitoring of every SCSI

bus signal

Automatic release of the bus for BSY loss from a TAR-

GET SCSI RST and lost arbitration

Automatic bus arbitrationthe mP has only to check for

highest priority

Selection or Reselection of any bus device The ASI will

respond to both Selection and Reselection

Optional automatic monitoring of the BSY signal from a

TARGET with an interrupt after releasing control of the

bus

Figure 1 shows an ASI in a typical application a low cost

embedded SCSI disk controller In this application the 8051

single-chip mP acts as the controller and the dual DMA

channels in the DP8475 allow one for the disk data and the

other for SCSI data The PAL

provides chip selection as

well as determining who has control of the bus The advan-

tage of using a mP with on-board ROM is that there is more

free time on the external bus

TLF9756 – 2

FIGURE 1 ASI Application

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