SN75970B2DGG datasheet(2/23 Pages) TI

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SN75970B

SCSI DIFFERENTIAL CONVERTER-CONTROL

SLLS323A – NOVEMBER 1999 – REVISED JANUARY 2000

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

description (continued)

The differential SCSI bus interface consists of

bipolar bidirectional inputs and outputs that meet

or exceed the requirements of EIA-485 and ISO

8482-1982/TIA TR30.2 referenced by the Ameri-

can National Standard of Information Systems

(ANSI) X3.131-1994 Small Computer System

Interface-2 (SCSI-2) and SCSI-3 Fast-20 Parallel

Interface (Fast-20) X3.277:1996.

The SN75970B is characterized for operation

over the temperature range of 0

°C to 70°C.

The SN75970B consists of nine RS-485 differen-

tial transceivers, nine TTL- or CMOS-level

compatible transceivers, a state machine and

control logic block, a 20-MHz crystal-controlled

oscillator, a timer, a power-up/-down glitch

protection

circuit,

and

thermal-shutdown

protection circuit.

The single-ended or controller interface is

designated as the A side and the differential port

is the B side. Since the device uses the SCSI

control signals to decode the state of the bus and

data flow direction, the terminal assignments must

be matched to the corresponding signal on the

SCSI bus. The signal name followed by a a minus

sign (–) indicates an active-low signal while a plus

sign (+) indicates an active-high signal.

A reset function, which disables all outputs and

clears internal latches, can be accomplished from

two external inputs and two internally generated

signals. RESET (Reset) and DSENS (differential

sense) are available to external circuits for a bus

reset

disable

all

outputs

should

single-ended cable be inadvertently connected to

a differential connector. The power-up and

thermal-shutdown are internally generated sig-

nals that have the same effect when the supply

voltage is below 3.5 V or the junction temperature

exceeds approximately 175

°C.

This data sheet contains descriptions of the

SN75970B input and output signals followed by

the electrical characteristics. The parameter

measurement information is followed by the

theory of operation, a state flow chart, and a

typical circuit in the application information

section.

BATN –

BATN +

BACK –

BACK +

BMSG –

BMSG +

BC/D –

BC/D +

BI/O –

BI/O +

BRST +

BRST –

BBSY +

BBSY –

BSEL +

BSEL –

State Machine and

Control Logic

Oscillator

Thermal

Shutdown

Power-Up

and Reset Logic

DRVBUS

SDB

TIMEOUT

AATN –

AACK –

AMSG –

AC/D –

AI/O –

ARST –

ABSY –

ASEL –

BREQ –

BREQ +

AREQ –

DSENS

TEST

RESET

RSTFLTR

CLK40

X1/CLK20

logic diagram (positive logic)

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