SN75970B_16 Datasheet, PDF (2/23 Pages) Texas Instruments – SCSI DIFFERENTIAL CONVERTER-CONTROL

SN75970B
SCSI DIFFERENTIAL CONVERTER-CONTROL
SLLS323A – NOVEMBER 1999 – REVISED JANUARY 2000
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 a 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 or to disable all outputs should a
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.
logic diagram (positive logic)
6
AATN –
53
BATN –
52
BATN +
8
AACK –
21
AMSG –
51
BACK –
50
BACK +
38
BMSG –
37
BMSG +
11
AC/D –
47
BC/D –
46
BC/D +
10
AREQ –
49
BREQ –
48 _{BREQ +}
22
AI/O –
27
ARST –
25
ABSY –
23
ASEL –
36
BI/O –
35
BI/O +
30
BRST +
H
29
BRST –
32 _{BBSY +}
H
31
BBSY –
34
BSEL +
H
33
BSEL –
DSENS ³
7
TEST ₂
RESET ₁
RSTFLTR ₄
CLK40
55
X1/CLK20
56
X2
State Machine and
Control Logic
Oscillator
H
19
DRVBUS
20
SDB
9
TIMEOUT
Power-Up
and Reset Logic
Thermal
Shutdown
2
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