SN75LBC968

9-CHANNEL BUS TRANSCEIVER

WITH ACTIVE TERMINATION

SLLS179C – APRIL 1994 – REVISED JANUARY 1999

2

POST OFFICE BOX 655303

description (continued)

The communication between the SN75LBC968 and the controller can be accomplished at 3.3-V logic levels

lower-voltage circuit and the 5-V SCSI bus. The SN75LBC968 also removes the need for special I/O buffers

(and associated power dissipation) on the controller itself. The SN75LBC968 must be used with a SCSI

controller with support for Differential SCSI.

The integrated, current-mode, active termination supplies a constant 24 mA of current (TERMPWR) to the bus

when the bus voltage falls below 2.5 V. This makes the next low-to-high (negation) signal transition independent

of the low-level (asserted) bus voltage, unlike voltage-mode terminators. The termination current is provided

through the TE input and from TERMPWR and can be disabled by letting the TE input float or by connecting

Operational termination is present as long as TERMPWR is applied.

The switching speeds of the SN75LBC968 are sufficient to transfer data over the data bus at ten million transfers

and hold times. The device is available in the space-efficient shrink-small-outline package (SSOP) with 25-mil

lead pitch. The SN75LBC968 meets or exceeds the requirements of ANSI X3.131–1994 (SCSI-2) and the

proposed SPI (SCSI-3) standards, and is characterized for operation from 0

°C to 70°C.

logic diagram (positive logic)

31 1B

56

37

35

33

2B

3B

4B

11

10

9

8

7

6

4

2

54

5

Channel 4

Channel 3

Channel 2

4DE/RE

4A

3DE/RE

3A

2DE/RE

2A

1A

TE

50

48

46

5B

6B

7B

24

23

22

21

20

19

Channel 7

Channel 6

Channel 5

7DE/RE

7A

6DE/RE

6A

5DE/RE

5A

29

8B

9B

28

27

26

25

Channel 9

Channel 8

9DE/RE

9A

8DE/RE

8A

CE

1DE/RE

Active Terminator

DE/RE

B

A

Z

H

L

Z

Z

H

Z

Z

Z

Z

H

L

Z

L

B

A

INPUTS

OUTPUTS

H = high level

L = low level

X = irrelevant

Z = high impedance

TERMINATION FUNCTION

OUTPUT

B

INPUT

TE

GND

VTE

Open

Z

24-mA source

Z

CE

Function Tables

L

H

H

H

H

H

H

TRANSCEIVER FUNCTIONS

X

L

L

H

H

L

H

X

X

X

L

H

X

Open

X

L

H

X

X

Open

X