5-245

FAST AND LS TTL DATA

10-LINE-TO-4-LINE

AND 8-LINE-TO-3-LINE

PRIORITY ENCODERS

The SN54 / 74LS147 and the SN54/ 74LS148 are Priority Encoders. They

provide priority decoding of the inputs to ensure that only the highest order

data line is encoded. Both devices have data inputs and outputs which are

active at the low logic level.

The LS147 encodes nine data lines to four-line (8-4-2-1) BCD. The implied

decimal zero condition does not require an input condition because zero is

encoded when all nine data lines are at a high logic level.

The LS148 encodes eight data lines to three-line (4-2-1) binary (octal). By

providing cascading circuitry (Enable Input EI and Enable Output EO) octal

expansion is allowed without needing external circuitry.

The SN54 / 74LS748 is a proprietary Motorola part incorporating a built-in

deglitcher network which minimizes glitches on the GS output. The glitch

occurs on the negative going transition of the EI input when data inputs 0 – 7

are at logical ones.

The only dc parameter differences between the LS148 and the LS748 are

that (1) Pin 10 (input 0) has a fan-in of 2 on the LS748 versus a fan-in of 1 on

the LS148; (2) Pins 1, 2, 3, 4, 11, 12 and 13 (inputs 1, 2, 3, 4, 5, 6, 7) have a

fan-in of 3 on the LS748 versus a fan-in of 2 on the LS148.

The only ac difference is that tPHL from EI to EO is changed from 40 to

45 ns.

SN54 / 74LS147

(TOP VIEW)

SN54 / 74LS148

SN54 / 74LS748

(TOP VIEW)

4

5

6

7

8

C

B

GND

D

3

2

1

9

A

VCC NC

14

13

12

11

10

9

1

2

3

4

5

6

7

16

15

8

D

3

2

1

9

A

4

5

6

7

8

C

B

OUTPUT

INPUTS

OUTPUT

INPUTS

OUTPUTS

4

5

6

7

E1

A2

A1 GND

VCC EO GS

3

2

1

0

A0

14

13

12

11

10

9

1

2

3

4

5

6

7

16

15

8

EO

GS

3

2

1

0

A0

4

5

6

7

EI

A2

A1

OUTPUTS

INPUTS

OUTPUT

INPUTS

OUTPUTS

SN54/74LS147

SN54/74LS148

SN54/74LS748

10-LINE-TO-4-LINE

AND 8-LINE-TO-3-LINE

PRIORITY ENCODERS

LOW POWER SCHOTTKY

J SUFFIX

CERAMIC

CASE 620-09

N SUFFIX

PLASTIC

CASE 648-08

16

1

16

1

ORDERING INFORMATION

SN54LSXXXJ

Ceramic

SN74LSXXXN

Plastic

SN74LSXXXD

SOIC

16

1

D SUFFIX

SOIC

CASE 751B-03