TLF6593

January 1987

DM8898DM8899 TRI-STATE

BCD to BinaryBinary to BCD Converters

General Description

These circuits are the TRI-STATE versions of the popular

BCD to binary and binary to BCD converters DM74184 and

DM74185A respectively They are derived from the 256-bit

ROM DM8598 Emitter connections are made to provide

direct read out of converted codes at outputs Y8 through

Y1 as shown in the truth tables Both converters compre-

hend the fact that the least significant bits (LSB) of the bina-

ry and BCD codes are logically equal and in each case the

LSB bypasses the converter Thus a 6-bit converter is pro-

duced in each case and both devices are cascadable

An overriding enable input is provided on each converter

which when taken high inhibits the function causing all

outputs to go into the high-impedance state For this rea-

son and to minimize power consumption unused outputs

Y7 and Y8 of the 185A and all ‘‘don’t care’’ conditions of the

184 are programmed high

DM8898 BCD-TO-BINARY CONVERTERS

The 6-bit BCD-to-binary function of the DM8898 is analo-

gous to the algorithm

a Shift BCD number right one bit and examine each dec-

ade Subtract three from each 4-bit decade containing a

binary value greater than seven

b Shift right examine and correct after each shift until the

least significant decade contains a number smaller than

eight and all other converted decades contain zeros

In addition to BCD-to-binary conversion the DM8898 is pro-

grammed to generate BCD 9’s complement or BCD 10’s

complement In each case one bit of the complement code

is logically equal to one of the BCD bits therefore these

complements can be produced on three lines As outputs

Y6 Y7 and Y8 are not required in the BCD-to-binary conver-

sion they are utilized to provide these complement codes

as specified in the function table when the devices are con-

nected as shown

DM8899A BINARY-TO-BCD CONVERTERS

The function performed by these 6-bit binary-to-BCD con-

verters is analogous to the algorithm

a Examine the three most significant bits If the sum is

greater than four add three and shift left one bit

b Examine each BCD decade If the sum is greater than

four add three and shift left one bit

c Repeat step b until the least-significant binary bit is in the

least-significant BCD location

Features

Y

TRI-STATE versions of DM74184 DM74185A

Y

Typical propagation delay 30 ns

Connection Diagram

Dual-In-Line Package

TLF6593 – 1

Order Number DM8898N or DM8899N

See NS Package Number N16A

TRI-STATE

is a registered trademark of National Semiconductor Corporation

C1995 National Semiconductor Corporation

RRD-B30M105Printed in U S A