June 1989

DM74184 DM74185A

BCD-to-Binary and Binary-to-BCD Converters

General Description

These monolithic converters are derived from the 256-bit

read only memories DM5488 and DM7488 Emitter con-

nections are made to provide direct read-out of converted

codes at outputs Y8 through Y1 as shown in the function

tables These converters demonstrate the versatility of a

read only memory in that an unlimited number of reference

tables or conversion tables may be built into a system Both

of these converters comprehend that the least significant

bits (LSB) of the binary and BCD codes are logically equal

and in each case the LSB bypasses the converter as illus-

trated in the typical applications This means that a 6-bit

converter is produced in each case Both devices are cas-

cadable to N bits

An overriding enable input is provided on each converter

which when taken high inhibits the function causing all out-

puts to go high For this reason 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

The outputs are of the open-collector type

DM74184 BCD-TO-BINARY CONVERTERS

The 6-bit BCD-to-binary function of the DM74184 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 DM74184 is

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

complement Again in each case one bit of the comple-

ment code is logically equal to one of the BCD bits there-

fore these complements can be produced on three lines

As outputs Y6 Y7 and Y8 are not required in the BCD-to-bi-

nary conversion they are utilized to provide these comple-

ment codes as specified in the function table when the de-

vices are connected as shown

DM74185A 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

(Continued)

Connection Diagram

Order Number DM74184N or DM74185AN

See NS Package Number N16E

TL F 6561 – 1

C1995 National Semiconductor Corporation TL F 6561

RRD-B30M105 Printed in U S A