DM8898 Datasheet, PDF (1/8 Pages) National Semiconductor (TI) – TRI-STATE BCD to Binary/Binary to BCD Converters

January 1987
DM8898 DM8899 TRI-STATE
BCD to Binary Binary 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
Order Number DM8898N or DM8899N
See NS Package Number N16A
TRI-STATE is a registered trademark of National Semiconductor Corporation
C1995 National Semiconductor Corporation TL F 6593
TL F 6593 – 1
RRD-B30M105 Printed in U S A