These monolithic converters are derived from the 256-bit
read only memories, DM5488, and DM7488. Emitter connections
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 illustrated
in the typical applications. This means that a 6-bit
converter is produced in each case. Both devices are cascadable
to N bits.
An overriding enable input is provided on each converter
which when taken high inhibits the function, causing all outputs
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 analogous
to the algorithm:
a. Shift BCD number right one bit and examine each decade.
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 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
conversion, they are utilized to provide these complement
codes as specified in the function table when the devices
are connected as shown.