MC74AC259 Datasheet, PDF (1/9 Pages) ON Semiconductor – 8−Bit Addressable Latch

MC74AC259
MC74ACT259
8ĆBit Addressable Latch
The MC74AC259/74ACT259 is a high-speed 8-bit addressable latch designed for
general purpose storage applications in digital systems. It is a multifunctional device
capable of storing single line data in eight addressable latches, and also a 1-of-8
decoder and demultiplexer with active HIGH outputs. The device also incorporates
an active LOW Common Clear for resetting all latches, as well as an active LOW
Enable. It is functionally identical to the ALS259 8-bit addressable latch.
• Serial-to-Parallel Conversion
• Eight Bits of Storage with Output of Each Bit Available
• Random (Addressable) Data Entry
• Active High Demultiplexing or Decoding Capability
• Easily Expandable
• Common Clear
FUNCTIONAL DESCRIPTION
The MC74AC259/74ACT259 has four modes of operation as shown in the Mode
Selection Table. In the addressable latch mode, data on the Data line (D) is written
into the addressed latch. The addressed latch will follow the data input with all non-
addressed latches remaining in their previous states in the memory mode. All latches
remain in their previous state and are unaffected by the Data or Address inputs.
In the one-of-eight decoding or demultiplexing mode, the addressed output will
follow the state of the D input with all other outputs in the LOW state. In the clear
mode all outputs are LOW and unaffected by the address and data inputs. When
operating the MC74AC/ACT259 as an addressable latch, changing more than one
bit of the address could impose a transient wrong address. Therefore, this should
only be done while in the memory mode. The Mode Select Function Table
summarizes the operations of the MC74AC/ACT259.
VCC MR E D Q7 Q6 Q5 Q4
16 15 14 13 12 11 10 9
8-BIT
ADDRESSABLE
LATCH
N SUFFIX
CASE 648-08
PLASTIC
D SUFFIX
CASE 751B-05
PLASTIC
LOGIC SYMBOL
A0
E
D
A1
A2 _{MR Q0 Q1 Q2 Q3 Q4 Q5 Q6 Q7}
12345678
A0 A1 A2 Q0 Q1 Q2 Q3 GND
FACT DATA
5-1