The DM74LS is a 4-bit high speed parallel Arithmetic. Logic Unit (ALU). Controlled by the four Function Select inputs (S0–S3) and the Mode Control input . The 74S 4-bit ALU bitslice resting on a page from the datasheet. The is a bit slice arithmetic logic unit (ALU), implemented as a series TTL. Description: The NTE is an arithmetic logic unit (ALU)/function generator in a Lead DIP type package that has the complexity of 75 equivalent gates on.

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They are in the standard order they should be, counting up in binary. It implements addition, subtraction, and the Boolean functions you’d expect, but why does it provide several bizarre functions such as “A plus A and not B “? For example, consider the carry in to bit 2. Finally, the first carry must have come from somewhere: The result is kind of like doing long addition by hand: It is also sometimes used in ‘hands-on’ college courses, to train future computer architects.

Retrieved from ” https: These 16 functions are selected by the S0-S3 select inputs.

Die photo of the ALU chip. The carry-lookahead logic in the is almost identical to the earlier 74LS83 adder chip.


The S bits on the right select the operation. Higher-order carries have more cases and are progressively more complicated. I seem to remember some similar stuff in the high loop of the IFR service monitor, theand had the same one I think. And why are the logic functions adtasheet arithmetic functions in any particular row apparently unrelated?

This is called the Generate case. Click image for full size.

(PDF) 74181 Datasheet download

Prior to the introduction of thecomputer CPUs occupied multiple circuit boards and even very simple computers could fill multiple cabinets. The P and G outputs in my schematic are reversed compared to the datasheet, for slightly complicated reasons. For instance, there will be a carry from bit 0 to bit 1 if P 0 is set i. And I show how the implements carry lookahead for high speed, resulting in its complex gate structure.

The simple solution is to ripple the carry from one chip to the next, and many minicomputers used this approach. However, the can also be used with active-low logic, where a low signal indicates a 1. To datasheet this, the computes the carries first and then adds all four bits in parallel, avoiding the delay of ripple carry. The metal layer of the die is visible; the silicon forming transistors and resistors is hidden behind it. In addition, a carry either was generated by bit 1 or propagated from bit 0.


This is called the Propagate case since if there is a carry-in, it is propagated to the carry out.

Early minicomputers built Datasheet out of a large number of simple gates. Early minicomputers built ALUs out of a large number of simple gates. Higher-order carries have more cases and are progressively more complicated. It is straightforward to verify that it implements the table above. The study of computer architecture is often an abstract, paper exercise.

This section needs expansion. Multiple ‘slices’ can be combined for arbitrarily large word sizes. The datasheet catasheet the ALU chip shows a strange variety of operations.

(PDF) Datasheet PDF Download – 4 Bit Arithmetic Logic Unit

Comparing to the ‘ datasheet Nat Semi in my case the logic diagram has the P and G outputs swapped compared to your lovely interactive graphic version. Archived from the original on Newer Post Older Post Home. Although overshadowed by the performance of today’s multi-gigahertz bit microprocessors, this was quite impressive when compared to the sub megahertz clock speeds of the early four and eight bit microprocessors.

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