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.

Author: Yozshushura Meztirn
Country: Nicaragua
Language: English (Spanish)
Genre: Health and Food
Published (Last): 24 June 2006
Pages: 327
PDF File Size: 1.43 Mb
ePub File Size: 4.33 Mb
ISBN: 503-1-31907-273-4
Downloads: 49488
Price: Free* [*Free Regsitration Required]
Uploader: Shaktirg

In this article, I explain that the ‘s set of functions isn’t arbitrary but has a logical explanation. This circuit computes datahseet G generate and P propagate signals for each bit of the ALU chip’s sum.

These 16 functions are selected by the S0-S3 select inputs. The carry from each bit position can be computed from the P and G signals by determining which combinations can produce a carry. The die layout closely matches the simulator schematic above, with inputs at the top and outputs at the bottom. The previous datasheet showed how the P propagate and G generate signals can be used when adding two values. Thus, the carries can be computed in parallel, before the addition takes place.

Datasheet PDF –

Early minicomputers built ALUs out of a large number of simple gates. Why are there 16 possible functions?


It is dataseet sometimes used in ‘hands-on’ college courses, to train future computer architects. Other arithmetic functions take a bit more analysis.

They are in the standard order they should be, counting up in binary. Gordon Bell ; Allen Newell. Early minicomputers built Datasheet datashret of a large number of simple gates. You can help by adding to it. The occupies a historically significant stage between older CPUs based on discrete logic functions spread over multiple circuit boards and modern microprocessors that incorporate all CPU functions in a single component. My earlier article discusses the circuitry in detail, but I’ll include a die photo here since it’s a pretty chip.

Modern processors continue to use carry lookahead, but in more complex forms optimized for long words and efficient chip layout. But if you look at the chip more datazheet, there are a few mysteries. The metal layer of the die is visible; the silicon forming transistors and resistors is hidden behind it.

74181 Datasheet

There are 63 logic gates. Hi Ken, Great blog. Click image for full size. Views Read Edit View history. The previous section showed how the P propagate and G generate signals can be used when adding two values.

The P and G labels on the datasheet are for active-low logic, so with active-high, they are reversed. Students cannot datasheer the inner workings of a datawheet microprocessor, and few discrete-logic machines are open to student inspection.

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

They are in the standard order they datasheet be, counting datasheet in binary. The Boolean logic functions for arithmetic are in a different order than for logical operations, explaining why there’s no obvious connection between the arithmetic and logical functions. The represents an evolutionary step between the CPUs of the s, which were constructed using discrete logic gatesand today’s single-chip CPUs or microprocessors.


As you can see, the carry logic gets more complicated for higher-order bits, but the point is that each carry can be computed from G and P terms and the carry-in. However, the can also be used with active-low logic, where a low signal indicates a 1. There is another explanation of the ‘ here: The was used in various minicomputers and other devices beginning in vatasheet s, but as microprocessors became more powerful the practice of building a CPU from discrete components fell out of favor and catasheet was not datasheet in dataasheet new designs.

The P and G outputs in my schematic are reversed compared to the datasheet, for slightly complicated reasons. This is called the Generate case. In addition, a carry either was generated by bit 1 or propagated from bit 0.