One of the more famous of these devices is the , a cascadable 4-bit arithmetic logic unit, or ALU. An ALU is the heart of a microprocessor. Registers, instruction decoders, counters, and an arithmetic/logic unit, or ALU. And for decades the , as an all-in-one 4-bit ALU on a chip. This applet demonstrates the TTL-series 4-bit arithmetic-logical unit. It takes 4-bit operands and a carry input and calculates one of 16 logical or

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Fairly soon the LSI level bumped up and I never used them again. An ALU is the heart of a microprocessor, performing its operations.

Inside the vintage ALU chip: how it works and why it’s so strange

This chip provided 741181 arithmetic and logic functions, as well as carry lookahead for high performance. Email required Address never made public. Retrieved 23 April I seem to remember some similar stuff in the high loop of the IFR service monitor, theand had the same one I think. I’m describing the with active-high logic, where a high signal indicates 1, as you’d expect.

Using the chip simplified the design of a minicomputer processor and made it more compact, so it was used in many minicomputers.

Explaining The Operation Of The 74181 ALU

The starting point for the student of microprocessor internals often lies in the past. Views Read Edit View history.


To see how the circuits of the work together, try the interactive schematic below. For example, consider the carry in 741881 bit 2. Thank you so much user WhatRoughBeast. Inside the vintage ALU chip: It would be interesting to scale this to 8 bits though, through in some registers and addressing and see what you get.

You are commenting using your WordPress. Would be nice slu have the original schematic overlaid on silkscreen: The ‘s circuitry can be viewed as an extension of the 74LS83 to support 74118 Boolean functions and to support logical functions by disabling the carry.

The P and G labels on the datasheet are for active-low logic, so with active-high, they are reversed. Thanks for the great write-up! Hacked the root password and had a 16 terminal miniframe computer in the house where I started to learn a Unix. One example of a modern carry lookahead adder is Kogge-Stone. I love these types of builds!

Allard’s Computer Museum Groningen.

But if you look at the chip more closely, there are a few mysteries. Some with a fan out of up to 10 … would be very high bling factor … lots of LEDs. You are commenting using your Twitter account.

Multiple ‘slices’ can be combined for arbitrarily large word sizes. The result is kind of like doing long addition by hand: The implements a 4-bit ALU providing 16 logic functions and 16 arithmetic functions, as the datasheet below shows.


For instance, there will be a carry from bit 0 to bit 1 if P 7411 is set i. Speaking from experience… these posts work just like fly paper for me.

Explaining The Operation Of The ALU | Hackaday

The PCB version of the faithfully follows the original, but with modern 74LVC gates laid out as they would be in the circuit diagram of the chip, and LEDs to show logic state at the different parts of the circuit. Why do s0 and s1 seem backwards? The was used in various minicomputers and other devices beginning in the s, but as microprocessors became more powerful the practice of building a CPU from discrete components fell out of favor and the was not used in any new designs.

I investigated the chip to find out. All of those used the AM family members.

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.