# Which 4-bit register is better?

Joined Jan 25, 2020
2
Hello,

First time post. I am starting to build an 8-bit computer by following along with Ben Eater's tutorial videos on youtube. However, my end goal is to expand on the project and make several more registers than he did.

Right now I am putting together my supplies and ran across two different options for 4-bit register ICs. I am not sure which one because I am not sure about their differences.

First 4-bit register:
https://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10001&langId=-1&catalogId=10001&productId=46922

Second 4-bit register:
https://www.jameco.com/z/CD4076BE-National-Semiconductor-CMOS-4-Bit-D-Type-Register-DIP-16_1247371.html

The only difference I can really see is the price. The first option is what Ben uses in his tutorial videos. But they are 3 times more money. Not that I'm trying to save a couple dollars here. I just want to figure out their difference and why that translates to an IC that costs 3 times as much as the other.

Thank you for the help!

#### jpanhalt

Joined Jan 18, 2008
8,708
They are different logic families. The 74LS series are low-power Shottcky TTL (transistor transistor logic); the CD4000 are CMOS logic. They differ in voltage switching levels. For example TTL recognizes high as 2.0 V and low as 0,8 V. CMOS is 2/3 VDD and 1/3 VDD. There are other differences and concerns about mixing families. Search on comparison of logic families.

Here's one comparison: https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z000000P9yaSAC

And something more detailed: http://www.ti.com/lit/sg/sdyu001ab/sdyu001ab.pdf

#### dl324

Joined Mar 30, 2015
9,947
Welcome to AAC!
The only difference I can really see is the price.
From what I've seen, Ben Eater's design uses TTL. Unless you know what you're doing, you shouldn't mix CMOS and TTL.

#### Chris65536

Joined Nov 11, 2019
164
I just want to figure out their difference and why that translates to an IC that costs 3 times as much as the other.
Probably because it's the old LS series. Mouser has a CD74HCT173E that is TTL compatible for $0.64/ea or 10 @$0.531/ea.

#### dl324

Joined Mar 30, 2015
9,947
If you intermix TTL and CMOS make sure you use a CMOS variant that has TTL compatible inputs and outputs. HCT is okay while HC is not. Samsung labels some/all of their HCT parts HCTLS.