Should New Hardware Designs Specify CMOS or TTL Compatibility from the Start?

[Physicslearner500039]

Hi All,

I want to understand this, if I go for new hardware design should I make the following decisions at the beginning of the design

1. The design should be CMOS based or TTL based in the sense that all the ICs on the board should be supporting either CMOS or TTL?

2. If I go for CMOS based all the ICs I purchase should be of CMOS family and I need to manually check from the IC number whether it belongs to that family and similarly for TTL based design I should buy all the TTL ICs?

3. In case if I buy ICs in which some are CMOS and some are TTL then I should take care of the interfacing circuitry? (as i believe CMOS and TTL are not directly compatible)

4. And finally for every IC will it be mentioned that it is either from CMOS or TTL family?

These questions are giving me lot of confusion.

Thanks in advance,
Regards,
Satya

 

[yungman]

We still use TTL stuff? Last design I did was all LV CMOS 6 years ago already!

 

[Physicslearner500039]

We still use TTL stuff? Last design I did was all LV CMOS 6 years ago already!

I am sorry, I did not understand what you are trying to say. Are you trying to say that TTL family is no more available and we are using only CMOS?

Thanks and regards,
satya

 

[DragonPetter]

Your main components will be the technology they are - sort of out of your control, and you pick those components for other reasons than their logic level. For example, I would pick a microcontroller based on all of its features, cost, package and almost never consider its logic level (unless it comes with different options or is non standard).

Once that is established, you will have to check every time you interface one IC to another. You need to look at what kind of logic they use and acceptable voltages between one chip's Voh/Vol and another chip's Vih/Vil. A lot of times you can choose the less important ICs to be the same logic as the ICs you have to use. If they do not satisfy the datasheets, then you will need some kind of voltage translator, buffer, or open-collector intermediate circuit to translate the voltage from one level to another. This is just part of the whole process which also includes satisfying timing diagrams or making sure propagation delays are in tolerance.

 

[alphysicist]

I would advise that the decision to use CMOS or TTL should be based on the specific requirements and constraints of your hardware design. Both CMOS and TTL have their own advantages and disadvantages, and it is important to consider these when making a decision.

1. The choice between CMOS and TTL should be made based on the specific needs of your design. CMOS is known for its low power consumption and high noise immunity, while TTL is known for its high speed and low cost. It is not necessary for all ICs on the board to be of the same family, as long as they are compatible with each other and meet the requirements of your design.

2. If you choose to use CMOS, it is recommended to use all CMOS ICs to ensure compatibility and avoid the need for additional interfacing circuitry. The same applies for TTL. However, it is not necessary to manually check the IC numbers as most manufacturers clearly state the type of technology used in their ICs.

3. If you do end up using a mix of CMOS and TTL ICs, then yes, you will need to take care of the interfacing circuitry. This can add complexity and cost to the design, so it is important to carefully consider the trade-offs.

4. Yes, the type of technology used in an IC is usually mentioned in its datasheet or product specifications. It is important to carefully review this information before purchasing ICs for your design.

In summary, the decision to use CMOS or TTL should be based on the specific requirements and constraints of your hardware design. It is important to carefully evaluate the trade-offs and consider the compatibility of ICs before making a decision. Additionally, it is recommended to thoroughly review the datasheets and specifications of ICs before purchasing them for your design.