please help for ic 74381 in vhdl

[maryam2015]

What is g not and p not in 74381? and how i can write them in vhdl?

 

[FvM]

If you want to know about 74381 behavior, read the datasheet. Not clear how the TTL IC is related to a VHDL question. Both pins are outputs, what do you mean with "write them in vhdl"?

 

[maryam2015]

If you want to know about 74381 behavior, read the datasheet. Not clear how the TTL IC is related to a VHDL question. Both pins are outputs, what do you mean with "write them in vhdl"?

I want to write vhdl code for 74381
but i can not writ code for g not and p not
can you help me?

 

[KlausST]

Hi,

Again (like FvM recommended) did you read the 74381 datasheet?

Usually there is a truth table for all outputs. At least an exact description.

Klaus

 

[maryam2015]

Hi,

Again (like FvM recommended) did you read the 74381 datasheet?

Usually there is a truth table for all outputs. At least an exact description.

Klaus

I read datasheet but I do not understand how write the code that explain the IC behavior

 

[KlausST]

Hi,

Why don't you include truth tables in VHDL?

Klaus

 

[Wiljan]

The 74381 datasheet says;
Carry propagate and generate outputs are provided for use with the ’F182 carry lookahead generator for high-speed expansion to longer word lengths. For ripple expansion, refer to the ’F382 ALU data sheet.

Basic if you have a longnumber to calculate and use ripple carry it will take long time and you might know on early stage that the will be carry so you can flag that to the next stage.

If you want it as VHDL you can use eg. Altera Quartus and add in a 74381 and see how it made.

On the other hand if you need to do calculation there are plenty on VHDL arithmetic functions in most FPGA dev tools and also plenty around on the web.

What do you need to calculate?

 

[dpaul]

Does the OP mean to say that he wants to emulate the functionality provided by IC74381 with VHDL?

 

[ads-ee]

Does the OP mean to say that he wants to emulate the functionality provided by IC74381 with VHDL?

I think the OP may have been tasked with a homework assignment to create a VHDL description of the 74381 (I'm sure this is laziness on the instructors part). The trick of this assignment is the carry look ahead feature, that the OP seems to be stuck on.

Read the wiki information on CLA it describes how the G and P signals are generated based on the inputs.
https://en.wikipedia.org/wiki/Carry-lookahead_adder

Don't want to go looking for the 74381 datasheet, so I don't know if it has a logic diagram of the G and P signals.

 

[FvM]

I don't know if it has a logic diagram of the G and P signals.

Yes it has, both logic schematic and truth table.

 

[fouwad]

G is carry generate output, active low
P is carry propagate output, active low

both of these flags will set(low) if carry is generated or propagated. in VHDL you will have to make a logic for them as both of them are outputs.