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Welcome to the unsigned and signed data types lecture and this lecture I'm going to explain VHDL unsigned

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and signed data types what is an unsigned data type and unsigned type is declared in the package numeric

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standard and one unsigned data type is there's an array of standard logic which we know a standard logic

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is an individual one or a zero a specific bit and a type unsigned is interpreted as a standard logic

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vector where we have a group of standard logic.

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But the difference is we have different operators available with a of logic vector we have.

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We can actually do addition or subtraction Hovell with the unsigned data type we can if we have to unsigned

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data types we can take and subtract them or add them to each other.

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And also we can manipulate the individual bits which is a major advantage.

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We can only with an unsigned type.

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We can only represent positive numbers.

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We can't represent a negative number.

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So once we get down to zero if we subtract one will still say zero we can't go to a negative one.

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And in the unsigned data type the leftmost bit is the NSB or the most significant bit.

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Let's take a look at an unsigned data type example.

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We have the data class which is a signal we have the signal name which is count.

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Then we have the colon and the data type which in this case is unsigned and HDL is denoted by just unsigned

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and we have the size of the unsigned data type.

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So here we have a data with minus one down to zero.

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So whenever either data with this if our data is a size of 8 we would take 8 minus one so B 7 down to

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zero which would give us a total of 8 bits in our unsigned data type.

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And then we have our.

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So my coin equals to give us our initial value which we have the other is keyword telling us that all

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these bits are set to zero no matter what size.

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For example if we want to have a signal a with an unsigned data type we'll make it three down to zero

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which gives us 4 bits wide and we want to set that value to 13 which would be the binary value of 1

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1 0 1 with your leftmost bit being less inefficient that we Abdus up.

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That gives a value of 13.

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And if we take another signal we'll call signal B.

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I give it an unsigned data type with 3 down to zero which also is an 0 4 bits of one set that night

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of 5 and 0 1 0 1 leftmost bit is the most significant bit.

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And so that is how you would set the initial value of b to 5 now talk about our signed data types these

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are also declared in the package.

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Numeric standard just like the unsigned data types are and as well these are an array of stand who logic

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just like the unsigned data type.

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However the difference between the unsigned versus the signed is that you're signed data types can represent

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negative numbers.

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And the way they're stored are in twos complement form.

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So if you want to represent a negative five depending on the number of bits you specified for your data

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type you'll want to take negative five and the two's complement form and store it inside in the leftmost

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bit just like the unsigned data type is the MSP or the most significant bit.

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Well let's take a look at what a signed data type example looks like.

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We have our data class which is a signal.

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We have our signal name calling count and data type we're specifying assigned and then the size of that

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sign data type.

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How many bits is that signed data type.

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In this case we're saying data wit minus one down to zero.

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So our data with this if we have 8 bits we subtract one gives a 7 down to zero which are give us 8 bit

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number for Assigned data type and then the initial value which we are specifying them all to be zeros

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which is what the others keyword specifies.

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So let's say we have a signal a which is assigned to type signal we'll call it from 3 down to zero.

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So that gives us four bits and we want to have a negative three value.

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So we have to store this in twos complement.

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So that's where we have a 1 1 0 1.

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The leftmost bit is used to signify that it's negative.

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So we know that's a negative 3 and two's complement form.

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Now we want to have a positive five.

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We have our signal B which is assigned to type as well.

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Three down to zero gives us our four bits and we would specify or initial value is 0 1 0 1 and that's

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how you would set assign data type to a value of 5.

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And that is the signed unsigned datatypes lecture.