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I hope you really enjoyed writing your first assembly code.

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Now we move on to the second project and this one is switch red off like the name implies there is a

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switch involved.

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So this is an increment over Project 1 and we would press switch one on the microcontroller board to

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turn on the red LCD rather than keeping it on all the time we would have to press search one and keep

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it on.

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So you see we are moving in a step by step manner so you understand the foundation and because the foundations

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are really relevant.

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So for this we would have to learn new up codes.

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So far we've looked at the move code we've looked at the load looked at store and we used it in our

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program we looked at B BRL.

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We've seen the big X LR And we've seen no operation.

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So we would have to add more in order to use the switch in our program.

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So let's look at the new ones.

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So we have up code number 8 C MP This is compare and what this one does is it subtracts the value of

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the second operation from the first.

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Let's take a look at an example.

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Let's say we have C MP our serial number one.

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It compares the value of our serial with number 1.

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And how does this comparison how he knows whether one is greater than the other is true subtraction

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and there is that P E Q And what this one means is branch if equal to zero B Q mostly used with CMB

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instruction.

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So as we said the C and P compares by means of subtraction and after it's performed the subtraction

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and the resource it comes up with is zero.

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Then we can invoke p and q to do something else.

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For example let's say we have our previous example here CMB our 0 Number 1 q l e d 1.

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What this implies is if you compare our zero to the number one and it's equal branch to l eighty one

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and we can think of a leading one as a subroutine somewhere.

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Compare the value of our zero branch to one if resource of course zero.

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Yes and we have our OB code number 10.

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Wow we know 10 ACOs now.

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And trust me there is a lot you can do with these of course alone.

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They are the fundamentals and you have to understand them and know how to use them.

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And I'm glad you do.

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I hope you do.

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I trust you.

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We have to be an E and B and E branch.

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It seemed like it's not set meaning it's not zero and you know the C flag is the Zero flag.

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So if this zero flag is no set price which means you can think of this as the opposite of the P Q The

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BQ said branch if it's equal to zero and a B and E says branch it's not zero exclamation a sign in programming

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implies not so if you see exclamation as zero meaning not zero.

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Branch if not zero.

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So that's the opposite of the B.

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Let's see this example.

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We have delay.

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Let's take this subroutine called DeLay and what DeLay Dallas's first loads.

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One second one second.

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You can think of as a variable into our zero and then subtracts the value one from our zero.

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And I'm sure you have noticed.

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Yeah we have Iris your iris you are one.

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Yes.

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It's like we have we have three operations in the court exam instruction set.

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You can use to upfront and three operations sometimes.

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In fact we can delete this our zero.

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What this are zero is basically doing is that subtract one from our serial and put the value back into

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our zero.

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So it's like our zero equals to our zero minus one.

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That's what it means here.

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This so I assume B as our 0 0 1 subtract one from our as you put it back in.

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And this this is a subroutine called delay and we said b an E delay b e back to the same subroutine

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meaning if it's not zero come back here so you can see this is some sort of account Dow you have and

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finally one second and one second could be as large as let's say the number six million.

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Keep in mind B E S the opposite of the B Q branch if it's equal to zero that's P Q and B and E primes

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if not equal to zero.

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Yes I'm glad you understand remember sea flag is the Zero flag.

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It a set one sea course to zero and not set when sea is in the number.

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So when we saw cracked in any other number it would continue doing it on to sea.

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Of course zero does elegant.

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Let's see.

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Number eleven up no.

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By 11:00 we have the as UBS the subs we just looked at it subtracts and sets flag in a P S.

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Ah yes that's an interesting one.

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We could use issue B as you B as an S you b without the s.

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They both mean subtract but when you have the s after this it means update or sets the flags in the

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AP s are.

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Remember we dealt with the AP s r and you know the AP s our flags like this zero flag that carry flag

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and so on and so forth.

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So if we were just doing a subtraction and we wanted the answer we didn't want to use the outcome for

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something else we could have used SUV with all the s but we want to set the flag to compare with something

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else wanted the outcome to be used in a comparison.

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So we put the s here and what is does is it sets the the AP as our flag.

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And remember the PSR.

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Let's take a look at this example.

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Let's say our zero.

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Course I assume minus our 1 Yes we dealt with this.

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Remember this one sets the flag here and there's a visual aid of the APC are.

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So what this would do is it would set a zero flag and tell us or it would set the negative flag as well

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depending on the outcome at every level of this.

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These flags here are changed because we put this s here.

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Yes the s imply set a PSR flags and you would see when we when we go into more projects you would see

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we might have at plus s here meaning odd and then update the AP as our flag.

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So when you see an S not on instruction it implies update the PSA which means the flags these flags

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here.