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hi so what I'd like to do today is give
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you an introduction to the pep8
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simulator that we're going to use for
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running machine language code as well as
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Assembly Language code so the first
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thing we have to do is find the program
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in theory if you follow the directions
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in the uh handout that I gave you it's
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hopefully in a folder on your desktop
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called pep8 13 win so I'm going to go
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into that
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folder and you're going to select the
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pep a.exe
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icon right it's going to ask you to run
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it you're going to run it so when it
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first opens up it's going to be in this
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basically two panel views source code
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and then the architecture here showing
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the registers and you want to be in a
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three panel view so go up here in the
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middle and left click on this three
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panel View and so now you have a source
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code object code assembly listing region
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you have an architecture region showing
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the different registers the accumulator
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the program counter instruction register
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composed of the instruction specifier
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and operand specifier and then your
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memory dump over here on the right
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and just as a note in the future um
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whenever a program calls for input uh
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make sure you have the batch IO tab
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clicked so that's in the Forefront and
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you'll just enter your values
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here you know 40 for whatever values the
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program is looking for okay you don't
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put any commas or anything like that so
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that's the batch iio area all right well
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the first thing you always want to get
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in the habit of doing is going up under
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system left clicking on system and left
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clicking on clear memory and what that
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does is it clears out your memory memory
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remember that all the programs are run
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from memory and so the instructions are
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fetched from memory and then executed so
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by clearing out memory you're making
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sure that you don't have anything
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residual from previous runs and so it
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just kind of a nice
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restart so the first thing that I'm
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going to do is I'm going to I've cleared
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memory system clear memory so now I'm
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going to go down here in the object code
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window and I'm going to type in the
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object code the machine language program
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from the box on page 163 of your book
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and so I'm going to type that in and
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then um so it starts out 5 0 0 and I'm
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going to continue to type that in and so
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I'll be right back after I type it
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in okay now you can see that I've typed
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in the program from that box on page 163
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excuse me and notice that I put a zz at
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the
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end that ZZ doesn't have anything to do
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with the ma machine language itself
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that's simply two symbols that are used
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by this simulator to know where the end
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of the object code is and so it's just
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for use by this particular simulator so
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now I'm going to go up under build left
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click on build and I like to run these
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in debugging mode so I'm going to go to
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load first I'm going to left click on
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load and that's going to load this
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object code into memory and now notice
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if we read across and from
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zero to 7 to 8 using these addresses
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this address is the address in tax of
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the first bite in the row you'll notice
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that our program that's here has simply
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been copied into memory here and it
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wraps around through there all right so
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everything here is directly from here
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and so we've copied our object code into
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memory so now what we want to do is do
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the fetch execute cycle that we learned
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about as far as how a computer actually
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works and so that's all it's going to
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happen now is that the program the
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simulator is going to do the fetch
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decode execute cycle so now as I
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mentioned before I like to run these in
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debugging mode so I'm going to go build
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start debugging object since this is
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object code machine code and you'll
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notice now what's happened is the
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central region here is populated with
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some values and we have a a button here
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single step that we can start to
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click notice that the program counter
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here has hex value of 0o decimal value
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of zero and it's pointing at the first
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three bytes in memory so the those three
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bytes are in blue and they represent the
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instruction that will next be fetched
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and executed so the program counter is
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pointing at the next instruction excuse
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me to be fetched and
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executed so I'm going to click on single
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step and so that first instruction has
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been fetched and is now sitting in the
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instruction specifier and the operand
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specifier you'll notice that over here
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the operand the instruction specifi is
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the first bite so 5 0 notice that when
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we look at the instruction specifier
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here it's showing it in binary but
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you'll notice that 0 1 01 0000 is simply
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5 and hex what's nice about this
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simulator is that on to the right of
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this on the to the right of the
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instruction specifier it's showing the
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Assembly Language version of that
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instruction specifier so character
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output Caro comma I means to Output the
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asky character associated with the value
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that's in the operand specifier this is
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immediate mode I so the asky character
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associated with hex value 48 if we look
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down here in the output panel is H right
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so all this did was fetch that first
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instruction decode it execute it so the
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execution was the character output a an
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asky character to the user using
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immediate
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mode so the hex value the aski value
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associated with the hex value of 48 is H
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all right notice now that the program
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counter is pointing at location 3 X3
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decimal 3 and you'll notice there that
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the next three byes are in blue so
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that's the next instruction that's going
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to be fetched and executed so we single
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step and you'll notice that now the
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program counter is incremented to
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six pointing at the next instruction to
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be fetched and executed the instruction
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that we just fetched is sitting now in
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the instruction specifier the operand
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specifier you'll notice that this
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operand specifier 65 agrees exactly to
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the Opera specifier here here of
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0065
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0065 and again we have our cheat which
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is showing us that this is character
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output immediate mode immediate
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addressing and so now it's putting out
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the asky character associated with hex
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value of 65 which is an e and we can
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continue to step through this program h
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h h o and so notice now that each time
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the program counter incremented by
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three and now it's pointing at location
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um what's that 15 f f f okay F and so
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now it's one more step on this single
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step and it pulls in that 0 instruction
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which we know to be stop and notice it
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went from 15 to 16 and why is that
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because it fetched a one bite
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instruction stop instructions are one
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bytes one by instruction they're unary
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they have no operand specifier
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associated with them and just pointing
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out how the program counters incremented
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right so the program outputed the word
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hello and so uh and it's finished it's
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stopped you'll notice that we no longer
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have the single step button here that we
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can click on and so um that's showing
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how a machine language program is
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entered into the simulator
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loaded and then executed using debugging
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mode and I would just uh stress that
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it's probably the easiest way to do this
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it avoids some of the particular quirks
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that this particular program has now
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once once you've actually gotten a
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program to work or you're in the process
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of trying to work on one you're probably
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going to want to save it so that you can
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load it later and a way to do that is
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just go up under
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file go save in this case object we want
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to save the object because this is
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object code all right and then find the
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file that you want to save it to I'm
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going just go to the
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desktop and I'm going to save it on the
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desktop and you could save it into a
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particular folder if you want I'm just
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going to call this
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test test. PPO leave the extension alone
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click save and so now I have saved this
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object code right here into a file that
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I can now submit as part of my
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assignment to Sakai or I can reload it
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later on by going up under
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file
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open go to my
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[Music]
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desktop find the file down here
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somewhere hopefully there it is left
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click on that left click on
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open and it reloads it all right so
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that's giving you an example of how to
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enter object code into the program
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machine language load it and execute it
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and then save it
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