Difference between revisions of "CSC103: DT's Notes 1"
| Line 1,271: | Line 1,271: | ||
|- | |- | ||
|style="width: 25%; background-color: white;"| | |style="width: 25%; background-color: white;"| | ||
| + | |||
@0 | @0 | ||
| + | |||
| | | | ||
This line instructs the translator or ''compiler'' that will take this program and generate a list of instructions in memory that it should store the next instructions at '''Address 0'''. Programs always start at 0. | This line instructs the translator or ''compiler'' that will take this program and generate a list of instructions in memory that it should store the next instructions at '''Address 0'''. Programs always start at 0. | ||
|- | |- | ||
| | | | ||
| + | |||
LOD 10 | LOD 10 | ||
| + | |||
| | | | ||
Load the variable at Address 10 into the AC register. Whatever AC's original value, after this instruction it will contain whatever is stored at Address 10. We'll see in a few moments that the number is 2. So AC will contain 2. | Load the variable at Address 10 into the AC register. Whatever AC's original value, after this instruction it will contain whatever is stored at Address 10. We'll see in a few moments that the number is 2. So AC will contain 2. | ||
|- | |- | ||
| | | | ||
| + | |||
ADD 11 | ADD 11 | ||
| + | |||
| | | | ||
Get the variable at Address 11 and add the number found to the number in the AC register. The AC register's value becomes | Get the variable at Address 11 and add the number found to the number in the AC register. The AC register's value becomes | ||
| Line 1,287: | Line 1,293: | ||
|- | |- | ||
| | | | ||
| + | |||
STO 12 | STO 12 | ||
| + | |||
| | | | ||
Store the contents of the AC at Address 12. Since AC contains 5, the number is copied in the variable at Address 12. | Store the contents of the AC at Address 12. Since AC contains 5, the number is copied in the variable at Address 12. | ||
|- | |- | ||
| | | | ||
| + | |||
HLT | HLT | ||
| + | |||
| | | | ||
<br /> | <br /> | ||
| Line 1,299: | Line 1,309: | ||
|- | |- | ||
| | | | ||
| + | |||
| | ||
| + | |||
| | | | ||
<br /> | <br /> | ||
| Line 1,306: | Line 1,318: | ||
|- | |- | ||
| | | | ||
| + | |||
@10 | @10 | ||
| + | |||
| | | | ||
We now indicate to the translator that the next information should be stored starting at a new address, in this case Address 10. | We now indicate to the translator that the next information should be stored starting at a new address, in this case Address 10. | ||
|- | |- | ||
| | | | ||
| + | |||
3 | 3 | ||
| + | |||
| + | |||
| | | | ||
<br /> | <br /> | ||
| Line 1,319: | Line 1,336: | ||
|- | |- | ||
| | | | ||
| + | |||
5 | 5 | ||
| + | |||
| | | | ||
The number 5 should be stored at memory Address 11. Why 11? Because the previous variable was at Address 10. | The number 5 should be stored at memory Address 11. Why 11? Because the previous variable was at Address 10. | ||
|- | |- | ||
| | | | ||
| + | |||
0 | 0 | ||
| + | |||
| | | | ||
This 0 represents the third variable that will hold the sum of the first two variables. We store 0 because we want to have | This 0 represents the third variable that will hold the sum of the first two variables. We store 0 because we want to have | ||
| Line 1,332: | Line 1,353: | ||
|} | |} | ||
| − | <center>[[Image:CSC103FirstAssemblyProgSimul1.jpg| | + | <center>[[Image:CSC103FirstAssemblyProgSimul1.jpg|600px]]</center> |
| − | <center>[[Image:CSC103FirstAssemblyProgSimul2.jpg| | + | |
| − | <center>[[Image:CSC103FirstAssemblyProgSimul3.jpg| | + | The figure above shows the program entered in the ''Program Window'' of the simulator. It is entered simply by typing |
| − | <center>[[Image:CSC103FirstAssemblyProgSimul4.jpg| | + | the information in the window as one would write a paper, or letter. Programs are texts. They are written using a particular |
| − | <center>[[Image:CSC103FirstAssemblyProgSimul5.jpg| | + | coding system (in our case assembly language), and a ''translator'' must be invoked to transform the text into numbers. |
| + | |||
| + | |||
| + | <center>[[Image:CSC103FirstAssemblyProgSimul2.jpg|600px]]</center> | ||
| + | |||
| + | The figure above shows the result of pressing the '''Translate''' button. The translator takes the program, transforms each line into a number, and stores the numbers at different addresses in memory. You should recognize 3 numbers at Addresses | ||
| + | 10, 11, and 12. Yes? | ||
| + | |||
| + | |||
| + | <center>[[Image:CSC103FirstAssemblyProgSimul3.jpg|600px]]</center> | ||
| + | |||
| + | The figure above shows the same information as displayed in the previous image, but this time we have asked the simulator | ||
| + | to show the contents of memory as instructions. The simulator looks at each number in the memory and simply does a reverse translation. The problem for us is that the simulator does not understand our logic. It doesn't know that we divided our program into two separate parts: the instructions and the data, and that they are at different memory location. If we ask | ||
| + | the simulator to display the contents of memory as instructions, it does so, and not only reverse-decodes the instructions correctly into LOD, ADD, STO, and HLT, but it takes all the other numbers and figures out what instructions would | ||
| + | correspond to these numbers, even though our program doesn't have more instructions. So 3 becomes '''ADD 3''', | ||
| + | 5 becomes '''Add 5''' and 0 becomes '''Add 0'''. | ||
| + | |||
| + | <center>[[Image:CSC103FirstAssemblyProgSimul4.jpg|600px]]</center> | ||
| + | <center>[[Image:CSC103FirstAssemblyProgSimul5.jpg|600px]]</center> | ||
Revision as of 20:10, 28 September 2013
--© D. Thiebaut 08:10, 30 January 2012 (EST)
