Little Man Computer. Copyright 2019 Peter Roberts

Transcription

1 Little Man Computer Copyright 2019 Peter Roberts

2 Table of Contents 1. LMC Introduction Getting Started Macros ClearRam clearsource firstpass formatsource readlmcfile savelmcfile secondpass showlittlemancomputer updatesamples zeroram Environment Security Enabling Macros Worksheets Code RAM Samples Forms Little Man Computer Form CPU Group text boxes Program Counter Instruction Register Accumulator Address Register Source Code group buttons Load Save Update Assemble Select sample code Program group buttons Reset Run Stop Step Computer group buttons Assembler group st Pass nd Pass Format Little Man Computer group Restart Clear Zero Status bar Input prompts Output window Using the workbook Bubble Sort sample Running the model Little Man Computer simulator

3 13. The model CPU Machine code instruction set Visual Basic Developer Ribbon Visual Basic button Project password LMC5 Visual Basic project

4 1. LMC5 Navigation: LMC 5 > Next 1.1. Introduction This workbook consists of three worksheets: 1. Code 2. Ram 3. Samples and a form: Little Man Computer Form There is a close connection between the form and two of the worksheets (called Code and RAM ). The third worksheet (called 'Samples') contains some example programs which can be used to populate the code worksheet for assembling and execution. Navigation: LMC 5 > 1.2. Getting Started This later version of the workbook addresses some minor issues that may have been encountered in previous versions. There are also some improvements and additional features: The form has a slightly different look, with buttons associated with the source code being grouped separately from the program buttons A new button has been added that allows new sample code text files to be added to the Samples worksheet Some of the samples provided have been corrected and improved Prompts for numeric input during the execution of a program can now halt the program by clicking the Cancel button or closing the form (top right-hand X button on the form). Previously it would loop for input which may be undesirable Cells on the Code worksheet will high-light together as the program counter changes It is necessary to enable macros for the correct operation of this workbook. Navigation: LMC 5 > Getting Started > Macros All of the useful Macros that can be listed on the Macros button can be called from the Little Man Computer Form. When the workbook is first opened the macros are protected with a Password, apparent with all the buttons on the macro form disabled except for Run and Cancel. It will be necessary to access the Visual Basic from the Developer tab. 3

5 Navigation: LMC 5 > Getting Started > Macros All of the useful Macros that can be listed on the Macros button can be called from the Little Man Computer Form. When the workbook is first opened the macros are protected with a Password, apparent with all the buttons on the macro form disabled except for Run and Cancel. It will be necessary to access the Visual Basic from the Developer tab. This workbook contains macros; they are protected with a simple password in order to avoid accidental changes. If changes are intended, first click on the Visual Basic button on the Developer tab, which will pop up the Visual Basic project window. In the project explorer window, select the LMC5 project, right-click and in the pop-up, click the LMC5 Properties item. A prompt asking for the LMC5 password pops up. It is suggested that tutors may wish to change the default password before subjecting this workbook to the abuse of students who can be surprisingly adept! Once the correct password has been supplied, the project is exposed; repeat the above steps to access the Properties form. Select the Protection tab to change the password; removing the tick from the box will leave workbook project code unprotected. Macros can be exposed with the intention that students and teachers alike can examine the internal workings on this workbook and perhaps offer suggestions for improvements and report any detected errors to the author of this workbook. Praise and recognition are also acceptable comments. Navigation: LMC 5 > Getting Started > Macros > ClearRam 4 worksheet except this cells in the column that ClearRam is a macro that will empty the cells of the Code

6 Navigation: LMC 5 > Getting Started > Macros > ClearRam ClearRam is a macro that will empty the cells of the Code worksheet except this cells in the column that represents the source code; the corresponding cells of the RAM worksheet will also be cleared. Navigation: LMC 5 > Getting Started > Macros > clearsource clearsource is a macro to clear the cells in the source code column of the Code worksheet Navigation: LMC 5 > Getting Started > Macros > firstpass firstpass is one of a pair of macros used to perform the assembly of the source code; it analyses the source code column of the Code worksheet and populates the label table columns with symbols and their calculated values. It assumes that all instructions of take a single byte (a worksheet cell) and any values are less than 100 (therefore limited to 2 characters). Errors are reported on the status line of the LMC form. Navigation: LMC 5 > Getting Started > Macros > formatsource formatsource is a macro that processes the source code column of the Code worksheet and performs cosmetic work on the text. it will place labels in the first position and align any instructions in the next space leaving a single space with any remaining text aligned after the instructions. Navigation: LMC 5 > Getting Started > Macros > readlmcfile readlmcfile is a macro that will allow a text file assumed to contain source code to be opened and read into the source code column of the Code worksheet. Navigation: LMC 5 > Getting Started > Macros > savelmcfile savelmcfile is a macro to save the code in the source code column of the Code worksheet as a text file which can then be edited using a suitable editor (Notepad, for example). Navigation: LMC 5 > Getting Started > Macros > secondpass secondpass macro is the partner to firstpass. It parses the the source code column of the Code worksheet along with the symbol table and populates the RAM column of the Code worksheet with the appropriate values. The RAM worksheet is also populated to match. 5

7 Navigation: LMC 5 > Getting Started > Macros > showlittlemancomputer showlittlemancomputer is used to display the LMC form Navigation: LMC 5 > Getting Started > Macros > updatesamples updatesamples macro will update the Samples worksheet with the source code from the Code worksheet if a matching title is found, otherwise a new column will be populated and the drop-down Samples list on the LMC form will be rebuilt to include the new item. Navigation: LMC 5 > Getting Started > Macros > zeroram zeroram macro will populate all the cells of the Code worksheet and the RAM worksheets that represent the RAM of the LMC with zeroes. Normally, for increased speed of operation, assemblers will not zero memory before building new programs, but assume that programs will overwrite any required locations as necessary; this may leave some ram locations with undefined values from previous use. Programmers should not assume that just because locations have been allocated to a program that they contain zero. 6

8 Navigation: <Root level> 2. Environment This Excel workbook has been tested on Windows and Mac operating systems. On Windows machines, the workbook has been tested on Excel version 2007, 2010 and in Office 365. On Mac machines, the workbook has been tested in Office

9 Navigation: <Root level> 3. Security Security on Windows and Mac machines behaves differently, but both systems require the user to agree to the workbook macros being given the right to run. Macros need to be enabled, and on the Mac, access needs to be granted to Excel to allow some features to operate correctly; for example, clicking the help button will require Excel to access the associated PDF document which constitutes the user guide. Running the workbook from a network drive (or OneDrive, for example) may require the user to make the document a trusted document; be aware that other users on the network may have access to this file and may tamper with the macros with unpredictable consequences. It is recommended that this document be trusted (click Yes). It is not suggested that the tick-box to allow any network files to be trusted is ticked; the user should be aware when files are being accessed from a network. The important macros can be run from the view tab on the Excel ribbon. The VB Developer's environment can be accessed by using the alt-f11 key combination or from the Developer's tab. The RAM worksheet has been protected (without a password) purely because it assists with navigating the ram cells easier using the arrow keys and also because some of the cells have formulae which should not be edited. This help file can be called by the help button on the Little Man Computer form. It is expected to be either a Windows compiled help file (.chm) or a portable document file (.pdf) and should be located in the same folder as the workbook. The workbook VBproject does have the name of the help file listed in its properties section and this will take preference over the above choices. However, to access this file will require additional security settings which are set on a per-user basis (not a workbook basis) and therefore may not be practical in a classroom environment (neither can this setting be programmed). To change the settings in Excel, the user must navigate to File>Options>Trust Center>Trust Center Settings...>Macro Settings> and then check the box to Trust access to the VBA project object model. 8

10 Navigation: <Root level> 4. Enabling Macros When the spreadsheet is opened, a security message will be displayed indicating that Macros have been disabled. It will be necessary for Macros to be enabled; be aware that, in general, enabling Macros may compromise the security of your machine (viruses and malware can exploit the ability to run Macros automatically). Click the Enable Content button; the macro to display the Little Man Computer will run and pop up a form; this form can be used along-side the spreadsheet. 9

11 Navigation: <Root level> 5. Worksheets Navigation: Worksheets > 5.1. Code The Code worksheet has been designed with six working columns interspersed with empty columns for readability. The first used column is used to hold the source code. the code is written using mnemonics, labels and numbers as necessary. The text in this column can be typed in, imported from or exported to a text file using the supplied macros or from the appropriate buttons on the LMC form; the text can also be formatted for readability. The second and third used columns form a symbol table; this is populated by the first-pass routine of the assembler and used by the second-pass routine of the assembler to populate the RAM model columns. The fourth, fifth and sixth used columns form a representation of the RAM model computer. Values can be entered here manually or automatically by the assembler. Navigation: Worksheets > 5.2. RAM The RAM worksheet is a representation of a computer. It displays 100 cells, each representing a RAM location. Values may be entered into any of the on this worksheet or it can be populated automatically by the assembler. This worksheet has been protected without a password so that navigation is restricted to only the significant cells. There are also some cells with formulae in which should not be changed. 10

12 Navigation: Worksheets > 5.2. RAM The RAM worksheet is a representation of a computer. It displays 100 cells, each representing a RAM location. Values may be entered into any of the on this worksheet or it can be populated automatically by the assembler. This worksheet has been protected without a password so that navigation is restricted to only the significant cells. There are also some cells with formulae in which should not be changed. Navigation: Worksheets > 5.3. Samples The Samples worksheet contains several example programs. Each program is in one column, with the first row of the column being a title which can be the file name used for the export or import. The title is also added to the drop-down list of Sample programs to select. Comments are introduced with a double forward slash (//) and are ignored by the assembler; they can appear anywhere on a line and anything from this point to the end of the line is ignored. 11

13 Navigation: Worksheets > 5.3. Samples The Samples worksheet contains several example programs. Each program is in one column, with the first row of the column being a title which can be the file name used for the export or import. The title is also added to the drop-down list of Sample programs to select. Comments are introduced with a double forward slash (//) and are ignored by the assembler; they can appear anywhere on a line and anything from this point to the end of the line is ignored. 12

14 Navigation: <Root level> 6. Forms Navigation: Forms > 6.1. Little Man Computer Form The form is linked to the workbook and will manipulate the cursor according to which of the worksheets (Code or Ram) has been selected. Perhaps the best for demonstration purposes is to use the worksheet named Code. This form is shown as a mode-less form, meaning that the worksheets can still be used while the form is in view. If the form is ever closed (the top right-hand corner X button), it can be shown by selecting either the Code sheet or the RAM sheet or by clicking the Macros button on the View tab; a new dialogue form opens. Select the macro showlittlemancomputer and click the run button. The form will close if the Samples worksheet is selected, but will re-open when either of the code or RAM worksheets are selected. There is close interaction between the form and the worksheets (Code or RAM). Changing the text in the CPU text boxes will update the Code and RAM worksheets accordingly. Selecting a single cell in the Address, Assembly or RAM columns of the code worksheet will update the Program Counter, Instruction Register and Address Register on the Little Man Computer form to match the appropriate cell contents. A similar behaviour will be exhibited on the RAM worksheet. Navigation: Forms > Little Man C omputer Form > CPU Group text boxes 13

15 Navigation: Forms > Little Man C omputer Form > CPU Group text boxes Navigation: Forms > Little Man C omputer Form > C PU Group text boxes > Program Counter Using the cursor on either the code or RAM worksheets to select a memory address will update the Program Counter (PC). Changing the Program Counter on the form will position the cursor on the appropriate cell in the selected worksheet (code or RAM). The Program Counter on the form can be incremented or decremented by using the arrow keys; the up-arrow key will decrement the Program Counter, while the down-arrow key will increment the Program Counter(this will be more intuitive with the code worksheet in view, as the arrow keys will follow the cells on the worksheet). Navigation: Forms > Little Man C omputer Form > C PU Group text boxes > Instruction Register The instruction register is updated based on the selected memory address on either the code or RAM worksheets. Changing the Instruction Register on the form will update the appropriate cell contents in the selected worksheet (code or RAM); for the code worksheet this will be both the Assembler and the RAM columns. 14

16 Navigation: Forms > Little Man C omputer Form > C PU Group text boxes > Instruction Register The instruction register is updated based on the selected memory address on either the code or RAM worksheets. Changing the Instruction Register on the form will update the appropriate cell contents in the selected worksheet (code or RAM); for the code worksheet this will be both the Assembler and the RAM columns. Navigation: Forms > Little Man C omputer Form > C PU Group text boxes > Accumulator The accumulator text box shows the current contents of the LMC accumulator; the contents of this can be changed or viewed during the running of the LMC program; it is also updated on the RAM worksheet; there is no cell on the Code worksheet representing the accumulator. Navigation: Forms > Little Man C omputer Form > C PU Group text boxes > Address Register The address register is updated based on the selected memory address on either the code or RAM worksheets. Changing the Address Register on the form will update the appropriate cell contents in the selected worksheet (code or RAM); for the code worksheet this will be both the Assembler and the RAM columns. Navigation: Forms > Little Man C omputer Form > Source Code group buttons 15

17 Navigation: Forms > Little Man C omputer Form > Source Code group buttons Navigation: Forms > Little Man C omputer Form > Source C ode group buttons > Load The Load button allows previously generated text files of source code to be quickly loaded into the source code column of the code worksheet. It prompts for the location of the file to be loaded; the file is expected to be a text file with an extension of "*.txt". Navigation: Forms > Little Man C omputer Form > Source C ode group buttons > Save The Save button will generate a text file from the source code column of the code worksheet. It prompts for the location and name of the file to be saved. Navigation: Forms > Little Man C omputer Form > Source C ode group buttons > Update The Update button will update the Samples worksheet with the source code from the Code worksheet. If such code does not exist on the Samples worksheet, a new column is populated, and a new entry is added to the drop-down list on the source code group. 16

18 Navigation: Forms > Little Man C omputer Form > Source C ode group buttons > Update The Update button will update the Samples worksheet with the source code from the Code worksheet. If such code does not exist on the Samples worksheet, a new column is populated, and a new entry is added to the drop-down list on the source code group. Navigation: Forms > Little Man C omputer Form > Source C ode group buttons > Assemble The Assemble button generates the machine code for the source code found in the code worksheet. It populates the label table and the RAM table in the code worksheet and the RAM contents in the RAM worksheet; it will also set the program counter to zero (the first RAM location) and the accumulator to zero ready for program execution. The source code column will be reformatted to make it more easily read. *Note: The ram area is not automatically cleared on assembly; so, if there was a previous (longer) program loaded in ram, there may be remnants in memory (this is typical computer behaviour). The user cannot assume, therefore, that when loading a new program that 'new' ram is necessarily empty or that it contains zero. If the user wishes to clear the memory or make all ram contents zero, there are two buttons on the computer tab for this purpose (the macro can also be found on the Excel developer s tab). The memory can be cleared (or zeroed) and the Assemble can be made again to repopulate the RAM with the object code. Navigation: Forms > Little Man C omputer Form > Select sample code The drop-down list is populated with programs found on the Samples worksheet. If new programs are added to or removed from the Samples worksheet, the list will be updated accordingly. Navigation: Forms > Little Man C omputer Form > Program group buttons 17

19 Navigation: Forms > Little Man C omputer Form > Program group buttons Navigation: Forms > Little Man C omputer Form > Program group buttons > Reset The Reset button will set the program counter to zero (the first RAM location of the LMC program) and clear the accumulator contents (set the accumulator to zero) and clear the output display of the Little Man Computer form. It does NOT reset any used memory locations; if it is necessary to perform a full reset this can be achieved by re-assembling the code (treat this as turning the computer off and on again). Navigation: Forms > Little Man C omputer Form > Program group buttons > Run The Run button will start the LMC program from the current Program Counter position, updating the appropriate registers (Address, Instruction and Accumulator) as it progresses. Navigation: Forms > Little Man C omputer Form > Program group buttons > Stop The Stop button will stop or pause the execution of the LMC program at the end of its current instruction. If a program runs away (say, for example an infinite loop executes) the stop button can be used to interrupt the execution; it can be continued by clicking Run or Step. Navigation: Forms > Little Man C omputer Form > Program group buttons > Step 18

20 Navigation: Forms > Little Man C omputer Form > Program group buttons > Step The Step button will execute a single instruction in the loaded LMC program (the next instruction at the Program Counter location), updating the registers and RAM as necessary. Navigation: Forms > Little Man C omputer Form > Computer group buttons Navigation: Forms > Little Man C omputer Form > C omputer group buttons > Assembler group The assembler in this workbook is a two-pass assembler; on the first pass it scans the sourcecode column of the code worksheet, and identifies all the labels and calculates their values (addresses). The output from the first pass populates the label and value columns of the code worksheet. The second pass of the assembler re-scans the sourcecode column of the worksheet and uses the calculated label values to substitute the label for its value and then populates the Address, Assembler and RAM columns of the code worksheet with the result. Comments can be added the program, introducing them with '//' and can appear anywhere on a line and continue to the end of the line. Blank lines (or cells), however are not permitted, and if they appear in a source code file will be ignored. The assembler is not case-sensitive, so Loop and loop are considered identical labels; also LDA and lda instructions are considered identical. In addition to selecting examples from the drop-down list, the CPU can be programmed by entering numbers representing the instructions directly into memory, by typing into or modifying the assembly language area or by preparing a file containing symbolic instructions which can be loaded into the assembly language area. Click the Assemble button to convert the assembly language to numbers in RAM. 19

21 Navigation: Forms > Little Man C omputer Form > C omputer group buttons > Assembler group The assembler in this workbook is a two-pass assembler; on the first pass it scans the sourcecode column of the code worksheet, and identifies all the labels and calculates their values (addresses). The output from the first pass populates the label and value columns of the code worksheet. The second pass of the assembler re-scans the sourcecode column of the worksheet and uses the calculated label values to substitute the label for its value and then populates the Address, Assembler and RAM columns of the code worksheet with the result. Comments can be added the program, introducing them with '//' and can appear anywhere on a line and continue to the end of the line. Blank lines (or cells), however are not permitted, and if they appear in a source code file will be ignored. The assembler is not case-sensitive, so Loop and loop are considered identical labels; also LDA and lda instructions are considered identical. In addition to selecting examples from the drop-down list, the CPU can be programmed by entering numbers representing the instructions directly into memory, by typing into or modifying the assembly language area or by preparing a file containing symbolic instructions which can be loaded into the assembly language area. Click the Assemble button to convert the assembly language to numbers in RAM. Navigation: Forms > Little Man C omputer Form > C omputer group buttons > Assembler group > st Pass The first pass scans the sourcecode column of the code worksheet and identifies all the labels and calculates their values (addresses). The output from the first pass populates the label and value columns of the code worksheet. Navigation: Forms > Little Man C omputer Form > C omputer group buttons > Assembler group > nd Pass The second pass of the assembler re-scans the sourcecode column of the worksheet and uses the calculated label values to substitute the label for its value and then populates the Address, Assembler and RAM columns of the code worksheet with the result. Navigation: Forms > Little Man C omputer Form > C omputer group buttons > Assembler group > Format The format button will format the source code column of the code worksheet. Navigation: Forms > Little Man C omputer Form > C omputer group buttons > Little Man Computer group Navigation: Forms > Little Man C omputer Form > C omputer group buttons > Little Man C omputer group > Restart 20

22 Navigation: Forms > Little Man C omputer Form > C omputer group buttons > Little Man C omputer group > Restart This button performs the steps that would happen when a computer is restarted; the memory would be cleared and any programs, source code, executable code and data would be cleared. This is demonstrated by leaving the Code worksheet empty (apart from the row headings). Navigation: Forms > Little Man C omputer Form > C omputer group buttons > Little Man C omputer group > Clear This button clears the memory that would be occupied by the executable code and data. All that remains will be the source code. Navigation: Forms > Little Man C omputer Form > C omputer group buttons > Little Man C omputer group > Zero This button populates the RAM cells with zeros. It will be necessary reassemble any code before the program can be executed. Navigation: Forms > Little Man C omputer Form > Status bar The status bar at the bottom of the form will explain the next instruction to be executed or show any error messages as necessary. 21

23 Navigation: <Root level> 7. Input prompts During the execution of the program prompts for input are made using a pop-up Windows Input box; pressing the cancel button or closing the box (top right-hand X button) will stop the program execution. Previously this would loop continuously waiting for a satisfactory response (i.e. a value from 0 to 99). 22

24 Navigation: <Root level> 8. Output window The output window can contain up to four lines each containing 35 characters; once filled the window will scroll (losing any earlier output). 23

25 Navigation: <Root level> 9. Using the workbook The workbook comes pre-loaded with sample source code; this is in the first column of the Code worksheet. The Samples worksheet has many examples which can be selected from the Little Man computer form samples drop-down list. User-defined code can be added to this worksheet; the first row is a title row and this will be added to the drop-down list on workbook opening, from where it can then be selected to populate the source code column of the Code worksheet. Once a selection is made, click the Assemble button to populate the rest of the Code worksheet and also populate the RAM worksheet. Columns C (Label) and D (Value) in this worksheet represent a table populated by the first pass of the assembler to generate values for the labels in the source code column. In the second pass of the assembler, these values are used to convert the source code into machine code in the RAM column (and also to the RAM worksheet). The Address and Assembler columns are a visual aid for the reader for comparison with the original source code. 24

26 Navigation: <Root level> 10. Bubble Sort sample The bubble-sort sample provided has some unusual features probably not to be recommended in modern computer programming standards; it includes some self-modifying code (code that can change itself during its execution) this would generate exceptions in modern computers where data and code are separated (partitioned). This makes it difficult to re-run it without re-assembling it. It also includes an infinite-loop situation; if, during the execution and at the prompts for numeric entry, the same number is repeated, the sort will loop trying to sort two identical numbers. It is for the student to identify and correct this bug. 25

27 Navigation: <Root level> 11. Running the model Select the code worksheet 1. If the Little Man Computer form is not visible, select the Macros button on the view ribbon and select showlittlemancomputer from the list of available macros and click the Run button 2. Select an example program from the drop-down list on the Little Man Computer form 3. Click the Assemble button, which will convert the loaded source code file into machine code in RAM 4. Click the RUN button to start execution; alternatively the STEP button may be clicked to step through the program one instruction at a time. 26

28 Navigation: <Root level> 12. Little Man Computer simulator The Little Man Computer (LMC) is an instructional model of a computer, created by Dr. Stuart Madnick in It models the architecture of a simple computer and has all the basic features. See en.wikipedia.org/wiki/little_man_computer for more information. The web site is an on-line model of LMC (with the endorsement of GCSEcomputing.org.uk); it may require JAVA to be installed for this to operate correctly, and my thanks to Peter for the inspiration for this excel version. 27

29 Navigation: <Root level> 13. The model CPU The original concept was that inside the CPU is a tiny man who runs around executing instructions encoded in a list. Inside the CPU there are: 100 Memory locations (numbered 0 to 99) An Arithmetic Unit to do calculations An Accumulator to store the result of the last operation or calculation A Program Counter to store the address (in memory) of the next instruction to do An Instruction Register to hold the top digit of the instruction read from memory An Address Register to hold the bottom two digits of the instruction read from memory An Input device (via a dialogue box) into which a number can be typed when it's needed An Output device (on the Little Man Computer form) where any numbers output are displayed This workbook is a representation of this model; it is entirely unprotected and is therefore open to inspection (or abuse!). The author is not responsible for any problems if changes are made to the original file. Comments for improvements are welcome and can be addressed to the author via the contact link on the web site The Program Counter holds only 2 digits (0 to 99) and the Accumulator holds 3 digits and a sign (-999 to 999). The Output area on the form holds a certain amount of information in four lines of 35 characters; it will then scroll (and old information is lost). When an instruction is read from memory the top digit is used to decide what to do (a single-digit instruction code); the remaining digits form the associated address. To help us write programs more easily each instruction type is given a mnemonic which the ASSEMBLE function converts to the corresponding code. 28

30 Navigation: <Root level> 14. Machine code instruction set The instructions are: Code Name Description 0 HLT Stop (Little Man has a rest) 1 ADD Add the contents of the memory address to the Accumulator 2 SUB Subtract the contents of the memory address from the Accumulator 3 STA or STO Store the value in the Accumulator in the memory address given DAT This location contains numeric data; no action is taken other than to increment the Program Counter 5 LDA Load the Accumulator with the contents of the memory address given 6 BRA Branch - use the address given as the address of the next instruction 7 BRZ Branch to the address given if the Accumulator is zero 8 BRP Branch to the address given if the Accumulator is zero or positive 9 INP or OUT Input or Output. Take from Input if address is 1, copy to Output if address is 2 9 OTC Output accumulator as a character if address is 22. (Non-standard instruction) Note that the LMC computer cannot tell whether memory locations contain instructions or data. Most modern computers can segment their memory (code and data being partitioned) but there must be a way to distinguish the output from one program from the instructions of another. DAT is a fake instruction to tell the assembler that this location contains data. This implementation allows you to output both numbers (OUT) and characters (OTC). On a real computer you would only have the OTC instruction and the program would have to convert numbers to characters before printing. 29

31 Navigation: <Root level> 15. Visual Basic The LMC5 developer project can be accessed either from using alt-f11 key combination of from the Developer tab. If the developer tab is not visible on the ribbon, use the Excel options (File>Options>) to customise the ribbon and check the box to display the Developer tab. The partial screen shots shown here are taken from Excel 365; follow steps 1 to 5 to show the developer tab on the main ribbon. Navigation: Visual Basic > Developer Ribbon 30

32 Navigation: Visual Basic > Developer Ribbon Click the Visual Basic button With the Developer tab active, click the Visual Basic button to expose the LMC5 Visual Basic project. 31

33 Navigation: Visual Basic > Visual Basic button The Visual Basic button is only available on the Developer tab. Clicking this button will expose the LMC5 VB project window. Navigation: Visual Basic > Project password Click the LMC5 project tree root When the LMC5 project is clicked, a password will need to be supplied in order to view the project code. Supply the appropriate password A password is required to access the LMC5 VB project. The default password as supplied is LMC5. Navigation: Visual Basic > LMC5 Visual Basic project 32 Previous

34 Navigation: Visual Basic > LMC5 Visual Basic project Right-click LMC5 project to access properties To change the password right-click the LMC5 project Select LMC5 properties The LMC5 project properties allows a password to be set, removed or changed 33 Previous

35 Index P Password, 4 34