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COMVIEW USERS MANUAL by Rick Nash Load COMVIEW as you would any BASIC program, then simply type RUN to start. At this point you will see the main screen. It consists of two parts. On the top is a window divided into three parts. The upper left window shows the current state of the 6502 registers. The lower left window shows six bytes from any three memory location in the computer. The right window shows the current contents of the hardware stack. At this point, don't worry if you don't understand any of this. It will become clear as we begin to use different features of COMVIEW. The bottom window (Main window) is the business end of COMVIEW. This is where most of the work gets done. Things like the memory command, the assembler and disassembler use this window for data entry and display. At this point, a title message appears in this window. Let us now turn our attention to the MAIN MENU. Press the Commodore key and M simultaneously. --------------- THE MAIN MENU --------------- At this point, the main menu is displayed. Note the characters inside the square brackets. These are the "HOT" keys that are available while this menu is shown. You can either use the UP and DOWN CRSR keys to choose your selection, then press RETURN, or press the hot key for your choice. In the tutorials, we will use the following mnemonics for making menu selections: [MAIN-T] - means press the T hot key on the MAIN menu. Menu items followed by ellipses (...) means that a sub-menu will open. From all but the MAIN menu, the back arrow is used as an escape key. Pressing the escape key will halt almost all operations (except quick trace). Pressing the escape key from a menu, will take you to the previous menu. Some menus offer a "quick" exit key that will zoom to the MAIN menu. This option is clearly marked on menus that support it. The remainder of this manual will describe all of the options and features of COMVIEW. --------------- THE HELP MENU --------------- Pressing [MAIN-H] will present the HELP menu. There are three help screens avaliable: [HELP-G] - Will display a short synopsis of legal keystrokes and general information about COMVIEW. [HELP-I] - Will bring up the instruction set help menu. Select the instruction using the UP, DOWN, LEFT and RIGHT arrow keys. Then press RETURN to enter your choice. A window will open with full information on the chosen instruction. This window offers a ZOOM key (the RETURN key) to zoom to the main menu. [HELP-C] - Brings up the conversion table. This table a consists of five columns: DEC, HEX, BINARY, ASCII and SCREEN CODES. Use this for base conversions or ASCII/SCREEN codes. Active keys are the UP and DOWN CRSR keys and F7, which will move forward one page. Remember: to back out of anything, press the BACK ARROW (COMVIEW escape key). --------------------- FILL MEMORY COMMAND --------------------- Pressing [MAIN-I] will initiate the fill memory command. This command is used to initialize a section of memory to a given value. Note that you can change ANY memory location, including where COMVIEW is residing, so use this command carefully. Three requesters will prompt you for the starting, ending and fill byte. A requester is a white box that appears and asks for user input. Enter the information, and press RETURN, or use the escape key to cancel. After the third requester, the memory will be filled. ------------- PREFERENCES ------------- Pressing [MAIN-P] will show the preferences menu. This menu allows you to set up defaults for the way COMVIEW acts. At this time, only two entries are found on the preferences screen: [PREFS-S] - Will enable/disable screen-swapping. Screen-swapping is covered under the trace command. [PREFS-R] - Will enable/disable repeating keys. This will be noticed on commands such as the MEMORY command [MAIN-M]. Note the parentheses after each item. If a large dot is shown, then the feature is ENABLED, otherwise it is DISABLED. ------------- DISASSEMBLE ------------- The disassemble command [MAIN-D], will show a section of memory in machine language mnemonic form. A requester will ask for the starting address, and then start the disassembler. Active keys are the UP and DOWN CRSR keys (meaning forward and backward scrolling disassembly), and of course the escape key. Note that disassembling a data table will produce garbage mnemonics (watch the ASCII field), but if real ML follows the table, the disassembler will right itself after several bytes. Here is a sample disassembled line: A B C D E ------------------------------ EACD C0 41 CPY #$41 ;-A field a = hexadecimal address b = machine bytes (hex) c = mnemonic disassembly d = operand e = ASCII representation ---------- ASSEMBLE ---------- The assemble [MAIN-A] command allows you to enter machine language mnemonics into memory. Note that this command does not pretend to be a REAL assembler (see ROCK'S ASSEMBLER, published on LOADSTAR #87). Rather, it allows you to quickly and easily enter small chunks of code. It does however offer a few niceties such as limited labels, decimal or hex operands and several pseudo-ops. After entering the address at the requester, you are placed at the main window with the address listed, and a flashing cursor. COMVIEW is waiting for a line of machine code to be entered, such as: LDA #$00 <RETURN> or LDA #0 <RETURN> After pressing RETURN, the line is converted to machine code and inserted into memory. The next address is shown, and the process continues. The DEL key can be used to erase any mistakes before pressing the RETURN key. Errors are flagged by an error window that pops up above the main window. The error is described, and the line is shown with an arrow pointing at the infraction. Pressing C will allow you to continue entering mnemonics. PSEUDO OPS Pseudo ops are mnemonics for the assembler, not the 6502. Three Pseudo's are legal: ORG address - change the current address BYT value - enter the byte (or word) at the current location WOR value - enter the current word (hex or decimal) (note: BYT $1234 and WOR $1234 will produce like output, 34 12) -------- LABELS -------- Limited labels are supported. Use labels only on RELATIVE branch instructions. A minus (-) followed by the character 0-9 for backwards branches, and a plus (+) followed by the character 0-9 for forward branches. For example: LDX #0 -0 TXA CPX #40 BEQ +8 STA $C100,X INX BNE -0 +8 RTS This nonsense code demonstrates the use of forward and backward labels. Note that the + and - are not mathematical, they simply are mnemonic for forwards and backwards. You must keep track of all labels. Since there is no source code, any label that scrolls from the screen will be lost forever, so jot down your labels. Any forward label not referenced will NOT be flagged! This is handled by making the branch point to itself. For example: C020 BNE +5 Will be installed as: C020 BNE $C020 a until the +5 is referenced again. If you forgot to reference it, an endless loop will result. If your program hangs, this is probably why. Consider yourself warned! To stop the assembler, just press the escape key. ---------- REGISTER ---------- The register command [MAIN-R] is used to set the initial value of the .A, .X or .Y registers (register names will be preceded with a period in this manual). When selected, a requester will prompt for a register value. After pressing RETURN, you will notice a highlighted bar over the .A register in the register window on the upper left of your screen. The value shown will be the number you typed in. If you move the bar with the UP or DOWN CRSR keys, note that your number "floats" above the previous register values. Position the bar over the register you want to change, then press RETURN. This places your value into the register. As usual, you can press the escape key to exit without changing any registers. -------- MEMORY -------- Pressing the memory command [MAIN-M], will allow you to enter values directly into any memory location. When selected, you are prompted for an address with the usual requester. The following display will show the main window, with the memory displayed starting at the address you specified. There will be a non-flashing cursor showing your location in memory. Note that there are three fields for each line. The first field is the hex address. The next field shows eight bytes of memory, starting at that address, represented in hex. The last field shows the same eight bytes as represented in ASCII. Non-displayable ASCII such as control codes are shown as periods. You can change any byte by using the cursor keys to move the cursor to the desired byte, and type the hex digit (0-9 and A-F). There is no need to press RETURN to enter the digit. The UP and DOWN CRSR keys will allow you to scroll forward and backward through memory. The F7 key will change fields. If you are on the hex fields, pressing F7 will move the cursor to the ASCII fields. Pressing F7 on the ASCII fields will place the cursor on the hex fields. While on the ASCII field, you can press any key (except of course, the cursor keys and the F7 key). This allows quick entry of ASCII data tables. Press the escape key at any time to quit the memory mode. ------- WATCH ------- The watch command, [MAIN-W] is used to set a watch point. A watch point allows you to watch a memory location during the tracing feature of COMVIEW. The watch window is located directly under the register window at the top of the screen. Three memory locations of six bytes each may be watched. The field layout is the same as the MEMORY command above, except that six bytes are shown instead of eight. Operation is similiar to the register command ([MAIN-R]). After entering the address at the requester, a "floating" bar will allow you to place the desired address at any one of the three possible locations. Press RETURN to make your choice, or escape to quit. ------------- BREAK POINT ------------- The break point is used in conjunction with the QUICK TRACE option [MAIN-Q]. The current breakpoint is shown in the register window at the top of the screen, with the label: BP=. After selecting BREAK POINT, a requester prompts for an address. After pressing RETURN, note that value in the register window should reflect the address that you just entered. See QUICK TRACE for more information on BREAK POINTS. ------- TRACE ------- The TRACE feature [MAIN-T] is the HEART of COMVIEW. It will allow you to execute your program one instruction at a time. After each instruction is executed, the REGISTER, WATCH and STACK windows are updated so that you can see the internal workings of the computer in action. In addition, if screen-swapping is enabled, the alternate screen is swapped in when your instruction executes, and back out when it is done. This feature allows you to use instructions that use the screen without fear of clobbering the COMVIEW screen. It does, however, create unsightly screen flicker. For best performance, be sure to disable screen-swapping (use [MAIN-P] [PREFS-S] to toggle screen-swapping on and off) if your program does not use the screen. If the COMVIEW screen gets written to by accident, use the UPDATE [MAIN-U] command to freshen the COMVIEW display. The F3 key is used to toggle the swapped screens. After answering the address requester when starting the trace mode, the first address is disasembled on the main window. COMVIEW is now waiting for one of three keystrokes. SPACE will execute the instruction shown, then disassemble the next instruction, and the process continues. The J key can be used if the current instruction is a JSR. It will call the routine, and continue execution with the next instruction after the JSR. This is called "stepping over" a call. Alternatively, you could press SPACE at the JSR call, and this is called "stepping through" a call. Do you see the difference? Pressing J at the JSR calls the routine, SPACE will execute each instruction at the JSR address. Note, that for convenience, the J key acts like SPACE for any instruction that is not a JSR. While stepping through the program watch the windows at the top of the screen. You will gain great insight on the actions of the microprocessor. As usual, the escape key will exit the trace function. Note: The tracer may not function on any RS-232 functions. You may find that it chokes on certain KERNAL or ROM calls. This is due to the fact that the NMI interrupt is used for the trace feature. ------------- QUICK TRACE ------------- The quick trace [MAIN-Q] works like the TRACE feature, except that the tracing operation is automatic. That is, you do not press keys to control the tracing action -- it is automatic. Press any of the shifting keys (Commodore, CONTROL, SHIFT or SHIFT LOCK) to pause the display. The STOP key can be used to abort the quick trace at any time. At that point, you will be left in the normal trace mode. This command should be used to skip over unwanted code, to get to a point where you want to trace. WARNING! You MUST use the BREAK POINT [MAIN-B] command BEFORE using the quick trace command! If you ignore this warning, bad things will surely happen. So the sequence of events should be: 1) Set the breakpoint to the address that you want quick trace to stop at (make sure that the address will be executed). 2) Set or clear the screen swap flag if needed. 3) Use QUICK TRACE to execute your program. Follow these steps, and everything will be copacetic! ------ CALL ------ The call command [MAIN-C] allows you to do the equivalent of a SYS (JSR) from the keyboard. After the address requester, your routine will be executed. The screen is swapped if swapping is enabled. The registers, stack and watch windows, reflect their status at the exit from the routine. WARNING! You MUST have an RTS instruction at the end of the code you are executing, or you risk crashing the computer! ---- GO ---- The go [MAIN-G] command executes a program. Execution continues until a BRK instruction. As with the CALL command, screen swapping, register, stack and watch windows are updated. WARNING! The code executed MUST end with a BRK instruction. A crash & burn is a definite possibility if you don't heed this warning! ------ FILE ------ The file command [MAIN-F] will open a sub-menu with the following options: [FILE-S] - Allows you to save your ML programs to disk. Enter the filename, start and end addresses when prompted. [FILE-L] - Use this option to load machine language files from disk. You can relocate while LOADing or, when prompted for an address, you can just press RETURN, and the file will load at the address from where it was saved. [FILE-V] - Will verify that the file on disk is the same as the program in memory. [FILE-D] - Shows the current directory. Press STOP to abort, or one of the SHIFT keys to pause. [FILE-U] - Opens a sub-menu for changing the device number. The current device is always displayed on the main file window. [FILE-E] - Shows the current disk error message. ------------- VIEW OUTPUT ------------- The View Output option [MAIN-V], allows you to examine the current state of the output window. It works like the F3 key during the Trace mode. After viewing the screen, press any key to return to the Main menu. ---------- GLOSSARY ---------- 6502/6510 - The family of microprocessors found in most Commodore computers. ACCUMULATOR - A register located in the microprocessor, where all of the math gets done. On the 6502, the register is named A. ASSEMBLER - A program that converts assembly language mnemonics into machine code. Many other features are usually offered in an assembler to help machine language programmers cope with their task. ASSEMBLY LANGUAGE - Since a microprocessor only understands numbers (see machine language), it would be very tedious for programmers to write machine code programs. So the designers of the chips invented "mnemonics", or three letter words that describe the machine instructions in terms more easily understood by humans. Which makes more sense to you, LDA, or 10101001? It is important that you understand that mnemonics like LDA are completely meaningless to the micro. They are for human consumption only. The list of mnemonics for a given microprocessor is said to be its assembly language. (See assembler). BINARY - A numbering system with a base of 2. Only 1's and 0's are valid in this numbering system. Ex: 101 binary = 5 decimal, 1111 binary = 15 decimal. BIT - One binary digit (0 or 1). BYTE - On the C-64, a byte is eight binary digits (or bits). It can hold a number from 0 (00000000 binary) to 255 (11111111 binary). HEXADECIMAL - A numbering system with a base of 16. The numbers 0-9 represent their decimal equivalent, while A-F represents the numbers 10-15 respectively. Ex: 0A hex = 10 decimal, 10 hex = 16 decimal. K - Short for KILOBYTE, or 1024 bytes. MACHINE LANGUAGE - The native language understood by a microprocessor. Since each memory location can only hold numbers, (0-255), then it seems logical that instructions to the microprocessor must be numerical. It turns out that different numbers instruct the micro to do different tasks. These numbers are called opcodes, and are the "machine language" of a microprocessor such as the 6502. (see assembly language) MEMORY - Special chips located in the computer can hold information. In the C-64, this information is a number from 0 to 255, or a byte. These bytes must be in some kind of order, or else the computer couldn't find bytes that it needs. So, each byte has an "address", the number of addresses is limited by the type of microprocessor installed in the computer. The 6510 in your C-64 can access 64K, or 65536 bytes of memory. The address of each byte is linear, ie. from address 0 to address 65535, and each address can hold a single byte. Some memory is lost when you turn off the computer (RAM), and some will never go away (ROM). Some addresses in your computer are neither RAM nor ROM. This memory is known as I/O registers. These registers allow the computer to communicate with other things like the video display, the sound chip, the disk drive, modems etc. I/O means Input/ Output, or input to the computer, or output to some other device. The microprocessor sees these I/O locations for the most part like RAM. MICROPROCESSOR - The microprocessor, or micro, is the intelligence of the computer. By itself, it is pretty stupid, but add a program, and it really can get some work done fast. For instance, your 6510 in the C-64 is capable of adding two numbers together in around 6 microseconds (thats 6 millionths of a second!), so your micro could add around 167,000 pairs of numbers in just 1 second! The acronym CPU (Central Processing Unit) is sometimes used to mean the same thing as a microprocessor. MICROSECOND - 1 millionth of a second (1/1,000,000 sec) or 1,000 MILLISECONDS. MILLISECOND - 1 thousandth of a second (1/1,000 sec) MNEMONIC - (pronounced knee mon ick) According to my dictionary, a mnemonic is "Aiding or designed to aid the memory". Designers of microprocessors invent mnemonics that briefly describe each machine language instruction. This is used to aid humans in remembering the instruction set of a given microprocessor. For the 6502, all mnemonics are three characters in length, and usually "sound" like the job they do. For example: LDA means load the accumulator (most ML programmers pronounce LDA as LoaD A). Mnemonics are important to humans, not micros. Microprocessors only understand numbers. (see assembly language) OPCODE - An opcode is a number that corresponds to a machine language instruction. For example, 169 is the 6502 opcode for the mnemonic LDA. RAM - Memory in the C-64 that can be read from, and written to. RAM is an acronym for Random Access Memory. REGISTER - A memory location located in the microprocessor. This memory location is not within the 64K of memory of the computer. It can be accessed only by special instructions. ROM - Memory whose contents are permanently the same value. Its value even survives without power. ROM is an acronym for Read Only Memory RN - Acronym for Registered Nurse, Really Nice or, in this case, my initials. Usually placed at the end of text. **** End Of Text ****