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4. Basic Usage

4.1 The Emulated Commodore VIC-20

Unlike other VIC20 emulators, Power20 is capable of handling several emulated VIC-20 at one time. The number of concurrent VIC-20s is only limited by the available RAM. To create a new VIC-20 select File/New, and choose how much expansion memory you will need. Choose File/Close (Cmd-W) to close a VIC-20 window no longer needed.

Even so the original VIC-20 did not have a reset button built in, many people built one into their VIC-20. Select File/Reset (Cmd-K) to reset the current VIC-20 window. To force a hard-reset that circumvents the reset-protection of many games press the Option key while selecting File/Reset (or Option-Cmd-K).

To bring the VIC-20 back to a well responsive state, when it is stuck in an endless loop (or something similar), the VIC-20 featured the key combination Stop/Restore. This effect can be obtained in Power20 by selecting File/Stop/Restore (Cmd-R). Again pressing the Option key forces a hard Restore.

To quickly suspend all activity in a VIC-20 window, select File/Freeze (Cmd-F). This will freeze the VIC-20 until File/Freeze is activated again. To indicate the frozen state the window name will be surrounded by dots. This is a very useful feature, if you need to answer the phone or door in the middle of an exciting game. To conserve the current state of an VIC-20 over longer periods of time see also: 4.3 RAM Images.

To create a hardcopy of the current VIC-20 screen, select File/Print (Cmd-P). Depending on your printer you can choose to print either in color or in black/white. To print only a portion of the screen, click&drag the mouse to select the part of the screen that you are interested in. It is often advantageous to first Freeze the VIC-20 (see above), so that the image does not change, before making a selection or hardcopy.

It is also possible to copy the contents of the VIC-20 screen to insert it in a document of an other application. To do this click&drag the mouse to define the area of interest (or select Edit/Select All (Cmd-A) to select the entire screen) and then choose Edit/Cut (Cmd-X) or (equivalently) Edit/Copy (Cmd-C) to copy the selected area. The clipboard will now contain a PICT image of the selected area that can be inserted in any paint program. If the VIC-20s screen was in plain text mode the clipboard will also contain the selected screen area as TEXT, for insertion in a text editor or word processor.

It is also possible to paste text into a Power20 window. This makes it easy to develop a VIC-20 program using your favorite Macintosh editor, and then 'type' it into the VIC-20 via Cut&Paste. Try this with the Emulator detection program in Appendix F.

File/Quit (Cmd-Q) terminates Power20. (Surprise, Surprise).

4.2 Storage Devices

A VIC-20 can be connected to up to four 5.25" floppy disk drives (devices #8-11) and one modified (audio-)cassette tape recorder (device #1) called a Datasette. All these storage devices can be emulated by Power20.

Floppy disks are emulated most precisely using D64, X64 or ZipCoded files (Appendix E.3 , E.4 and E.5). To use a D64, X64 or Zipcode file, it is necessary to 'insert' it in the virtual disk drive using Devices/Disk Drive #x/Insert Floppy Disk.Once it is inserted it can be accessed like on a real VIC-20 using BASIC or assembly language programs. If you are not familiar with VIC-20 BASIC and are just interested in playing games see Section 2.6 to learn the necessary commands. To see what files are already available on the currently mounted disk choose Devices/Disk Drive #x/Display Directory. A window will be opened that shows the names and sizes (in Blocks of 254 Bytes) of all files on the disk. Double-click on a name, and the game will automatically be loaded. To remove a disk from a drive use Devices/Disk Drive #x/Eject Disk. Unlike on a real VIC-20 Power20 will properly close all files before ejecting the disk. Note that Power20 will automatically eject the current disk when a new one is inserted.

To create a new disk select Devices/Disk Drive #x/Create New Floppy Disk. This new disk is already formatted, thus it is not necessary to issue a NEW (format) command before using the disk.

Power20 features two modes of Floppy support. You can either have the Mac simulate the Floppy in PowerPC native code. This is very fast (up to 1000x faster than a real 1541) but some games that use fast loaders or other special tricks of the 1541 will crash as this emulation does not support every single feature. On the other hand you can choose a complete floppy emulation, that will support most of the these games. Unfortunately this complete emulation also emulates the original speed of a 1541 of only about 256 Bytes/second and puts extra stress on the Mac CPU. To switch between these two mode choose Devices/Disk Drive #(8/9)/Complete Floppy 1541 Emulation. Note that the complete emulation is only available on drives 8 and 9 and can only be used with D64, X64 or ZipCoded files, but not with T64 or Lynx files nor Mac Folders that are mounted as floppy disks (see below).

Furthermore it is possible to use a folder on the Macintosh hard disk, as a floppy disk for the VIC-20 and use games in VIC-20 program format (P00, PRG, CBM - see Appendix E.1/E.2). To make a Macintosh folder simulate a floppy disk drive choose: Devices/Disk Drive #x/Attach Hard Disk. Now the Macintosh folder behaves just like a VIC-20 floppy disk. Of course the VIC-20 was not designed with such an option in mind, and some VIC-20-programs, that are tightly coupled with the floppy disk drive, won't run from hard disk. The hard disk will only perform the most basic floppy commands like LOAD/SAVE or OPEN, but the none of the fancy floppy commands (like SCRATCH). This is done on purpose, to make sure that no VIC-20 program can cause serious damage to the Mac hard disk.

Storing lots of VIC-20 program in a single Mac folder tends to create clutter that is hard to keep track of. Furthermore it wastes hard disk space, since every single file requires at least one allocation block (often ≥ 32 KByte on large disks or CD-ROMs) on the Mac hard disk. To make things easier to manage it is possible to pack all those files into one neat ZIP archive, saving disk space and avoiding clutter.
To use a ZIP archive choose Devices/Disk Drive #x/Attach ZIP Archive. Now you can load and run games just like from a folder on your Mac hard disk. Note that you can only read from a ZIP archive - writing is not possible.

It is also possible to mount a T64 tape or Lynx file (see Appendix E.6/E.7 for a description of the file formats) on a disk drive by choosing Devices/ Disk Drive #x/ Mount Tape/Lynx. As with the Mac hard disk only a selection of commands is available.
Also it might seem queer to mount a tape in a disk drive some of the T64 and especially Lynx files that are available on the internet expect to be used on a disk drive.

To emulate the Datasette tape drive Power20 uses T64 and Lynx files (see Appendix E.6/E.7). To 'insert' a T64 or Lynx file in the virtual tape drive select Devices/Tape Drive/Mount Tape (Cmd-T). Just as with Floppy Disk there is an option to create a blank tape image (Devices/Tape Drive/ Create New Tape) and to display the contents of a T64 or Lynx file (Devices/Tape Drive/Display Directory). Note that the file size in a tape directory is give in Bytes rather than Blocks.

In addition to T64 and Lynx files, Power20 can mount raw tape images using the TAP format (see Appendix E.10) on the tape drive (but not the disk drives). TAP files are highly precise representations of the contents of a VIC-20 data tape and can contain data not only in the normal VIC-20 format as it is read and written by routines in the VIC-20 ROM, but also data in special formats that can only be read with the appropriate fastloader. This makes it impossible for Power20 to completely decode the data and transfer it to the VIC-20 RAM at once. Instead it is necessary to run the fastloader on the emulated VIC-20. This makes reading TAP images very slow. Data available in the normal VIC-20 format are available at 50 byte/second, but are understood by Power20 and transfered instantly. Turboload data can be read at 200-500 byte/second (depending on the turbo load algorithm used), so that loading an average game will take several minutes. Usually a TAP image contains not only VIC-20 and Turboload data, but also a generous amount of empty space. Use Power20's Turbo Boost mode (Options/Turbo Boost - Cmd-B) to accelerate the emulated VIC-20 while loading.

To keep an eye on the floppy disk (and hard disk) activity of a VIC-20 select Devices/Drive Status LEDs (Cmd-L; Use Opt-Cmd-L to display the LEDs in all VIC-20 windows). This will cause Power20 to display two symbols per enabled disk drive in the bottom left corner. The first symbols stands for the floppy LED. If it is off (gray) the floppy drive is idle. A green LED indicates a read access, a red LED a write access and a yellow LED stands of an open file without read or write activity. The second symbol indicates the floppy error status; a green check means Ok, a red cross indicates an error. To determine the nature of the error, look at the bottom of the corresponding directory window. You can also use the following sequence of BASIC commands.
10 OPEN 1,8,15
20 INPUT#1, EN$, ER$, TR$, SC$
30 CLOSE 1
40 PRINT EN$, ER$, TR$, SC$

If Complete Floppy 1541 emulation is selected Power20 also displays the track that the floppy head currently uses in the bottom row of the directory window. As loading a file can take quite a while in this emulation mode, it is always reassuring to see the head move from track to track once in a while to know that something is happening.

4.3 File Management

Power20 offers versatile tools for manipulating VIC-20 files, making it easy to convert between the different file formats or to create a custom compilation of favorite games.

To create a new disk select Devices/Disk Drive #x/Create New Floppy Disk. This new disk is already formatted, thus it is not necessary to issue a NEW (format) command before using the disk. Similarly a new tape can be created using Devices/Tape Drive/Create New Tape.

To copy files between two disks or tapes, mount both source and destination on drives of a VIC-20 and display the directories. Then select the files you want to copy with the mouse (use shift click to select ranges of files, and option-click to add/remove single files from your selection) and then drag your selection to the destination drive. You can also copy files from/to directory windows of the Finder.

To delete files, select them as above and drag them to the Finder's trash can. Of course items in the trash can be recovered just as usual.

To rename a file, click on the filename (not on the file size, file type or the space in between) and leave the mouse there. After a short time, the filename will become editable. Please note that the new filename must contain only VIC-20 characters.

In order to ensure consistency for the disk/tape images, Power20 prohibits modifications on devices that are in use by a VIC20-program (i.e. files are open), or when full 1541 emulation is enabled (making it impossible to tell if files are open).

Due to the unstructured content of a raw tape image, it is not possible to use the above methods for managing the files stored on TAP images.

4.4 RAM Images

Power20 provides the possibility to save the current state of the VIC20 to a Macintosh file. Thus it is easy to interrupt a game at any point, save it to disk, try the next level and when it was not successful then simply restore to the saved position.

Note that also also this feature is called a RAM image, it also saves the contents of the CPU registers and the state of the VIC and VIAs. Furthermore it saves the state of all completely emulated 1541 disk drives. Furthermore the tapes and disks that were attached are recovered, if they are again available on the computer. To conserve Mac disk space the disks/tapes do not become part of the RAM image.

To create a RAM Image, select File/Save RAM Image (Cmd-S). To restore it choose File/Load RAM Image (Cmd-O). Note that a new emulator window will automatically be created for the loaded RAM image. Thus it is not necessary to open a new window before loading a RAM image, and it is impossible to destroy the contents of any other currently open window.

4.5 Screen Saver

Power20 can also be used as a screen saver. Use it to run old VIC-20 demos while your Mac is idle or have it display images of VIC-20 game covers and old Commodore ads. Using File/Screen Saver it is possible to choose a delay after that Power20 goes to screen saver mode and choose if Power20 should run demos from RAM images and/or should show GIF/JPEG images, and pick folders from where these should come from. It is also possible to have Power20 change the displayed motive every so often.

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