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Overview

Epple ][ (the Emulated Apple ][ is a free (as in GPLv3), cross-platform (Windows, Linux, Mac) emulator of the Apple ][ and Apple ][ plus computers from Apple, Inc. It strives for accurate emulation of the original machines, with a few extra features added.

Commands

slot

The slot command inserts a card into a peripheral slot of the emulated Apple.

slot <slot> <card>

slot Slot number, 0 through 7, to insert the card into.

card The type of card to insert into the slot (see cards below):

The slot command inserts a card into a peripheral slot. For example:

slot 0 language

inserts a language card into slot zero. Use empty to remove a card:

slot 0 empty

Note that the emulated Apple should be powered off before inserting or removing cards.

motherboard

The motherboard command configures the emulated Apple’s motherboard RAM chips and strapping block.

motherboard ram   {C|D|E} { 4K | 4096 | 16K | 4116 | - | (other-models) } [...up to 8]
motherboard strap {C|D|E} { 4K | 16K } <base>

The RAM configuration lines represent the rows of chips on the motherboard. The motherboard labels the rows as C, D, and E. Each row has 8 chips, one per bit in a byte. The Apple ][ accepts 4K or 16K chips. You use the ram command to insert (or remove) chips from the sockets. You configure each row’s address range by using a “strapping block” on the original Apple. In the emulator, use the strap command to perform this function. You should strap 4K rows to a 4K range of RAM. You should always assign some RAM to the zero address.

For more information about RAM configuration, see Christopher Espinosa, Apple II Reference Manual (Cupertino, Calif.: Apple Computer, 1978), pp. 70-72.

In the motherboard ram configuration line (other-models) of chips are supported, and will produce different bit patterns at power-on time:

MM5290
MK4116
MCM4116

Example of normal 48K RAM configuration:

ram e 16K
strap e 16K 8000
ram d 16K
strap d 16K 4000
ram c 16K
strap c 16K 0000

Example of 4K, showing how you could specify each chip:

ram e - - - - - - - -
ram d - - - - - - - -
ram c 4K 4K 4K 4K 4K 4K 4K 4K
strap c 4K 0000

Example of 4K at zero address, and 8K at HI-RES page one:

ram e 4K
strap e 4K 3000
ram d 4K
strap d 4K 2000
ram c 4K
strap c 4K 0000

cpu

The cpu command chooses which CPU emulator to run with.

cpu epple2

Valid values are:

epple2 The standard, faster, albeit less accurate, high-level emulator. Works for 99.99% of known cases. This is the default value, used when the cpu command is not present.

visual6502 The emulator based on the algorithm and transistor circuitry from http://www.visual6502.org/. WARNING: this emulator is extremely slow, but absolutely 100% accurate to the original MOS6502.

Note: the CPU cannot be changed in the user interface, only in the configuration file.

import

The import command imports a binary image file into the emulated Apple’s ROMs.

import slot <slot> { rom | rom7 | rombank } <base> <file-path>
import motherboard rom <base> <file-path>

slot Slot number, 0 through 7, of peripheral card to import the binary image into.

base Base address in hexadecimal within the given memory area at which to start loading the binary image.

file-path Path of the binary image to import.

The import command reads the binary image byte-for-byte from the given file-path into an area of ROM in the emulated Apple. You can load into either the motherboard or a card in one of the slots. For a card in a slot, you can choose either the normal ROM, the bank-switched ROM, or the so-called seventh ROM area.

You also have to specify the base address within the specific memory area at which the image file will be loaded. Note that the base address is specified as the offset within the specific memory area, and not necessarily as the actual memory address as seen by the Apple. So for motherboard ROM, for example, specifying a base as 2DED will cause the image to be loaded at offset $2DED in the ROM, which will be addressed by the Apple at memory address $FDED, because motherboard ROM starts at address $D000, and $D000 + $2DED = $FDED.

For peripheral cards, the ROM will be seen at locations $Cs00-$CsFF, where s is the slot number (1 through 7). The seventh ROM can be seen as locations $C800-$CFFF; Jim Sather describes this functionality in Understanding the Apple II, on page 6-4, section The Seventh ROM Chip. The EPPLE ][ emulator handles this processing correctly. A card can also have bank-switched ROM, which will show up at addresses $D000-$FFFF when switched in (stealing that address range from motherboard ROM… see Understanding the Apple II, p. 5-26 The 16K RAM Card).

load

The load command loads a WOZ 2.0 format floppy disk image into one of the emulated disk drives.

load slot <slot> drive <drive> [ <file-path> ]

slot Slot number, 0 through 7, of Disk ][ controller card to load the disk image into.

drive Drive number, 1 or 2, of the disk drive on the controller card to load the disk image into.

file-path Optional path of the disk image to import. If omitted, a dialog box will be presented to select the file to load.

The load command will load a WOZ 2.0 image into a disk drive. Specify the slot that contains a Disk ][ controller peripheral card, and specify which drive number (1 or 2).

note

The floppy disk image MUST be a WOZ 2.0 DISK IMAGE. Other formats (for example, nibble, .nib, DOS order, .do, PRODOS order, .po, .dsk, or anything else) must first be converted to WOZ 2.0 format.

You can use Applesauce to generate such files from original floppy disks. Or you can convert .dsk or .d13 images using DskToWoz2.

unload

The unload command removes a floppy disk image from one of the emulated disk drives.

unload slot <slot> drive <drive>

slot Slot number, 0 through 7, of Disk ][ controller card to which the drive is attached.

drive Drive number, 1 or 2, of the disk drive on the controller card to remove the floppy disk image from.

The unload command removes the disk from the specified slot and drive.

Warning

If the disk has been modified but not saved, the modifications will be DISCARDED.

save

The save command saves changes made on an emulated floppy disk back to the original image file.

save slot <slot> drive <drive>

slot Slot number, 0 through 7, of Disk ][ controller card to which the drive is attached.

drive Drive number, 1 or 2, of the disk drive on the controller card to save.

The save command saves any changes that the emulated Apple ][ has made to the floppy disk image. It is important to note that the emulator operates on the image only in memory, and does not immediately write changes back to the real file. You need to issue the save command in order to write changes back to the file. Note that the emulator will display a asterisk \* next to the file-name of a disk image if it has any unsaved changes.

cassette

The cassette command performs various operations of the emulated cassette tape.

cassette load [ <file-path> ]
cassette rewind
cassette tone
cassette blank <file-path>
cassette save
cassette eject { in | out }

file-path File path of the cassette tape image file, a standard WAVE file.

See below for more information about operating the emulated cassette tape interface.

revision

The revision command specifies which revision of Apple ][ motherboard to use.

revision <rev>

rev Revision number of the motherboard. Currently, only two values make any difference in behavior: 0 or 1.

The revision command chooses which revision of the Apple ][ motherboard to use. The only revisions that make any difference (for now, at least) are 0 or 1. Zero is the original (rare) version of the motherboard, that only had two hi-res colors (green and purple), and always displayed text with green and purple fringes.

Display

The orignal Apple ][s didn’t come with a display. The user needed to use either a standard television or a monitor in order to see the computer’s output. The EPPLE ][ emulates a variety of displays; you can cycle between the different types using F2. There are two major types of displays: televisions and monitors. Monitors generally have higher quality (sharper) displays. The displays show the normal visible area of the NTSC video signal generated by the emulated Apple ][ machine.

Monitors

The emulator provides a color monitor, and a green monochrome monitor. These emulate standard, no-frills NTSC monitors. The most noticeable characteristic of a monitor is the horizontal display of pixels. Monitors react faster than TVs, so two adjacent pixels will not merge together; both will be distinctly visible, with blackness between them. For example, type in the following Applesoft command, then cycle through the display types. The monitors will show thin, vertical, green lines; TVs will show continuous horizontal lines.

GR : COLOR=4 : HLIN 10,20 AT 10

Televisions

Televisions react more slowly to changes in the incoming video signal than monitors do, and as a result, horizontal pixels will merge together, forming a more uniform appearance. EPPLE ][’s television mode emulates the signal decoding circuitry of a real television. This includes separating out the chroma portion of the incoming NTSC video signal using a filter algorithm, and calculating the color to display.

Scan Lines

NTSC displays (TVs or monitors) usually receive signals that are interlaced. However, the Apple ][ doesn’t generate interlaced screens. This causes blank rows between each displayed row of pixels. The EPPLE ][ emulates this behavior, but also allows you to fill in these black rows with a copy of the row above it, for a more continuous display (vertically). Use the F4 key to toggle between these two modes.

Resolution

The Apple ][s are commonly documented as having a resolution of 280x192 pixels, and to an extent this is true. Vertically there are 192 pixels, but since there is no interlacing, it is more accurate to display them with one blank space between each. So the EPPLE ][ has two times 192, or 384, vertical pixels in its display. Horizontally there are 280 pixels, but each could also be shifted right one-half dot, allowing for two times 280, or 560, different horizontal displayable positions. To emulate this, the EPPLE ][ shows each emulated pixel as two pixels wide, and displays an emulated half-dot shift as an actual one pixel shift. So the display area of the EPPLE ][ is 560x384. There is an informational area below and to the right of the emulated display that shows various statistics of the emulator. So the total screen area used by the EPPLE ][ is a standard 640x480 pixels.

Full Screen

The EPPLE ][ can run in either full-screen mode, or within a window. Use the F3 key to toggle between the two.

Informational Area

The area at the bottom and the right of the EPPLE ][ display show various information about the emulator.

Keyboard

The EPPLE ][ emulates the original Apple ][ keyboard. The original Apple ][ keyboard had symbols in different places than current common PC keyboards. For example, Shift-2 on the Apple ][ produces a double quote ", but on a PC keyboard it produces an at-sign @. For ease of typing, the EPPLE ][ emulator does not mimic the positions of the original keys, but rather mimics the symbols on the current PC keyboard. So, for example, if you type Shift-2 on the PC keyboard into the EPPLE ][, it produces an at-sign, as you would normally expect.

The Apple ][ keyboard didn’t produce lower-case letters; neither does the emulator. Also, the Apple couldn’t produce an opening square bracket [, braces {}, vertical bar |, or backslash \. There were no up- or down-arrow keys. You cannot type these into the emulator, either. There are other, unusual, cases that are emulated correctly, as well, such as typing Control in conjunction with a number key simply produces that number. So typing a Control-3 is the same as just typing a 3. Also, typing Shift-Control-2 produces the NUL character (ASCII $80).

The Apple ][ keyboards didn’t automatically repeat typing characters when a key was held down. Instead, the user would hold down the REPT (repeat) key while holding down the key that was to be repeated. On the EPPLE ][, this behavior is emulated, and the F10 key is used as the REPT key.

The Apple ][ had no keyboard buffer (actually, it had a buffer of one character). So if you typed several characters on the keyboard before the currently running program had a chance to read them, they would get lost (only the final character typed would be remembered). This behavior can be toggled on or off in the EPPLE ][. By default, the EPPLE ][ will buffer up any characters you type and deliver them to the emulated machine when it asks for them. However, the Apple program must be written properly to allow this to work. Some Apple ][ programs (like maybe some games) may not work correctly in this respect, so you may want to turn off buffering in these cases. With buffering turned off, the EPPLE ][ accurately emulates the original Apple ][. Use the F12 key to toggle the keyboard buffering. Note that pasting from the clipboard (with the Insert key) will most definitely cause keys to be lost if the keyboard buffer is turned off. So if you have a big Applesoft program in the clipboard and you want to paste it into the EPPLE ][ correctly, make sure the keyboard buffer is on.

Special Keys:

Peripheral Cards

Disk ][ Controller

The Disk ][ Controller card emulates the floppy disk controller card and associated disk drives in the original Apple ][ systems. In the emulator, each card has two drives attached to it, referred to as drive 1 and drive 2. The floppy disks themselves are represented by a nibble image of the contents. The emulator emulates the hardware, but to be of any use, you will need to provide the firmware ROM code.

To use a disk card and drives, add these lines to your epple2.conf file, for example:

slot 6 disk
import slot 6 rom 0 /usr/lib/apple2/dos3x/16sector/controller/disk2.a65

The first line uses the slot command to insert a disk contoller card into slot 6, which is the standard slot used for disk cards. The disk keyword loads the 16-sector P6 ROM (Logic State Sequencer). Alternatively, use disk13 to load the 13-sector P6 ROM (for DOS 3.2 or earlier). The next line uses the import command to load the card’s ROM with the disk controller firmware. This firmware is known as the bootstrap or P5 ROM code. It is seen by the Apple ][ at memory addresses $Cs00-$CsFF, where s is the slot number (so in the common case of the card being in slot 6, the ROM is at $C600-$C6FF). The firmware is copyright by Apple, and is available from the Apple II Library.

You can also load a floppy disk image (nibble format) into the drive, either by putting the load command into the epple2.conf file, or by using the command prompt in the emulator (F5 key). For example, you could load the DOS 3.3 system master into slot 6, drive 1, with this command

load slot 6 drive 1 /usr/lib/apple2/dos3x/16sector/disks/dos330/clean330sysmas.nib

Language

The language card emulates an Apple 16K RAM card, commonly called a Language Card. To use a language card, add this line to your epple2.conf file:

slot 0 language

Note that DOS and ProDOS will make use of a language card only if it is in slot zero.

The language card has RAM at addresses $E000-$FFFF, as well as two banks of RAM at addresses $D000-$DFFF. A program switches between these RAMs and/or the motherboard ROM by using the I/O switches at $C080-$C08F.

The information area of the Epple ][ will show the current state of the language card as follows:

An overview of the I/O switches that control the language card is provided by Jim Sather in Understanding the Apple II, p. 5-30, Table 5.4, as follows:

+==================================================================+
| BANK2   BANK1                 ACTION                  READ?      |
+==================================================================+
|  C080    C088      WRTCOUNT = 0*, WRITE DISABLE      ENABLE      |
|_ C084 _  C08C ___________________________________________________|
| RC081   RC089      WRTCOUNT = WRTCOUNT + 1*          DISABLE     |
|_RC085 _ RC08D ___________________________________________________|
| WC081   WC089      WRTCOUNT = 0*                     DISABLE     |
|_WC085 _ WC08D ___________________________________________________|
|  C082    C08A      WRTCOUNT = 0*, WRITE DISABLE      DISABLE     |
|_ C086 _  C08E ___________________________________________________|
| RC083   RC08B      WRTCOUNT = WRTCOUNT + 1*          ENABLE      |
|_RC087 _ RC08F ___________________________________________________|
| WC083   WC08B      WRTCOUNT = 0*                     ENABLE      |
|_WC087 _ WC08F ___________________________________________________|

   * Writing to expansion RAM is enabled when WRTCOUNT reaches 2.

Firmware

The firmware card emulates a (modified) Apple Firmware card. The firmware card is simply an alternate ROM, at addresses $D000-$FFFF, that is switched using the I/O switches at addresses $C080-$C08F. In order to make use of the firmware card, you will need to load the ROM with a binary image from a file on disk. For example, to insert an Integer BASIC firmware card into the emulator, add these lines to your epple2.conf file:

# Firmware card with Integer BASIC and old Monitor
slot 0 firmware
import slot 0 rombank 1000 /usr/lib/apple2/system/intbasic/intbasic.a65
import slot 0 rombank 2425 /usr/lib/apple2/system/other/other.a65
import slot 0 rombank 2800 /usr/lib/apple2/system/monitor/apple2/monitor.a65

For an Applesoft BASIC firmware card, use these:

# Firmware card with Applesoft BASIC and Autostart Monitor
slot 0 firmware
import slot 0 rombank 0000 /usr/lib/apple2/system/applesoft/applesoft.a65
import slot 0 rombank 2800 /usr/lib/apple2/system/monitor/apple2plus/monitor.a65

Note that the addresses specified in the epple2.conf file for the rombank are based on the beginning of the bank ROM itself. For example, specifying 1000 (which is 1000 hex) represents the final memory address of $E000, because the bank ROM is always based at address $D000.

The idea is that you would load your motherboard with, for example, Applesoft BASIC and the Autostart Monitor ROM (to emulate an Apple ][ plus), and then install a firmware card with Integer BASIC and the old Monitor. Booting with DOS 3.3, then, would allow you to type FP to use Applesoft BASIC, or INT to switch to Integer BASIC.

Note that DOS and ProDOS will make use of a firmware card only if it is in slot zero.

Jim Sather, in Understanding the Apple II, on pages 6-18 through 6-21, explains how to modify a firmware card to allow independent switching of the $F800-$FFFF ROM memory. This area is occupied by the Monitor, so it is primarily intended to allow the user to switch between the old Monitor and the Autostart Monitor, independent of switching between Integer and Applesoft BASIC. The EPPLE ][ firmware card emulates this behavior.

The information area of the EPPLE ][ will show the current state of the firmware card as follows:

Clock

The clock card emulates a ProDOS-compatible real-time clock card for the Apple ][. To use a clock card, you will need to configure the EPPLE ][ to insert one into a slot, typically slot 4. You will also need to load the card with its ROM code, which is provided with the emulator in the clock.a65 file. For example, add this to your epple2.conf file:

slot 4 clock
import slot 4 rom 0 /usr/lib/epple2/cards/clock.a65

Of course you may need to adjust the path for your particular system.

To verify that the clock card is working correctly, you can run the following Applesoft program to retrieve the current time from the clock card and print it. This program assumes the card is in slot 4.

NEW

10 CALL -15360 : REM $C400 SLOT 4 ENTRY POINT
20 A = 512 : REM $0200 INPUT BUFFER
30 C = PEEK(A)
40 IF C < 160 THEN 99
50 PRINT CHR$(C);
60 A = A+1
70 GOTO 30
99 END

RUN

The card returns data (into the GETLN input buffer at $0200) in the following format:

mm,ww,dd,hh,nn,ss,000,yyyy,Time Zone,v

Note that only mm,ww,dd,hh,nn fields are used by ProDOS. The other fields, ss,000,yyyy,Time Zone,v, are an EPPLE ][ extension. Also note that ProDOS was not designed to work for years past 2007, so ProDOS will show the incorrect year, but the other fields will be accurate. I believe patches exist for ProDOS to fix this.

Standard Input

The standard input card doesn’t emulate a real piece of hardware; rather, it reads characters from standard input (stdin) (of the EPPLE ][ emulator).

To use a standard input card, add these lines to your epple2.conf file:

# IN#2 reads from standard input
slot 2 stdin
import slot 2 rom 0 /usr/lib/epple2/cards/stdin.a65

That will insert a stdin card into slot 2, and then load its ROM image into the card. The stdin ROM is provided with the EPPLE ][ distribution.

For example, if you have a stdin card installed in slot 2, start the EPPLE ][ emulator from the command line, and at the Applesoft prompt, type IN#2. Then you can switch back to the command shell, and whatever you type will be fed into the emulated Apple. Use RESET or IN#0 to go back to normal.

Standard Output

The standard output card doesn’t emulate a real piece of hardware; rather, it acts similar to a printer card, but instead of sending characters to a printer, it sends them to standard output (stdout) (of the EPPLE ][ emulator).

To use a standard output card, add these lines to your epple2.conf file:

# PR#1 prints to standard output
slot 1 stdout
import slot 1 rom 0 /usr/lib/epple2/cards/stdout.a65

This will insert a stdout card into slot 1 (which is the typical slot for a printer card), and then load its ROM image into the card. The stdout ROM is provided with the EPPLE ][ distribution.

For example, if you have a stdout card installed, at the Applesoft prompt, type PR#1. Whatever you type next will be echoed to standard output. Type PR#0 to stop echoing.

Cassette Tape Interface

The Apple ][ and Apple ][ plus machines have the ability to save and load binary data to and from cassette tape. The user would attach a standard cassette tape recorder to the jacks on the back of the Apple ][, and use the monitor commands R and W, or the BASIC commands LOAD and SAVE, to read and write data on the cassette tape. The user would have to press the play and/or record buttons on the player at the right time.

The Apple ][ has two cassette ports, CASSETTE IN and CASSETTE OUT. To save a program to tape, the user would attach a cassette recorder to the CASSETTE OUT port, load a blank cassette into the recorder, press RECORD (and PLAY), then on the Apple type SAVE. When finished, the user would press STOP, and eject the tape.

To load a previously saved program from tape, the user would attach the player to the CASSETTE IN port, then load and REWIND the tape. The user would PLAY the tape until the header tone could be heard, then STOP. On the Apple ][ the user would type LOAD and immediately press PLAY on the cassette player. After the file loaded, the user would STOP and eject the tape.

The Epple ][ emulates the cassette interface, using a standard WAVE (PCM) file to hold the recorded portion of the tape. It provides two ports, one for CASSETTE IN and a separate one for CASSETTE OUT. Generally you’ll use only one at a time. Use CASSETTE IN for LOADing a program, or CASSETTE OUT for SAVEing a program.

To load a program from a cassette image WAVE file, use cassette load to put the tape into the cassette player. The tape will automatically rewind and advance to the header tone. Then use the Apple LOAD command to load the program from the tape. If the Apple gives you ERR, that means it could not interpret the WAVE audio correctly. If you want to rewind the tape, you can use the casssette rewind command. Use cassette eject in to close the file.

To save an in-memory program to a cassette tape image WAVE file, use cassette blank <file-path> to put a new blank tape image into the cassette recorder. Then use the Apple SAVE command to record to the tape, and then cassette save to save the WAVE file. Use cassette eject out to close the file.

The emulator will not overwrite existing data in a tape image file.

Commands

cassette load [ <file-path> ]

This loads an existing WAVE file (from the host computer) containing a cassette tape image onto the CASSETTE IN port, in preparation for loading the program from it. If file-path is omitted, a dialog box will be presented to select the file to load. The tape is automatically positioned at the first header tone.

cassette rewind

This command rewinds the tape currently on the CASSETTE IN port. After rewinding the tape, you will typically need to fast-forward to the head tone using the cassette tone command.

cassette tone

If more than one program is stored in one WAVE file, then after loading the first program, you may need to fast-forward to the next header tone. This command will do just that.

cassette blank <file-path>

This creates a new empty file (on the host computer) that represents a cassette tape image, and loads it onto the CASSETTE OUT port, in preparation for saving a program to it. The file must not already exist. The file type should be .wav to indicate a WAVE format file.

cassette save

This command saves the changed tape to the file. Note that the display will show an asterisk * next to the file name if there are unsaved changes that need to be saved.

cassette eject { in | out }

This removes the file from the specified cassette port (CASSETTE IN port, or CASSETE OUT port).

Example of Saving to Tape

Start up the emulator with Applesoft ROMs for this tutorial. Enter a simple Applesoft program, just as an example, that we are going to save to a cassette tape image file.

]NEW

]10 PRINT "HELLO"

]20 END

]LIST

10  PRINT "HELLO"
20  END

]RUN
HELLO

We first need to load a tape image file into the cassette machine. Enter command mode by pressing F5, then make a new tape image file.

command: cassette blank hello.wav

This will create a new, empty tape file image named hello.wav in the current default directory. (We could have specified a full path name for the file if we wanted to place it in a different directory.) Notice that the emulator now displays the name of the tape image file.

Next, we tell Applesoft to save the program to the cassette. For this, we just use the SAVE command. Note that this is not the DOS SAVE command; the DOS command has a file name after SAVE. We just use SAVE with no file name.

]SAVE

It will take 10 seconds or so for it to save. Notice that the current position of the tape is counting up as the Apple saves the program. When it is finished, you need to save the changes to the file. Press F5 and enter the emulator command to save the tape image file.

command: cassette save

Now do a NEW to clear the program, and LIST to prove that it’s gone.

]NEW

]LIST

We can now eject the tape (close the file).

command: cassette eject out

Example of Loading from Tape

To load the saved program (from the previous section) into the Apple again, we will need to first load the tape image file back into the cassette machine. Press F5 to enter command mode and load the image file.

command: cassette load

This will bring up the Open File dialog box. Choose hello.wav file you just saved. Notice the emulator now displays the name of the tape image file, along with the position and length of the tape image. Notice the emulator automatically advances the tape to the first header section.

Next, we tell Applesoft to load the program from the cassette. For this, we just use the LOAD command. Note that this is not the DOS LOAD command; the DOS command has a file name after LOAD. We just use LOAD with no file name.

]LOAD

It will take several seconds for it to load. Notice that the current position of the tape is counting up as the Apple loads the program. When it is finished, the program will be loaded.

]LIST

10  PRINT "HELLO"
20  END

]RUN
HELLO

Paddles

The Epple ][ provides two paddles to the Apple ][ machine. One paddle is controlled by moving the mouse left and right; the other paddle is controlled by moving the mouse up and down. The paddle buttons are emulated by the mouse buttons (left and right click).

In Understanding the Apple II, on page 7-33, Jim Sather describes soldering fixed resistors across a game connector to create two real-time clock references. This is emulated by the Epple ][. Paddle timers 2 and 3 are 100-microsecond and 1-millisecond references, respectively.

Speaker

The Apple ][ could generate sound via a speaker that generated square wave audio. A program could read memory location $C030 to toggle the speaker and generate a click sound.

The Epple ][ emulator will generate sounds from the emulated Apple and send them to the audio device. It generates 8-bit mono sound, with a 20,410 Hz sampling rate.