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<!doctype html>
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<head>
<!--
This Amos Professional Manual is written by asymetrix for the Amiga community and should stay completely FREE FOREVER.
Created 2008. :)
It was created from the original AMOS Professional Manual by Europress Software Ltd.
It has been updated by Fredrik Rambris.
-->
<title>Memory Banks - AMOS Professional Manual</title>
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<section>
<h1>Memory Banks</h1>
<p>This Chapter explains what memory banks are, the sort of information they can hold and how
they are used.</p>
<p>
Any AMOS Professional program can include optional lists of images, audio samples or music
themes. These items are managed by the AMOS Professional system automatically, and they can
be permanently installed as part of your programs. This means that once these items have been
set up, they may be exploited instantly.</p>
<p>
AMOS Professional stores this information in special areas of accommodation known as
memory banks", and these banks can be created by certain accessories such as the Object
Editor, or directly inside a program with the RESERVE command. Memory banks are also
generated as a direct result of certain instructions, such as GET SPRITE and FRAME LOAD.</p>
</section>
<section id="01-memory-bank-numbers-names-and-types">
<h2>Memory bank numbers, names and types</h2>
<p>Every memory bank is assigned its own unique number, ranging from 1 up to 65535. Bank
numbers 1 to 4 are normally reserved for Objects, icons, music and AMAL programs, and the
remaining banks can be used for any information you choose.</p>
<p>
As well as their identification number, most memory banks also have a name, indicating the
type of information that they are holding. Here are some typical names:</p>
<p>
"Sprites" can contain Objects used for Sprite and Bob images.<br>
"Samples" can hold sound samples.<br>
"Music" can store melodies and background music.<br>
"Resource" can store definitions for control buttons and boxes.</p>
<p>There are two main types of memory bank, "data banks" and "work banks".</p>
<p>A <b>data</b> bank is used to hold vital information which must be permanently available for your
programs to use. Data banks are saved along with the program's Basic listings automatically.
This means that once they have been installed, there is no need to worry about them any
further.</p>
<p>A <b>work</b> bank is temporary, and is freshly defined every time that a program is run. Work banks
are totally discarded when programs are saved onto disc.</p>
<p>Memory banks are also organised according to the type of memory that they make use of.</p>
<p>
<b>Fast banks</b> are stored in fast memory, if this type of memory is available. Fast memory cannot be
used for items that need to be accessed by the Amiga's hardware chips, such as Sprites or
samples, but they are fine for AMAL programs or menu definitions.</p>
<p>
<b>Chip banks</b> are reserved using the Amiga's chip memory, and they can be used directly with the
Amiga's own sound and graphics chips. Depending on the model of Amiga in use, there can be
anything between 512k and 2024k of chip Ram at your disposal.</p>
<p>
Here is a list of the most common types of memory bank that will be used with AMOS
Professional programs:</p>
<table>
<thead>
<tr><th>Bank Name</th><th>Items Stored </th><th>Bank Type</th><th>Memory</th><th>Notes</th></tr>
</thead>
<tbody>
<tr><td>Sprites </td><td>Sprite or Bob images </td><td>Permanent</td><td>Chip</td><td>Bank 1 only</td></tr>
<tr><td>Icons </td><td>Icon images </td><td>Permanent</td><td>Chip</td><td>Bank 2 only</td></tr>
<tr><td>Music </td><td>Melodies </td><td>Permanent</td><td>Chip</td><td>Bank 3 only</td></tr>
<tr><td>AMAL </td><td>AMAL progs. and PL table</td><td>Permanent</td><td>Fast</td><td>Bank 4 only</td></tr>
<tr><td>Samples </td><td>audio samples </td><td>Permanent</td><td>Chip</td><td>Bank 5 default</td></tr>
<tr><td>Menu </td><td>menu definitions </td><td>Permanent</td><td>Fast</td><td>any bank</td></tr>
<tr><td>Pic.Pac </td><td>compressed pictures </td><td>Permanent</td><td>Fast</td><td>any bank</td></tr>
<tr><td>Resource </td><td>buttons and dialogues </td><td>Permanent</td><td>Fast</td><td>any bank</td></tr>
<tr><td>Tracker </td><td>Noisetracker music </td><td>Permanent</td><td>Chip</td><td>any bank</td></tr>
<tr><td>Chip Work</td><td>temporary chip workspace</td><td>Temporary</td><td>Chip</td><td>any bank</td></tr>
<tr><td>Fast Work</td><td>temporary fast workspace</td><td>Temporary</td><td>Fast</td><td>any bank</td></tr>
<tr><td>Chip Data</td><td>long-term chip data </td><td>Permanent</td><td>Chip</td><td>any bank</td></tr>
<tr><td>Fast Data</td><td>constant fast data </td><td>Permanent</td><td>Fast</td><td>any bank</td></tr>
</tbody>
</table>
</section>
<section id="02-reserving-a-bank">
<h2>Reserving a bank</h2>
<p>It has already been explained that AMOS Professional allocates certain types of bank
automatically. To create any other required memory bank, they must first be "reserved". The
RESERVE AS command is followed by the type of bank that you want to create, a comma, then
the number of bytes needed for the length of this bank.</p>
<p>If a selected bank already exists, it will be erased to make room for the new definition.</p>
<p>
Allowable <b>bank numbers</b> range from 1 to 65535, but because bank numbers 1 to 4 are already
used internally by the AMOS Professional system, new banks should be reserved using the bank
numbers 5 and above. For users who have upgraded from earlier versions of the AMOS system,
you will have noted the increase in the range of available bank numbers from the original 15.
There are four alternative types of bank that can be reserved, and these will now be explained.</p>
<h3 class="command" id="i-reserve-as-data">RESERVE AS DATA</h3>
<p><i>instruction: reserve a new data bank</i><br>
<b>Reserve As Data</b> bank number,length</p>
<p>
This reserves the selected bank number with the number of bytes specified as its length. Data
banks are <b>permanent</b>, and wherever possible, their memory will be allocated from fast memory,
so this type of bank should <b>not</b> be used for information such as Objects and samples which need
to be accessed directly by the Amiga's hardware chips.</p>
<h3 class="command" id="i-reserve-as-work">RESERVE AS WORK</h3>
<p><i>instruction: reserve a new work bank</i><br>
<b>Reserve as Work</b> bank number,length</p>
<p>This allocates a <b>temporary</b> workspace of the requested length from fast memory, if it is available.</p>
<p>The work data will be erased every time the program is run from the Editor, and it will be
discarded when the listing is saved onto disc. A quick check can be made to see if the data area
has been successfully assigned to fast memory, using the FAST FREE function, like this:</p>
<code class="prefix edit">M=Fast Free : <comment>Rem Give the amount of available FAST memory</comment>
Reserve As Work 10,1000
If M<>Fast Free
Print "The Data has been stored in FAST Ram"
Else
Print "Sorry, there is only CHIP Ram available"
End If
</code>
<h3 class="command" id="i-reserve-as-chip-data">RESERVE AS CHIP DATA</h3>
<p><i>instruction: reserve a new chip data bank</i><br>
<b>Reserve As Chip Data</b> bank number,length</p>
<p>
Use this variation of the RESERVE AS instruction to allocate a <b>permanent</b> area of memory using
Chip Ram. If there is none available, an "Out of Memory" error will be reported. You can obtain
an instant read-out of the remaining chip memory by calling the CHIP FREE function, as
follows:</p>
<code class="prefix edit">CF=Chip Free
Print "Remaining Chip memory = ";CF;" bytes."
</code>
<p>Once a bank has been defined by this command, it will be saved automatically, along with your
AMOS Professional Basic program.</p>
<h3 class="command" id="i-reserve-as-chip-work">RESERVE AS CHIP WORK</h3>
<p><i>instruction: reserve a new chip work bank</i><br>
<b>Reserve As Chip Work</b> bank number,length</p>
<p>
This command allocates the selected block of <b>temporary</b> memory using Chip Ram, and it is often
used with the DOUBLE BUFFERED sampling system, to play samples directly from hard disc.
Here are some typical examples of the different RESERVE AS commands:</p>
<code class="prefix ex">Reserve As Chip Work 10,10000: <comment>Rem 10000 bytes of chip workspace to bank 10</comment>
Reserve As Work 11,5000: <comment>Rem 5000 bytes of fast workspace to bank 11</comment>
Reserve As Chip Data 12,2000 : <comment>Rem 2000 bytes of permanent chip data to bank 12</comment>
Reserve as Data 13,1000 : <comment>Rem 1000 bytes of fast data to bank 13</comment>
</code>
</section>
<section id="03-saving-memory-banks">
<h2>Saving memory banks</h2>
<p>AMOS Professional provides the simplest of instructions for saving memory banks.</p>
<h3 class="command" id="i-save">SAVE</h3>
<p><i>instruction: save one or more memory banks onto disc</i><br>
<b>Save</b> "filename.abk"<br>
<b>Save</b> "filename.abk",bank number</p>
<p>
If a bank has been created using RESERVE, or some screen Objects have been defined with a
command such as GET BOB, the new data can be saved onto a suitable disc in one of two ways.</p>
<p>
When the SAVE command is followed by a string containing a filename, <b>all</b> current memory
banks will be saved into a single large file, bearing that name. The filename can be anything at
all, but it is common practice to add the ".Abk" extension at the end, to remind yourself that this
is an AMOS Professional memory bank. Similarly, an ".Abs" extension is used to indicate a file
containing a group of several memory banks.</p>
<p>By adding an optional bank number after the filename, only that selected bank will be stored in
the named file onto disc.</p>
<p>Here is an example of an instant image-bank generator:</p>
<code class="prefix edit">N=1 : <comment>Rem Set number of first new image to create</comment>
S=1 : <comment>Rem Set size of image*16</comment>
<comment>Rem Create images in bank one</comment>
For G=0 To 4
<comment>Rem Draw the images</comment>
Ink G+1 : Circle S*7,S*7,S*7 : Paint S*8,S*8
Ink 0: Ellipse S*4,S*5,S*1,5*2 : Paint S*4,S*5
Ellipse S*1 0,S*5,S,S*2 : Paint S*10,S*5
Ellipse S*7,S*10,S*5,S*3 : Ellipse S*7,S*9,S*4,S : Paint S*1 1,S*1
Ink G+1 : Bar S*3,S*7 To S*13,S*9
<comment>Rem Now grab them as Objects</comment>
Get Bob G+N,0,0 To S*16-1 ,S*16-1
<comment>Rem Clear them from the screen</comment>
Cls 0,0,0 To S*16,S*16
Next G
F$=Fsel$("*.Abk"," ","Save your images")
<comment>Rem Save Objects in bank 1</comment>
If F$<>0
Save F$,1
End If
</code>
</section>
<section id="04-loading-memory-banks">
<h2>Loading memory banks</h2>
<p>Once saved, memory banks need to be retrieved and loaded, ready for use. AMOS Professional
makes this process very easy too.</p>
<h3 class="command" id="i-load">LOAD</h3>
<p><i>instruction: load one or more banks into memory</i><br>
<b>Load</b> "filename"<br>
<b>Load</b> "filename",bank number</p>
<p>
Remember it has been suggested that memory bank filenames should have the following
extensions, acting as reminders for human eyes, and identification flags for computer searches:</p>
<p>"filename.Abk" to indicate a single AMOS Professional memory bank<br>
"filename.Abs" for a file containing a group of several memory banks.</p>
<p>These identifiers can be very useful when employed with certain instructions, as follows:</p>
<code class="prefix edit"><comment>Rem Load an Object bank from current disc</comment>
Load Fsel$("*.Abk"," ","Load an Object bank")
List Bank : <comment>Rem List bank details on screen</comment>
</code>
<p>
As can be seen, the LOAD command will load the selected memory bank directly from the
appropriate disc file. An optional destination bank number can be added after the filename to be
loaded, but if it is omitted, or given the number zero, data will be re-loaded into the <b>same</b> bank
numbers from which it was originally saved. Any current information in these existing banks
will be completely lost!</p>
<p>
Object and Icon files are treated slightly differently. If the bank number is greater than zero, any
additional images will be added to the end of the existing bank of images.</p>
</section>
<section id="05-saving-and-loading-memory-blocks">
<h2>Saving and loading memory blocks</h2>
<h3 class="command" id="i-bsave">BSAVE</h3>
<p><i>instruction: save an unformatted memory block</i><br>
<b>Bsave</b> file$,start <b>To</b> end</p>
<p>
A block of memory between a specified start and end location can be saved into a specified file
on disc. For example:</p>
<pre>
Bsave "Test",Start(5) To Start(5)+Length(5) : <comment>Rem Save memory bank 5</comment>
</pre>
<p>
The above example would save the data in memory bank number 5 to a suitable disc. The
difference between this file and a file saved as a normal memory bank is that while SAVE causes
a special bank header to be written, containing information about the bank, this header is not
written for a file when BSAVE is used. This means that LOAD cannot be used for this type of
file. It is also not suitable for Object banks.</p>
<h3 class="command" id="i-bload">BLOAD</h3>
<p><i>instruction: load block of binary data into bank or address</i><br>
<b>Bload</b> file$,bank number<br>
<b>Bload</b> file$, address</p>
<p>
The BLOAD instruction loads a file of binary data into memory. It does not alter the data in any
way. To load this data into a memory bank, the bank must first be reserved, otherwise an error
will be generated. Also note that files to be loaded must not be any larger than the reserved
bank, or other areas of memory will be corrupted.</p>
<p>The file of data can also be loaded from disc into a specified address, using BLOAD.</p>
</section>
<section id="06-deleting-memory-banks">
<h2>Deleting memory banks</h2>
<p>During the course of a program, it may be necessary to define temporary memory banks for
specific purposes. For instance, a title screen may need to be enhanced by an animation
sequence or some background music. Since this data would only be needed at the beginning of
the program, it would serve very little purpose to hold it in memory permanently, and the extra
memory space could be better used for additional graphics and sound in the actual program.
AMOS Professional allows you to delete memory banks directly from inside your programs.</p>
<p>The Amiga's memory system is notoriously wasteful, so care should be taken not to overuse this
technique, otherwise although the CHIP FREE and FAST FREE functions may insist that there is
plenty of memory available, you can still run out! If this should happen, it would be necessary to
quit the program and re-start the Amiga, but providing you are aware of the potential problem
and provided that memory banks are kept as small as is practical, all should be well.</p>
<h3 class="command" id="i-erase">ERASE</h3>
<p><i>instruction: clear a single memory bank</i><br>
<b>Erase</b> bank number</p>
<p>
The ERASE command clears the memory space used by the specified bank number, and returns
this memory to the main program, for future use. For example:</p>
<code class="prefix edit">Reserve as Chip Work 5,1000: <comment>Rem Reserve temporary work bank 5</comment>
Print "Free Chip Memory = ";Chip Free
Wait Key
Erase 5
Print "There is now ";Chip Free; "available bytes."
</code>
<h3 class="command" id="i-erase-all">ERASE ALL</h3>
<p><i>instruction: clear all current memory banks</i><br>
<b>Erase All</b></p>
<p>
This command is used to erase all memory banks that are assigned to the current program,
quickly and completely!</p>
<p>
Memory banks allocated to certain types of computer games can often become much larger than
the actual program listings. In this case, it is sensible to store all Objects in separate files on disc,
and only load them into memory when they are specifically needed in the game. This
dramatically reduces the size of program files and makes it very easy to change the Objects
independently of the main routines. It also allows the same Objects to be used for several
different programs.</p>
<p>
In order to exploit this system, all the memory banks used by the program need to be carefully
erased before the program is saved to disc, otherwise masses of useless data could be stored as
part of the program listing. Use the ERASE ALL command carefully to save large amounts of
valuable disc space.</p>
<h3 class="command" id="i-erase-temp">ERASE TEMP</h3>
<p><i>instruction: clear temporary memory banks</i><br>
<b>Erase Temp</b></p>
<p>This instruction is used to erase all of the temporary work banks from the current program. Any
permanent data banks used for holding Sprites, music or samples will be completely unaffected.
For example:</p>
<code class="prefix edit">Reserve As Data 5,1000: <comment>Rem Reserve 1000 bytes of permanent data</comment>
Reserve As Work 6,1000: <comment>Rem Reserve 1000 bytes of temporary workspace</comment>
Reserve As Chip Work 7,2000: <comment>Rem Reserve 2000 bytes of chip memory</comment>
Erase Temp
List Bank
</code>
<h3 class="command" id="i-bank-shrink">BANK SHRINK</h3>
<p><i>instruction: reduce the size of a bank to new length</i><br>
<b>Bank Shrink</b> bank number <b>To</b> length</p>
<p>This instruction does not erase a bank at all, but shrinks it! BANK SHRINK will not work with
Object or Icon banks, but it is used to reduce the length of a previously reserved memory bank
to the specified smaller length. The excess memory will be returned for use by the main program
without complications.</p>
<p>
This feature is very useful if you create a bank by poking it into memory, and wish to save it
with a more suitable size. For example:</p>
<code class="prefix edit">Reserve As Data 10,1000000: <comment>Rem Very large bank</comment>
Poke$ Start(10)-8,"My Bank" : <comment>Rem Rename bank 8 bytes</comment>
Poke$ Start(10),"This is a small bank!" : <comment>Rem Poke some data</comment>
Bank Shrink 10 To 100: <comment>Rem Shrink bank to 100 bytes</comment>
Save "My_Bank.Abk",10
</code>
</section>
<section id="07-swapping-banks">
<h2>Swapping banks</h2>
<h3 class="command" id="i-bank-swap">BANK SWAP</h3>
<p><i>instruction: swap over two memory banks</i><br>
<b>Bank Swap</b> first bank number, second bank number</p>
<p>The BANK SWAP command switches over the memory pointers assigned to a pair of selected
banks, so that the first bank is assigned to the second bank's memory block and the second bank
grabs the locations used by the first.</p>
<p>
Note that the items held in these banks are completely unaffected by this operation, and the
only thing that changes is the number and type of the memory bank to which the items are
assigned.</p>
<p>
BANK SWAP is commonly used in conjunction with Objects, Icons and music banks. For
example, it can be used to instantly flick between the images in an Icon bank and an Object
bank, like this:</p>
<code class="prefix ex">Load "Objects.Abk" : <comment>Rem Please use your own filename</comment>
Load "Icons.Abk" : <comment>Rem Select appropriate filename</comment>
Bank Swap 1,2 : <comment>Rem Banks 1 and 2 normally used for Sprites and Icons</comment>
</code>
<p>Another possibility is to store several different music banks in memory, and swap them as
required.</p>
</section>
<section id="08-listing-banks-on-the-screen">
<h2>Listing banks on the screen</h2>
<h3 class="command" id="i-list-bank">LIST BANK</h3>
<p><i>instruction: list all current banks in memory</i><br>
<b>List Bank</b></p>
<p>
The LIST BANK instruction is used to provide a complete list of all the banks that are available
from the current program. Information about the banks is listed in the following order:</p>
<ul>
<li>The bank number, ranging from 1 to 65536</li>
<li>A single letter indicating the type of bank, with "F" for Fast or "C" indicating Chip Ram.</li>
<li>The name of the bank, held in a string of eight characters. Please note that Object banks are
identified with the letters "Sprite", even though the same images can be used equally well for
Sprites or Bobs.
</li>
<li>The address of the start of the bank in memory, using hexadecimal notation.</li>
<li>The length of the bank in normal decimal format. In the case of "Sprite" or "Icon" banks, the
number of images in the bank will be given instead.
</li>
</ul>
<p>LIST BANK will result in the following sort of report appearing on the screen:</p>
<pre>
1-C- SpritesS:C61298 L:0000005
3-C- Music S:C60E80 L:0001000
6-F- Work S:100000 L:0010000
</pre>
</section>
<section id="09-memory-bank-functions">
<h2>Memory bank functions</h2>
<p>AMOS Professional provides a full range of memory bank functions, which are used to provide
information about the status of available banks.</p>
<h3 class="command" id="fn-length">LENGTH</h3>
<p><i>function: return the length of a memory bank</i><br>
length=<b>Length</b>(bank number)</p>
<p>
The LENGTH function is used to find the size of the bank whose number is specified in
brackets. Normally, this is measured in bytes, but if the bank contains Objects or Icon data, the
number of images in that bank will be given.</p>
<p>A value of zero is returned for any bank that has not been defined. For example:</p>
<code class="prefix edit">Load Fsel$("*.Abk"," ","Load an Object bank") : <comment>Rem Bank 1</comment>
Print "There are ";Length(1);" images available."
</code>
<h3 class="command" id="fn-start">START</h3>
<p><i>function: return the address of a memory bank</i><br>
address=<b>Start</b>(bank number)</p>
<p>
Use the START function to reveal the address of the memory area allocated to a bank, whose
number is specified in brackets. The address will usually remain fixed for the duration of a
program, but it can be changed by a BANK SWAP command.</p>
<p>
If the specified bank number does not exist, AMOS Professional will give a "Bank not reserved"
error report. This can be avoided by checking the status of a bank with the LENGTH function,
like this:</p>
<code class="prefix edit">If Length(N)>0: <comment>Rem give N a suitable bank number</comment>
Print "Address of the bank is ";Start(N)
Else
Print "This bank does not exist!"
End If
</code>
<p>
The FAST FREE and CHIP FREE functions that are used to find the amount of relevant free
memory have already been explained. These should not be confused with the FREE function,
which reports the amount of free memory in the variable area.</p>
</section>
<section id="10-grabbing-accessory-program-memory-banks">
<h2>Grabbing accessory program memory banks</h2>
<p>Any memory banks that are used by an accessory are independent from the main program.
Existing AMOS users will find that the system for grabbing memory banks has been greatly
enhanced for AMOS Professional programmers.</p>
<p>
The PRG UNDER command is used to check whether a program is accessible "under" the
current program, and if all is well, its memory banks can be grabbed for the current program. As
many different programs as memory allows can be run using the PRUN command, and full
details of these commands as well as communication between programs is explained in <a href="11-04-multitasking.html">Chapter
11.4</a>. Here are the available bank-grabbing instructions and functions:</p>
<h3 class="command" id="fn-blength">BLENGTH</h3>
<p><i>function: return the length of a memory bank from a previous program</i><br>
length=<b>Blength</b>(bank number)</p>
<p>
This function is used to get the length of the specified bank number from a previous AMOS
Professional program, if this is possible. A value of zero will be returned if the specified bank has
not been defined in the previous program, or if there is no previous program accessible at all
(PRG UNDER= 0).</p>
<h3 class="command" id="fn-bstart">BSTART</h3>
<p><i>function: return the address of a memory bank from a previous program</i><br>
address=<b>BSTART</b>(bank number)</p>
<p>Similarly, the BSTART function will give the address of the specified memory bank from a
previous program, if possible. An error will be returned if no such bank has been reserved.</p>
<h3 class="command" id="i-bgrab">BGRAB</h3>
<p><i>instruction: grab a memory bank used by the previous program</i><br>
<b>Bgrab</b> bank number</p>
<p>
This command is used to grab a memory bank from the previous program. The selected bank is
<b>erased</b> from its former program and appropriated to the current program's list of memory
banks. If a selected bank number already exists in the current program, then it will be erased
before being replaced by the grabbed bank. However, a grabbed bank is not automatically
replaced at its original location. This must be achieved using a BSEND instruction, which is
explained next.</p>
<p>
If the bank which is specified to be grabbed does not exist a "Bank not reserved" message will be
generated.</p>
<h3 class="command" id="i-bsend">BSEND</h3>
<p><i>instruction: transfer a memory bank from the current program to the previous program</i><br>
<b>Bsend</b> bank number</p>
<p>
This command is the exact opposite of the BGRAB instruction. The specified bank is erased from
the current program list of banks, and appears in the list of banks belonging to the previous
program. If a bank already occupies this position in the previous program, it will be erased. Both
the BGRAB and BSEND commands are very fast, and blocks of data are not reserved first.</p>
<p>
Here is an example of how to grab memory banks safely. The example lists all of the banks of the
previous program before they are grabbed, and it should be noted that the name of the bank is
located eight bytes before the BSTART address:</p>
<code class="prefix ex">If Prg Under : <comment>Rem Check availability of a previous program</comment>
For B=1 To 1000: <comment>Rem Check the first 1000 banks!</comment>
If Blength(B)
Print "Bank number:";B;" found. Name: ";Peek$(Bstart(B)-8,8)
Bgrab B: <comment>Rem Grab the bank</comment>
End If
Next
End If
</code>
</section>
<section id="11-automatic-bank-grabbing">
<h2>Automatic bank grabbing</h2>
<p>This feature is a unique bonus! It allows memory banks to be passed between programs
completely automatically. You could be in the middle of writing an arcade game, call up the</p>
<p>
Object Editor, change the Bobs in the game, and return to the creation of your program routines
bringing the new Bobs with you!</p>
<p>
No loading and saving are necessary, everything is handled by AMOS Professional, and your
working life is made that much easier! An example of this technique is featured in <a href="13-02-object-editor.html#05-the-grabber">Chapter 13.2</a>.</p>
</section>
<section id="12-creating-your-own-utilities">
<h2>Creating your own utilities</h2>
<p>The following functions are provided in order to provide developers with full access to the inner
workings of the AMOS Professional system. They are definitely not intended for the casual
programmer, but they do allow advanced users to create customised AMOS Professional
utilities.</p>
<h3 class="command" id="fn-screen-base">SCREEN BASE</h3>
<p><i>function: get screen table</i><br>
address=<b>Screen Base</b></p>
<p>This function returns the base address of the internal table that is used to hold the number and
position of AMOS Professional screens.</p>
<h3 class="command" id="fn-icon-base">ICON BASE</h3>
<p><i>function: get Icon base</i><br>
address=<b>Icon Base</b>(number)
<p>ICON BASE returns the address of the Icon whose number is specified in brackets. The format
of this information is exactly the same as for the SPRITE BASE function, explained below.</p>
<h3 class="command" id="fn-sprite-base">SPRITE BASE</h3>
<p><i>function: get Sprite table</i><br>
n=<b>Sprite Base</b>(number)</p>
<p>
SPRITE BASE provides the address of the internal data list for whichever Sprite number is
specified in brackets. If the Sprite does not exist, then the address of the table is returned as zero.
Negative values for the Sprite number will return the address of the optional mask associated
with that Sprite, and the number that is returned can contain one of three possible values, as
follows:</p>
<ul>
<li>A <b>negative</b> number indicates that there is no mask for this Sprite.</li>
<li><b>Zero</b> indicates that the specified Sprite does have a mask, but it is yet to be generated by the
system.
</li>
<li>A <b>positive</b> number indicates the address of the mask in memory. The first "long word" of this
area holds the length of the mask, and the next gives the actual definition.
</li>
</ul>
</section>
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