DIM - Revision history

Admin at 18:53, 15 June 2015

2015-06-15T18:53:50Z

Show changes

Admin at 18:52, 15 June 2015

2015-06-15T18:52:32Z

Admin at 18:51, 15 June 2015

2015-06-15T18:51:02Z

Admin at 21:11, 13 December 2014

2014-12-13T21:11:15Z

Admin at 17:50, 8 February 2013

2013-02-08T17:50:46Z

Admin at 17:50, 8 February 2013

2013-02-08T17:50:07Z

Show changes

Admin at 17:49, 8 February 2013

2013-02-08T17:49:05Z

Admin: Created page with "= Action = Dimension a variable. =
2013-02-08T17:48:06Z

Created page with "= Action = Dimension a variable. = Action =

Dimension a variable.

 

 

= Syntax =

DIM var AS [XRAM/SRAM/ERAM]type [AT location/variable] [OVERLAY]

 

 

Remarks
<div style="padding: 0px; margin: 0px 0px 0px 4px;">
{| width="547" cellspacing="0" cellpadding="1" border="1" style="border: 2px solid rgb(0, 0, 0); border-spacing: 0px; border-collapse: collapse;"
|- style="vertical-align: top;"
| valign="top" width="18%" style="width: 95px; height: 48px; border: 1px solid rgb(0, 0, 0);" |
Var

| valign="top" width="85%" style="width: 443px; height: 48px; border: 1px solid rgb(0, 0, 0);" |
Any valid variable name such as b1, i or longname. var can also be an array : ar(10) for example.

 

|- style="vertical-align: top;"
| valign="top" width="18%" style="width: 95px; border: 1px solid rgb(0, 0, 0);" |
Type

| valign="top" width="85%" style="width: 443px; border: 1px solid rgb(0, 0, 0);" |
Bit, Byte, Word, Integer, Long, Dword, Single, Double or String

|- style="vertical-align: top;"
| valign="top" width="18%" style="width: 95px; border: 1px solid rgb(0, 0, 0);" |
XRAM

| valign="top" width="85%" style="width: 443px; border: 1px solid rgb(0, 0, 0);" |
Specify XRAM to store variable into external memory

|- style="vertical-align: top;"
| valign="top" width="18%" style="width: 95px; border: 1px solid rgb(0, 0, 0);" |
SRAM

| valign="top" width="85%" style="width: 443px; border: 1px solid rgb(0, 0, 0);" |
Specify SRAM to store variable into internal memory (default)

|- style="vertical-align: top;"
| valign="top" width="18%" style="width: 95px; height: 16px; border: 1px solid rgb(0, 0, 0);" |
ERAM

| valign="top" width="85%" style="width: 443px; height: 16px; border: 1px solid rgb(0, 0, 0);" |
Specify ERAM to store the variable into EEPROM

|- style="vertical-align: top;"
| valign="top" width="18%" style="width: 95px; border: 1px solid rgb(0, 0, 0);" |
OVERLAY

| valign="top" width="85%" style="width: 443px; border: 1px solid rgb(0, 0, 0);" |
Specify that the variable is overlaid in memory.

|- style="vertical-align: top;"
| valign="top" width="18%" style="width: 95px; border: 1px solid rgb(0, 0, 0);" |
location

| valign="top" width="85%" style="width: 443px; border: 1px solid rgb(0, 0, 0);" |
The address of name of the variable when OVERLAY is used.

|}
</div>
 

 

A string variable needs an additional length parameter:

Dim s As XRAM String * 10

 

In this case, the string can have a maximum length of 10 characters. Internally one additional byte is needed to store the end of string marker. Thus in the example above, 11 bytes will be used to store the string.

 

Note that BITS can only be stored in internal memory.

 

You may also specify IRAM. IRAM is the place in memory where the registers are located : absolute address 0 - 31. BASCOM uses most of these addresses, depending on the instructions/options you use. For a [[$TINY]] chip it makes sense to use IRAM since there is NO SRAM in most tiny AVR chips (TINY15 for example). You may also use to IRAM to overlay registers in memory.

 

See also [[Memory_usage|Memory usage]]

 

= SCOPE =

The scope for DIM is global. So no matter where you use the DIM statements, the variable will end up as a global visible variable that is visible in all modules, procedures and functions.

When you need a LOCAL variable that is local to the procedure or function, you can use [[LOCAL]].

Since LOCAL variables are stored on the frame, it takes more code to dynamic generate and clean up these variables.

 

 

= AT =

The optional AT parameter lets you specify where in memory the variable must be stored. When the memory location already is occupied, the first free memory location will be used. You need to look in the report file to see where the variable is located in memory.

 

 

= OVERLAY =

The OVERLAY option will not use any variable space. It will create a sort of phantom variable.

 

Dim x as Long at $60 'long uses 60,61,62 and 63 hex of SRAM   Dim B1 As Byte At $60 Overlay                     '$60 is the same as &H60 Dim B2 As Byte At $61 Overlay  

B1 and B2 are no real variables! They refer to a place in memory. In this case to &H60 and &H61. By assigning the phantom variable B1, you will write to memory location &H60 that is used by variable X.

So to define it better, OVERLAY does create a normal usable variable, but it will be stored at the specified memory location which could be already be occupied by another OVERLAY variable, or by a normal variable.

 

[[File:Notice.jpg|left]]Take care with the OVERLAY option. Use it only when you understand it.

 

 

You can also read the content of B1:

Print B1

 

This will print the content of memory location &H60.

 

By using a phantom variable you can manipulate the individual bytes of real variables.

 

 

= Overlay example 2 =

Dim L as Long at &H60 Dim W as Word at &H62 OVERLAY

 

W will now point to the upper two bytes of the long.

 

= Overlay example 3 =

 

Following you find the Bascom-AVR Simulator Memory status when you run the following example in Bascom-AVR Simulator. This example is intended to be used with the simulator. You need to uncomment the $sim when you want to test it on an real AVR.

 

[[File:Notice.jpg|left]]Strings need an additional byte (Null termination). So you need an overlay of 8 bytes when you overlay a string with 7 bytes.

[[File:Overlay example 1.jpg|center]]

= Using variable name instead of address =

As variables can be moved though the program during development it is not always convenient to specify an address. You can also use the name of the variable :

 

DIM W as WORD

Dim B as BYTE AT W OVERLAY

 

Now B is located at the same address as variable W.

 

For XRAM variables, you need [[Adding_XRAM_with_External_Memory_Interface|additional hardware ]]: an external RAM and address decoder chip.

 

 

= ERAM =

For ERAM variables, it is important to understand that these are not normal variables. ERAM variables serve as a way to simple read and write the EEPROM memory. You can use READEEPROM and WRITEEEPROM for that purpose too.

 

To write to an ERAM variable you have to use an SRAM variable as the source : eramVAR= sramVAR

To read from an ERAM variable you have to use an SRAM variable as the targer : sramVAR=eramVAR

Both variables need to be of the same data type. So when writing to an ERAM double, the source variable need to be of the double type too.

ERAM can be assigned with a numeric value too : eramVAR= 123

 

You can not use an ERAM variable as you would use a normal variable.

 

Also keep in mind that when you write to ERAM, you write to EEPROM, and that after 100.000 times, the EEPROM will not erase properly.

 

Dim b as byte, bx as ERAM byte

B= 1

Bx=b ' write to EEPROM

B=bx ' read from EEPROM

 

 

= Xmega =

The XMEGA need an additional configuration command : [[CONFIG_EEPROM|CONFIG EEPROM]] = MAPPED, in order to use ERAM.

 

 

= Size =

The maximum size of an array depends on the available memory and the data type. The XMEGA supports up to 8 MB of external memory. BASCOM supports this but the implementation is still considered BETA. It should not be used for production. The only thing you need to do to activate the big memory is to specify the size with $XRAMSIZE.

For example : $XRAMSIZE=8000000 will tell the compiler that you use 8 MB of external memory.

Additional registers must be set to pass the 24 bit address. This will create more code.

There is only one restriction : you can/may not pass variables located in the external memory to a sub or function.

The compiler will always pass a word address and does not support to pass the additional byte.

 

 

 

= See Also =

[http://avrhelp.mcselec.com/const.htm CONST] , [http://avrhelp.mcselec.com/local.htm LOCAL], [http://avrhelp.mcselec.com/memory_usage.htm Memory usage]

 

 

= Example =

@@ Zeile 19: / Zeile 19: @@
 {| cellspacing="0" cellpadding="1" border="1" style="border: 2px solid rgb(0, 0, 0); border-spacing: 0px; border-collapse: collapse;"
 |- style="vertical-align: top;"
-| valign="top" width="18%" style="width: 149px; height: 48px; border: 1px solid rgb(0, 0, 0);" |
+| valign="top" width="18%" style="width: 176px; height: 48px; border: 1px solid rgb(0, 0, 0);" |
 Var
-| valign="top" width="143%" style="width: 689px; height: 48px; border: 1px solid rgb(0, 0, 0);" |
+| valign="top" width="143%" style="width: 811px; height: 48px; border: 1px solid rgb(0, 0, 0);" |
-Any valid variable name such as b1, i or longname. var may also be an array : ar(10) for example.
+Any valid variable name such as b1, i or longname. var may also be an array&nbsp;: ar(10) for example.
-You can also use a list and created a number of variables of the same data type : &nbsp;DIM A1,A2, BVAR AS BYTE. This will create 3 BYTE variables. When using a list, you may not use identifiers such as #%!&. You may also not use the optional OVERLAY.
+You can also use a list and created a number of variables of the same data type&nbsp;: &nbsp;DIM A1,A2, BVAR AS BYTE. This will create 3 BYTE variables. When using a list, you may not use identifiers such as #%!&. You may also not use the optional OVERLAY.
-It is also possible to define the data type by ending the variable name with an identifier :
+<span style="font-size: 10pt;">&nbsp;</span>
-% for Integer
+We encourage the use of Hungarian Notation where you use a prefix instead&nbsp;:
-−
-& for Long
-−
-# for Double
-−
-! for Single
-−
-Dim A!, b# &nbsp;would create a variable A! of the SINGLE data type and a variable B# with the DOUBLE data type
-−
-When a variable is dimensioned with an identifier, the variable must be referenced with that identifier as well.
-−
-&nbsp;
-−
 We encourage the use of Hungarian Notation where you use a prefix instead :
 Dim bVar As Byte ' the b indicates a BYTE
@@ Zeile 49: / Zeile 35: @@
 Dim iMyInt As Integer 'the i indicates an INTEGER
-common used prefixes :
+common used prefixes&nbsp;:
 b - BYTE
@@ Zeile 72: / Zeile 58: @@
 |- style="vertical-align: top;"
-| valign="top" width="18%" style="width: 149px; border: 1px solid rgb(0, 0, 0);" |
+| valign="top" width="18%" style="width: 176px; border: 1px solid rgb(0, 0, 0);" |
 Type
-| valign="top" width="143%" style="width: 689px; border: 1px solid rgb(0, 0, 0);" |
+| valign="top" width="143%" style="width: 811px; border: 1px solid rgb(0, 0, 0);" |
 Bit/Boolean, Byte, Word, Integer, Long, Dword, Single, Double or String
 |- style="vertical-align: top;"
-| valign="top" width="18%" style="width: 149px; border: 1px solid rgb(0, 0, 0);" |
+| valign="top" width="18%" style="width: 176px; border: 1px solid rgb(0, 0, 0);" |
 XRAM
-| valign="top" width="143%" style="width: 689px; border: 1px solid rgb(0, 0, 0);" |
+| valign="top" width="143%" style="width: 811px; border: 1px solid rgb(0, 0, 0);" |
 Specify XRAM to store variable into external memory
 |- style="vertical-align: top;"
-| valign="top" width="18%" style="width: 149px; border: 1px solid rgb(0, 0, 0);" |
+| valign="top" width="18%" style="width: 176px; border: 1px solid rgb(0, 0, 0);" |
 SRAM
-| valign="top" width="143%" style="width: 689px; border: 1px solid rgb(0, 0, 0);" |
+| valign="top" width="143%" style="width: 811px; border: 1px solid rgb(0, 0, 0);" |
 Specify SRAM to store variable into internal memory (default)
 |- style="vertical-align: top;"
-| valign="top" width="18%" style="width: 149px; height: 16px; border: 1px solid rgb(0, 0, 0);" |
+| valign="top" width="18%" style="width: 176px; height: 16px; border: 1px solid rgb(0, 0, 0);" |
 ERAM
-| valign="top" width="143%" style="width: 689px; height: 16px; border: 1px solid rgb(0, 0, 0);" |
+| valign="top" width="143%" style="width: 811px; height: 16px; border: 1px solid rgb(0, 0, 0);" |
 Specify ERAM to store the variable into EEPROM
 |- style="vertical-align: top;"
-| valign="top" width="18%" style="width: 149px; border: 1px solid rgb(0, 0, 0);" |
+| valign="top" width="18%" style="width: 176px; border: 1px solid rgb(0, 0, 0);" |
 OVERLAY
-| valign="top" width="143%" style="width: 689px; border: 1px solid rgb(0, 0, 0);" |
+| valign="top" width="143%" style="width: 811px; border: 1px solid rgb(0, 0, 0);" |
 Specify that the variable is overlaid in memory.
 |- style="vertical-align: top;"
-| valign="top" width="18%" style="width: 149px; border: 1px solid rgb(0, 0, 0);" |
+| valign="top" width="18%" style="width: 176px; border: 1px solid rgb(0, 0, 0);" |
 location
-| valign="top" width="143%" style="width: 689px; border: 1px solid rgb(0, 0, 0);" |
+| valign="top" width="143%" style="width: 811px; border: 1px solid rgb(0, 0, 0);" |
 The address or name of the variable when OVERLAY is used.
 |}
 </div>
 A string variable needs an additional length parameter:
@@ Zeile 133: / Zeile 115: @@
 &nbsp;
-You may also specify IRAM. IRAM is the place in memory where the registers are located : absolute address 0 - 31. BASCOM uses most of these addresses, depending on the instructions/options you use. For a&nbsp;[[$TINY]]&nbsp;chip it makes sense to use IRAM since there is NO SRAM in most tiny AVR chips (TINY15 for example). You may also use to IRAM to overlay registers in memory.
+You may also specify IRAM. IRAM is the place in memory where the registers are located&nbsp;: absolute address 0 - 31. BASCOM uses most of these addresses, depending on the instructions/options you use. For a&nbsp;[[$TINY]]&nbsp;chip it makes sense to use IRAM since there is NO SRAM in most tiny AVR chips (TINY15 for example). You may also use to IRAM to overlay registers in memory.
 &nbsp;
-See also&nbsp;[[Memory_usage|Memory usage]]
+See also&nbsp;[[Memory usage|Memory usage]]
 </div>

@@ Zeile 462: / Zeile 462: @@
 The maximum size of an array depends on the available memory and the data type. The XMEGA supports up to 8 MB of external memory. BASCOM supports this but the implementation is still considered BETA. It should not be used for production. The only thing you need to do to activate the big memory is to specify the size with $XRAMSIZE.
-For example : $XRAMSIZE=8000000 will tell the compiler that you use 8 MB of external memory.
+For example&nbsp;: $XRAMSIZE=8000000 will tell the compiler that you use 8 MB of external memory.
 Additional registers must be set to pass the 24 bit address. This will create more code.
-There is only one restriction : you can/may not pass variables located in the external memory to a sub or function.
+There is only one restriction&nbsp;: you can/may not pass variables located in the external memory to a sub or function.
 The compiler will always pass a word address and does not support to pass the additional byte.
@@ Zeile 472: / Zeile 472: @@
 &nbsp;
-<span style="font-family: Arial;">&nbsp;</span>
+= <span class="f_Header">Arrays</span> =
-<span style="font-family: Arial;">&nbsp;</span>
+An array is a sequential collection of elements with the same data type. Till version 2077, arrays could have only 1 index or dimension. But in 2078 this has been changed and while there are no technical limits for unlimited indexes, the limit has been set to 5. This means that you can create a variable
 = <span class="f_Header">See Also</span> =

← Nächstältere Version		Version vom 8. Februar 2013, 17:50 Uhr
Zeile 486:		Zeile 486:
	= <span class="f_Header">Example</span> =		= <span class="f_Header">Example</span> =

		+	<br/><source lang="bascomavr">
		+	'-----------------------------------------------------------------------------------------
		+	'name : dim.bas
		+	'copyright : (c) 1995-2005, MCS Electronics
		+	'purpose : demo: DIM
		+	'micro : Mega48
		+	'suited for demo : yes
		+	'commercial addon needed : no
		+	'-----------------------------------------------------------------------------------------
		+
		+	$regfile = "m48def.dat" ' specify the used micro
		+	$crystal = 4000000 ' used crystal frequency
		+	$baud = 19200 ' use baud rate
		+	$hwstack = 32 ' default use 32 for the hardware stack
		+	$swstack = 10 ' default use 10 for the SW stack
		+	$framesize = 40 ' default use 40 for the frame space
		+
		+	Dim B1 As Bit 'bit can be 0 or 1
		+	Dim A As Byte 'byte range from 0-255
		+	Dim C As Integer 'integer range from -32767 - +32768
		+	Dim L As Long
		+	Dim W As Word
		+	Dim S As String * 11 'length can be up to 11 characters
		+
		+	'new feature : you can specify the address of the variable
		+	Dim K As Integer At &H120
		+	'the next dimensioned variable will be placed after variable s
		+	Dim Kk As Integer
		+
		+
		+	'Assign bits
		+	B1 = 1 'or
		+	Set B1 'use set
		+
		+	'Assign bytes
		+	A = 12
		+	A = A + 1
		+
		+	'Assign integer
		+	C = -12
		+	C = C + 100
		+	Print C
		+
		+	W = 50000
		+	Print W
		+
		+	'Assign long
		+	L = 12345678
		+	Print L
		+
		+	'Assign string
		+	S = "Hello world"
		+	Print S
		+	End
		+	</source><br/>{{Languages}}

−	~~ ~~	+	[[Category:BASCOM Language Reference]]

@@ Zeile 264: / Zeile 264: @@
 = <span class="f_Header">See Also</span> =
-[http://avrhelp.mcselec.com/const.htm CONST]&nbsp;,&nbsp;[http://avrhelp.mcselec.com/local.htm LOCAL],&nbsp;[http://avrhelp.mcselec.com/memory_usage.htm Memory usage]
+[[CONST]]&nbsp;,&nbsp;[[LOCAL]]&nbsp;,&nbsp;[[Memory_usage|Memory usage]]
 <span style="font-family: Arial;">&nbsp;</span>