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Syntax

CONFIG XRAM = mode [ , WaitstateLS=wls , WaitStateHS=whs ]

Remarks

Mode	The memory mode. This is either enabled or disabled. By default, external
	memory access is disabled.
Wls	When external memory access is enabled, some chips allow you to set a
	wait state. The number of modes depend on the chip. A modern chip such
	as the Mega8515 has 4 modes :
	0	- no wait states
	1	- 1 cycle wait state during read/write
	2	- 2 cycle wait state during read/write
	3	- 2 cycle wait state during read/write and 1 before new address output
	WLS works on the lower sector. Provided that the chip supports this.
Whs	When external memory access is enabled, some chips allow you to set a
	wait state. The number of modes depend on the chip. A modern chip such
	as the Mega8515 has 4 modes :
	0	- no wait states
	1	- 1 cycle wait state during read/write
	2	- 2 cycle wait state during read/write
	3	- 2 cycle wait state during read/write and 1 before new address output
	WHS works on the high sector. Provided that the chip supports this.

Wait states are needed in case you connect equipment to the bus, that is relatively slow. Especial older electronics/chips.

Some AVR chips also allow you to divide the memory map into sections. By default the total XRAM memory address is selected when you set a wait state.

The $XA directive should not be used anymore. It is the same as CONFIG XRAM=Enabled

CONST

Action

Declares a symbolic constant.

Syntax

page -403-

CONST symbol = numconst

CONST symbol = stringconst

CONST symbol = expression

Remarks

Symbol	The name of the symbol.
Numconst	The numeric value to assign to the symbol.
Stringconst	The string to assign to the symbol
Expression	An expression that returns a value to assign the constant

Assigned constants consume no program memory because they only serve as a reference to the compiler.

The compiler will replace all occurrences of the symbol with the assigned value.

You can use a constant to give a value a more meaningful name.

For example : variable = 1

const optHeaterOn = 1 variable = optHeaterOn

The source code is better to read when you assign a constant. Even better when the values change later, for example when HeaterOn becomes 2, you only need to replace 1 line of code.

See also

ALIAS

Example

'-----------------------------------------------------------------------------
------------	: const.bas
'name	: const.bas
'copyright	: (c) 1995-2005, MCS Electronics
'purpose	: demo for constants
'micro	: Mega48
'suited for demo	: yes
'commercial addon needed	: no

'-----------------------------------------------------------------------------

------------

$regfile = "m48def.dat"	' specify the used
micro	' used crystal
$crystal = 4000000	' used crystal
frequency	' use baud rate
$baud = 19200	' use baud rate
$hwstack = 32	' default use 32
for the hardware stack	' default use 10
$swstack = 10	' default use 10
for the SW stack	' default use 40
$framesize = 40	' default use 40
for the frame space

'dimension some variables

Dim Z As String * 10 Dim B As Byte

'assign some constants

'constants dont use program memory

page -404-

	© MCS Electronics, 1995-2007
Const S = "test"		'declare a as a
Const A = 5
constant
Const	B1 = &B1001
'or use an expression to assign a constant
Const X =(b1 * 3) + 2
Const Ssingle = Sin(1)
Print X
Print Ssingle
B = A
'the same as b = 5
Z = S
'the same as Z = "test"
Print A
Print B1
Print S
'you can use constants with conditional compilation		' note there is no
#if A = 5
then
Print "constant a is 5"
#if S = "test"
Print "nested example"		' else is optional
#else
#endif
#else
#endif