Admin at 13:13, 4 February 2014

2014-02-04T13:13:51Z

Admin: Created page with "= Action
= Instruct the compiler to override the crystal frequency options setting. &n..."

2013-01-31T20:06:46Z

Created page with "= Action = Instruct the compiler to override the crystal frequency options setting. &n..."

New page

= Action =

Instruct the compiler to override the crystal frequency options setting.

 

 

= Syntax =

$CRYSTAL = var

 

 

= Remarks =
<div style="text-align: left; text-indent: 0px; padding: 0px 0px 0px 0px; margin: 0px 0px 0px 4px">
{| style="border: solid 2px #000000; border-spacing:0px; border-collapse: collapse" border="1" cellpadding="1" cellspacing="0" width="604"
|- style="text-align:left; vertical-align:top"
| style="width:13%; border: solid 1px #000000" valign="top" width="13%" |
var

| style="width:100%; border: solid 1px #000000" valign="top" width="100%" |
A numeric constant with the Frequency of the crystal.

|}
</div>
 

The frequency is selectable from the [[Options Compiler Communication]]. It is stored in a configuration file. The $CRYSTAL directive overrides this setting.

It is best to use the $CRYSTAL directive as the used crystal frequency is visible in your program that way.

 

[[File:Notice.jpg|left|Notice.jpg]] The $CRYSTAL directive only informs the compiler about the used frequency. It does not set any fuse bit. The frequency must be know by the compiler for a number of reasons. First when you use serial communications, and you specify [[$BAUD]], the compiler can calculate the proper settings for the UBR register. And second there are a number of routines like [[WAITMS]], that use the execution time of a loop to generate a delay. When you specify $CRYSTAL = 1000000 (1 MHz) but in reality, connect a 4 MHz XTAL, you will see that everything will work 4 times as quick.

 

Most new AVR chips have an internal oscillator that is enabled by default. Check the data sheet for the default value.

 

 

= See also =

[[$BAUD]] , [[BAUD]] , [[CONFIG CLOCKDIV|CONFIG CLOCKDIV]]

 

 

= Example =

<source lang="bascomavr">
$regfile = "m48def.dat"
$crystal = 4000000
$baud = 19200

Config Com1 = Dummy , Synchrone = 0 , Parity = None , Stopbits = 1 , Databits = 8 , Clockpol = 0

Print "Hello world"
End
</source> {{Languages}}

[[Category:BASCOM_Language_Reference]]

@@ Line 16: / Line 16: @@
 = <span class="f_Header">Remarks</span><br/> =
-<div style="text-align: left;  text-indent: 0px;  padding: 0px 0px 0px 0px;  margin: 0px 0px 0px 4px">
+<div style="text-align: left; text-indent: 0px; padding: 0px 0px 0px 0px; margin: 0px 0px 0px 4px">
-{| style="border: solid 2px #000000;  border-spacing:0px;  border-collapse: collapse" border="1" cellpadding="1" cellspacing="0" width="604"
+{| style="border: solid 2px #000000; border-spacing:0px; border-collapse: collapse" border="1" cellpadding="1" cellspacing="0" width="604"
-|- style="text-align:left;  vertical-align:top"
+|- style="text-align:left; vertical-align:top"
-| style="width:13%;  border: solid 1px #000000" valign="top" width="13%" |
+| style="width:13%; border: solid 1px #000000" valign="top" width="13%" |
 var
-| style="width:100%;  border: solid 1px #000000" valign="top" width="100%" |
+| style="width:100%; border: solid 1px #000000" valign="top" width="100%" |
 A numeric constant with the Frequency of the crystal.
 |}
 </div>
-<span style="font-family: 'Arial';  color: #000000">&nbsp;</span>
+<span style="font-family: 'Arial'; color: #000000">&nbsp;</span>
 The frequency is selectable from the [[Options Compiler Communication]]. It is stored in a configuration file. The $CRYSTAL directive overrides this setting.
@@ Line 33: / Line 33: @@
 It is best to use the $CRYSTAL directive as the used crystal frequency is visible in your program that way.
-<span style="font-family: 'Arial';  color: #000000">&nbsp;</span>
+<span style="font-family: 'Arial'; color: #000000">&nbsp;</span>
 [[File:Notice.jpg|left|Notice.jpg]]&nbsp;The $CRYSTAL directive only informs the compiler about the used frequency. It does not set any fuse bit. The frequency must be know by the compiler for a number of reasons. First when you use serial communications, and you specify [[$BAUD]], the compiler can calculate the proper settings for the UBR register. And second there are a number of routines like [[WAITMS]], that use the execution time of a loop to generate a delay. When you specify $CRYSTAL = 1000000 (1 MHz) but in reality, connect a 4 MHz XTAL, you will see that everything will work 4 times as quick.
-<span style="font-family: 'Arial';  color: #000000">&nbsp;</span>
+<span style="font-family: 'Arial'; color: #000000">&nbsp;</span>
-Most new AVR chips have an internal oscillator that is enabled by default. Check the data sheet for the default value.
+[[File:Notice.jpg]]Most new AVR chips have an internal oscillator that is enabled by default. Check the data sheet for the default value.
-<span style="font-family: 'Arial';  color: #000000">&nbsp;</span>
+Most new AVR chips have an option to divide the oscillator frequency by a number of values. If these options are used you need to take this into account.
-<span style="font-family: 'Arial';  color: #000000">&nbsp;</span>
+For example, you connect a 16 MHz crystal and select the external oscillator fuse byte, this would result in a 16 MHz clock for most old processors.
 = <span class="f_Header">See also</span><br/> =

$CRYSTAL - Revision history

Admin at 13:13, 4 February 2014

Admin: Created page with "= Action = Instruct the compiler to override the crystal frequency options setting. &n..."

Admin: Created page with "= Action
= Instruct the compiler to override the crystal frequency options setting. &n..."