Clock setup for Tiva C LaunchPad TM4C123GXL?

khanhoct

I begin with Tiva C LaunchPad TM4C123GXL and Keil C ver 5. I'm following tutorial in TM4C123G workbook.

Lab 3: Initialization and GPIO. I met one the following code:

SysCtlClockSet(SYSCTL_SYSDIV_5|SYSCTL_USE_PLL|SYSCTL_XTAL_16MHZ|SYSCTL_OSC_MAIN);

And I don't understand what SYSCTL_XTAL_16MHZ mean?

over 9 years ago

0 Chuck Davenport over 9 years ago

TI__Guru 59540 points

Hello khanhoct,

This is simply the #define meaning a 16MHz external crystal is being used. More information on this API and the acceptable parameters to be used can be found in the TivaWare™ Peripheral Driver Library for C Series User's Guide (Rev. A) located at this link: www.ti.com/.../spmu298

0 khanhoct over 9 years ago in reply to Chuck Davenport

Prodigy 20 points

T think external crystal of Kit always is 16MHz?

And TivaWare™ Peripheral Driver Library show that, we can choose with one of the following value: SYSCTL_XTAL_4MHZ, SYSCTL_XTAL_4_09MHZ, SYSCTL_XTAL_4_91MHZ... So when we can change them?

0 Chuck Davenport over 9 years ago in reply to khanhoct

TI__Guru 59540 points

Hello khanhoct,

These defines are there to accommodate custom designs and potential crystal values that were considered at the time of the chip development. If you only use the Launchpad, you would not need to change the value unless you replaced the included crystal with a different value.

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Clock setup for Tiva C LaunchPad TM4C123GXL?