TMS320F28027: About external clock input

Keirs,

Thanks for reaching out, I want to make sure you are following the guidelines/using the C2000 Ware examples to switch from internal oscillator to external clock.

First all the F2802x examples call the file F2802x.sysctrl.c.  This file is located in:

C:\ti\c2000\C2000Ware_1_00_04_00\device_support\f2802x\common\source

While the default is to use the built in zero pin oscillator 1; you will find function calls for zero pin oscillator 2, external X-tal, and external clock(which is what you want to follow):  The order of operations is important here, else you will get a clock fail even if there is a good clock on the XCLKIN pin.

void
ExtOscSel (void)
{
    EALLOW;
    
    //
    // 1-GPIO19 = XCLKIN, 0-GPIO38 = XCLKIN
    //
    SysCtrlRegs.XCLK.bit.XCLKINSEL = 1;
    
    SysCtrlRegs.CLKCTL.bit.XTALOSCOFF = 1;    // Turn on XTALOSC
    SysCtrlRegs.CLKCTL.bit.XCLKINOFF = 0;     // Turn on XCLKIN
    SysCtrlRegs.CLKCTL.bit.OSCCLKSRC2SEL = 0; // Switch to external clock
    
    //
    // Switch from INTOSC1 to INTOSC2/ext clk
    //
    SysCtrlRegs.CLKCTL.bit.OSCCLKSRCSEL = 1;
    
    //
    // Switch Watchdog Clk Src to internal clock 1
    //
    SysCtrlRegs.CLKCTL.bit.WDCLKSRCSEL = 0;
    
    SysCtrlRegs.CLKCTL.bit.INTOSC2OFF = 1;    // Turn off INTOSC2
    SysCtrlRegs.CLKCTL.bit.INTOSC1OFF = 0;    // Turn on INTOSC1
    EDIS;
}

//
// End of file
//

The clock options/mux pins are detailed on page 35 of this doc  http://www.ti.com/lit/ug/sprufn3d/sprufn3d.pdf

If you have followed all of these, then you need to confirm the levels of the clock input and rise times meet the DS specs.

Let me know if this solves it, or there is something else not working.

Best,

Matthew