LPC1768 PLL1 Lock USB

lpcware — Thu, 16 Jun 2016 01:02:43 GMT

Content originally posted in LPCWare by kiryat8 on Thu Apr 19 03:23:12 MST 2012
I am using a LPC1768 board (12MHz crystal) with Code Red CMSISv2.
This is a low power project so I must turn off both PLLs most of the time.
My problem is that I do need the USB serial interface for parameter update after manual user input.
If I enable both defines PLL0_SETUP & PLL1_SETUP in the CMSIS lib file,
my USB serial code (from example) works fine but I consume too much current.

If I enabled only PLL1_SETUP with PLL1CFG_Val the default 0x23 value but the USB does not work.

I had thought to switch on PLL1 when I need USB and then switch it back off.
When both defines are zero and I then try to enable only PLL1, PLL1 does not lock after the first enable and loops forever. The LPC1768 is running from the Crystal at this stage.

I can not see any problem in my code.
//---------------------------------------------------------------------------
// Switch power to main crystal oscillator on
//---------------------------------------------------------------------------
LPC_SC->SCS = OSCEN;
while ((LPC_SC->SCS & OSCSTAT) == 0);
LPC_SC->PLL1CFG   = PLL1CFG_Val;           // 0x23
LPC_SC->PLL1FEED = PLLFEED1;              // 0xAA
LPC_SC->PLL1FEED = PLLFEED2;              // 0x55
//---------------------------------------------------------------------------
// PLL1 Enable
//---------------------------------------------------------------------------
LPC_SC->PLL1CON   = CLKPWR_PLL1CON_ENABLE; // 0x01
LPC_SC->PLL1FEED = PLLFEED1;              // 0xAA
LPC_SC->PLL1FEED = PLLFEED2;              // 0x55
//---------------------------------------------------------------------------
// Wait for LOCK
//---------------------------------------------------------------------------
while (!(LPC_SC->PLL1STAT & CLKPWR_PLL1STAT_PLOCK)); // (1<<10)
//---------------------------------------------------------------------------
// PLL1 Enable & Connect
//---------------------------------------------------------------------------
LPC_SC->PLL1CON   = CLKPWR_PLL1CON_ENABLE | CLKPWR_PLL1CON_CONNECT; // 0x01 | 0x02
LPC_SC->PLL1FEED = PLLFEED1;             // 0xAA
LPC_SC->PLL1FEED = PLLFEED2;             // 0x55
//---------------------------------------------------------------------------
// Wait for PLLC1_STAT & PLLE1_STAT
//---------------------------------------------------------------------------
while (!(LPC_SC->PLL1STAT & (CLKPWR_PLL1STAT_PLLE | CLKPWR_PLL1STAT_PLLC)));

Any help would be appreciated.

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LPC1768 PLL1 Lock USB