lpcware

LPCXpresso LPC11C24 clock generation

Discussion created by lpcware Employee on Jun 16, 2016
Latest reply on Jun 16, 2016 by lpcware

Content originally posted in LPCWare by dlchnr on Tue Jul 26 02:29:21 MST 2011
Hello,
I'm working with a LPC11C24 LPCXpresso board and try to understand
the "can_onchip" example.
Now I've a problem to understand the clock generation.
The used CAN_BTR value (0x00001C57UL) and a measurement at
PIO0_1 (CLKOUT) tell me, the LPC11C24 will run with 48MHz.
"SYSPLLCTRL_Val" is defined as 0x00000023 in "system_LPC11xx.h".
The "3" will lead to a MSEL value of 4, which fits to the oscillator input
of 12MHz placed on the board according to the schematic (48MHz / 4 = 12MHz).
But the PSEL value of "2" will result in a post divider ratio P of  4 with a
division ratio of  8 ("division ratio is 2 x P"), which leads to a FCCO
(Frequency of the Current Controlled Oscillator) of 384MHz.
That's out of the 156 to 320 MHz range required!?
Where is error in my chain of thought?
Thx, dlchnr

 

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