topic Re: LPC844 clock out in LPC Microcontrollers

LPC844 clock out

tyassin1 — Sun, 07 Mar 2021 08:04:34 GMT

I m trying a very simple example, to get the CLKOUT to work on a LPC844.

I am using the below SDK

I make a project and use the code below to output the MAINCLK to PIO0_24:

SWM0->PINASSIGN_DATA[11] &= ~(0xFF<<8);
SWM0->PINASSIGN_DATA[11] |= (24<<8);
SYSCON->CLKOUTSEL = 1;
SYSCON->CLKOUTDIV = 1;

But nothing happens on the pin. I am missing something?

Thomas

Re: LPC844 clock out

xiangjun_rong — Mon, 08 Mar 2021 01:03:05 GMT

Hi, Thomas,

How about using the code like:

SYSCON->SYSAHBCLKCTRL0|=1<<7; //or //SYSCON->SYSAHBCLKCTRL[0]|=1<<7;

SWM0->PINASSIGN_DATA[11] &= ~(0xFF<<8);
SWM0->PINASSIGN_DATA[11] |= (24<<8);
SYSCON->CLKOUTSEL = 1;
SYSCON->CLKOUTDIV = 100; //decrease the output clcok frqeuency for test

Hope it can help you

XiangJun Rong

Re: LPC844 clock out

tyassin1 — Mon, 08 Mar 2021 16:38:44 GMT

Hi,

Thank you for feedback.

First of all.....it works now

The missing part was the activation of the SWM: SYSCON->SYSAHBCLKCTRL0|=1<<7;

But I had thought about it and looking in the manual:

It states that it is enabled from reboot or am I missing something?

Thomas

Re: LPC844 clock out

xiangjun_rong — Tue, 09 Mar 2021 02:32:37 GMT

Hi, Thomas,

It is good new that it works well. Regarding the SWM bit which is set in default after reset based on the Table 147. System clock control 0 register, maybe it is documentation error, the bit SWM is cleared in default after reset.

XiangJun Rong

Re: LPC844 clock out

tyassin1 — Tue, 09 Mar 2021 12:03:15 GMT

Maybe there is no error after all.

When I look in the user manual, then I don't think table 147 is the right table you refer too. I refer to table 146 (SYSAHBCLKCTRL0).

But continuing to table 148 (PRESETCTRL0) (maybe also the one you meant instead of table 147), then I can see that SWM is reset by default, but this can be changed in this register.

So I guess that SYSAHBCLKCTRL0 can be changed on the fly in the code and PRESETCTRL0 is a startup thing when it boots.

Thomas