Hi
I am using MSP430 F5635 .
How do i know the CPU clock frequency ?
By intention is to create a delay for some ms .
So to use the __delay_cycles function , i want to know the CPU clock frequency .
Thanks in advance
Jenitta
If instead of _delay_cycles , if i have to use _nop() for creating some delay ,
what is the time taken to execute one _nop() instruction ??
Please reply .
Thanks in advance.
Hi Jenitta,
the clock frequency is given by your configuration and your crystals used on your board.__delay_cycles(n) is a function that inserts code that needs n cycles of MCLK to run. So if your clock runs at 8MHz a cycles takes 125ns, 1ms delay then need 8000 cycles of delay.
Apart from that, if you need accurate delays you should better use a timer - they are made for this :-)
--Regards,JanOxfam Trailwalker 2012 - Runner
Found any horribly english mistakes? - Drop me a note as private conversation via my profile if you like ;-)
Hi again,
the _nop() is a special assembler instruction which does No OPeration and will take one MCLK cycle. But be aware that
volatile int i;for (i=0; i<8000; i++) { __nop();}
and __delay_cycles(8000);
will have *very* different delay times.
An easy way to check the MSP430 clocks is just to set the GPIOs to output the corresponding clock. I.e.:
- P3.4 can output SMCLK if P3SEL.4 =1 and P3DIR.4 = 1 (depending on your configuration SMCLK could be the same as MCLK)
- P1.0 can output ACLK if P1SEL.0 =1 and P1DIR.0 =1
- Any of the PortMap pins (P2[0:7]) can be configured to output MCLK. According to table 12 in the datasheet, the mnemonic is "PM_MCLK" and you can use the PMAP examples found in the code examples as a guide: http://www.ti.com/litv/zip/slac417d
Regards,
Luis R
By default the main clock MCLK is sourced from the DCO and is trimmed by the FLL to ~1MHz using REFO as reference.
See the UCS examples for how to adjust the clocks to your needs.
Also as Jan alluded to, you should use __delay_cycles if you want a cycle accurate delay function.
Tony
Thank you very much !