Post by thread:[PIC]:How can i calculate instruction delay

i.e How can i calculate the nop delay if working with a 4MHz crystal. I've seen many examples that calculate this delay in various ways but the result is not the same. Thanks in advance, for any help George Chatzigeorgiou -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

The PIC I have a little experience with (16f877) has a 4 clock instruction cycle. I _think_ this is true of all pics. The databook for this chip says that a NOP takes one instruction cycle. so the time for one NOP is: (1*4/4000000) = 1uS One thing worth bearing in mind though when you are doing delay loops for sampling data at specific times is that 'movf port, W' will sample the data on the port towards the start of the instruction cycle, and 'movwf port' will output data towards the end. I think the details for these timings are in the datasheet (i.e. which clock of an instruction cycle things happen on). Regards, Simon Please respond to pic microcontroller discussion list <spam_OUTPICLISTTakeThisOuTMITVMA.MIT.EDU> To: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU cc: (bcc: Simon Nield/Quantel Research) Subject: [PIC]:How can i calculate instruction delay i.e How can i calculate the nop delay if working with a 4MHz crystal. I've seen many examples that calculate this delay in various ways but the result is not the same. Thanks in advance, for any help George Chatzigeorgiou -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

>The PIC I have a little experience with (16f877) has a 4 clock instruction cycle. I _think_ this is >true of all pics. Except 18C parts, which can have 1:1 if you turn on the PLL. Andy -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> Except 18C parts, which can have 1:1 if you turn on the PLL. Well, sorta. In reality of course, the PIC is still running internally at 4x the instruction rate. But it sure is nice to get a 40Mhz CPU clock with only a 10MHz XTAL. btw: has anybody had any experience with overclocking 18C's? I accidently overclocked one at 11.056 MHz (ie 44+MHz internally) when Digikey sent me the wrong crystal. It worked fine at room temp. Bob Ammerman RAm Systems (contract development of high performance, high function, low-level sofftware) -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> i.e How can i calculate the nop delay if working with a 4MHz crystal. > I've seen many examples that calculate this delay in various ways but the > result is not the same. It takes 4 clock cycles to execute each simple instruction like a NOP. With a 4MHz clock you can run instructions at a 1MHz rate, which means the delay for an individual NOP is 1uS. ***************************************************************** Olin Lathrop, embedded systems consultant in Devens Massachusetts (978) 772-3129, olinKILLspamcognivis.com, http://www.cognivis.com -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

George, Did you know that there is a delay code generator at http://www.piclist.com/codegen It generates a delay routine with one instruction cycle resolution using nested loops. Just enter needed time or cycles in the form and hit the generate button! Hope it helps. Nikolai ---- Original Message ---- From: George Chatzigeorgiou Sent: Tuesday, August 15, 2000 16:49:49 To: .....PICLISTKILLspam.....MITVMA.MIT.EDU Subj: [PIC]:How can i calculate instruction delay {Quote hidden}> i.e How can i calculate the nop delay if working with a 4MHz crystal. > I've seen many examples that calculate this delay in various ways but the > result is not the same. > Thanks in advance, for any help > George Chatzigeorgiou > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.