Post by thread:[PIC]: Extending TMR2

I'm currently using a 16f876 20Mhz. in an application. I need to delay an output between 0.06s and 0.003s. I have pre and post scaled to 16 on TMR2 but can only get a max. delay of 0.029s I can not afford the overhead of waiting and counting interrupts. does anyone have any *smart* ideas to extend the time period? ******************************************************************** This email and any attachments are confidential to the intended recipient and may also be privileged. If you are not the intended recipient please delete it from your system and notify the sender. You should not copy it or use it for any purpose nor disclose or distribute its contents to any other person. ******************************************************************** -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

Mike Blakey wrote: > > I'm currently using a 16f876 20Mhz. in an application. I need to delay an output > between 0.06s and 0.003s. > > I have pre and post scaled to 16 on TMR2 but can only get a max. delay of 0.029s I > can not afford the overhead of waiting and counting interrupts. does anyone have > any *smart* ideas to extend the time period? Hi Mike, what's the main problem? Do you need seamless and adjustable period delays? What resolution do you need, how may total delay periods do you need etc. More info is needed before the best solution can be suggested. :o) -Roman -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

>I'm currently using a 16f876 20Mhz. in an application. I need to delay an >output >between 0.06s and 0.003s. > >I have pre and post scaled to 16 on TMR2 but can only get a max. delay of >0.029s I >can not afford the overhead of waiting and counting interrupts. does anyone >have >any *smart* ideas to extend the time period? Maybe this isn't what you're looking for, since you haven't included any details about the function of your program, but, how about this: 1) Clear a flag bit when you set your output low (for example) 2) When you get your .029s interrupt, check the flag bit. If clear, set it. If set, then change your output high (2*.029s ~ .06s). Of course, you'd have to set your delay for 1/2 of what you need, then use the flag to double it. I'm not sure if you need better precision, but since you mentioned a range of .003s and .06s, this might be good enough. And you'd only have a .002s max error (assuming your max. delay possible is REALLY .0290 seconds) with the flag's doubling effect. --Andrew _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Thanks for the help. I need to vary a pulse width between 0.06s and 0.003s (using a 20Mhz, TMR2 16prescale & 16 post scale, that is a count of between 563 and 4) obviously, I run out at a count of 255 (0.029s) whilst TMR2 is timing this period the PIC is busy doing other stuff. What am after is to put a value into TMR2, set the output, have it time out the required period, interrupt once to reset the output, therefore giving me the simple variable pulse width. This is a repetitive pulse, but is initiated from an other input. All the other timers are 'in-use'. 8bit resolution is fine, and a minimum resolution of approx. 0.00012 will be fine. Thanks for any advice. .....fastvidKILLspam.....EZY.NET.AU on 18/10/2001 01:25:43 Please respond to EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDUspam_OUTTakeThisOuTINTERNETspam_OUTTakeThisOuTwtgw To: PICLISTspam_OUTMITVMA.MIT.EDUspam_OUTINTERNETspam_OUTwtgw cc: Paper Mail: Subject: Re: [PIC]: Extending TMR2 *** WARNING *** This mail has originated outside your organization, either from an external partner or the Global Internet. Keep this in mind if you answer this message. Mike Blakey wrote: > > I'm currently using a 16f876 20Mhz. in an application. I need to delay an output > between 0.06s and 0.003s. > > I have pre and post scaled to 16 on TMR2 but can only get a max. delay of 0.029s I > can not afford the overhead of waiting and counting interrupts. does anyone have > any *smart* ideas to extend the time period? Hi Mike, what's the main problem? Do you need seamless and adjustable period delays? What resolution do you need, how may total delay periods do you need etc. More info is needed before the best solution can be suggested. :o) -Roman -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body ******************************************************************** This email and any attachments are confidential to the intended recipient and may also be privileged. If you are not the intended recipient please delete it from your system and notify the sender. You should not copy it or use it for any purpose nor disclose or distribute its contents to any other person. ******************************************************************** -- http://www.piclist.com hint: To leave the PICList KILLspampiclist-unsubscribe-requestKILLspammitvma.mit.edu

Thanks for the reply, This is exactly what I was looking for, the only problem I have is that during the pulse period the PIC is 'busy' doing some other stuff! I think I'm going to have to do as you have suggested, even counting several interrupts will give higher resolution, but may cause me stack problems, which is what I am trying to avoid. Thanks for the help. RemoveMEsnurpleTakeThisOuTHOTMAIL.COM on 17/10/2001 15:10:56 Please respond to spamBeGonePICLISTspamBeGoneMITVMA.MIT.EDUspamBeGoneINTERNETspamBeGonewtgw To: TakeThisOuTPICLISTEraseMEspam_OUTMITVMA.MIT.EDUEraseMEspam_OUTINTERNETEraseMEspam_OUTwtgw cc: Paper Mail: Subject: Re: [PIC]: Extending TMR2 *** WARNING *** This mail has originated outside your organization, either from an external partner or the Global Internet. Keep this in mind if you answer this message. >I'm currently using a 16f876 20Mhz. in an application. I need to delay an >output >between 0.06s and 0.003s. > >I have pre and post scaled to 16 on TMR2 but can only get a max. delay of >0.029s I >can not afford the overhead of waiting and counting interrupts. does anyone >have >any *smart* ideas to extend the time period? Maybe this isn't what you're looking for, since you haven't included any details about the function of your program, but, how about this: 1) Clear a flag bit when you set your output low (for example) 2) When you get your .029s interrupt, check the flag bit. If clear, set it. If set, then change your output high (2*.029s ~ .06s). Of course, you'd have to set your delay for 1/2 of what you need, then use the flag to double it. I'm not sure if you need better precision, but since you mentioned a range of .003s and .06s, this might be good enough. And you'd only have a .002s max error (assuming your max. delay possible is REALLY .0290 seconds) with the flag's doubling effect. --Andrew _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body ******************************************************************** This email and any attachments are confidential to the intended recipient and may also be privileged. If you are not the intended recipient please delete it from your system and notify the sender. You should not copy it or use it for any purpose nor disclose or distribute its contents to any other person. ******************************************************************** -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestEraseME.....mitvma.mit.edu

>interrupts will give higher resolution, but may cause me stack problems, >which is >what I am trying to avoid. If you're expecting to safely enter the ISR anyways because of the "normal" TMR2 interrupt, there's no reason to expect stack problems just because you're entering the ISR effectively twice as often. And you will LOSE resolution each time you go through the ISR (count more interrupts with a smaller TMR2 scale), you won't get higher resolution. --Andrew _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestEraseMEEraseMEmitvma.mit.edu

The instruction cycle time is 0.00000005s for a 20Mhz clock! and with both the post scale and pre-scale set to 16 you get a TMR2 resolution of 0.0000128s! Do you live near a black hole, where time is different from here? RemoveMEsnurplespam_OUTKILLspamHOTMAIL.COM on 18/10/2001 17:54:59 Please respond to RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDUTakeThisOuTspamINTERNETTakeThisOuTspamwtgw To: EraseMEPICLISTspamspamBeGoneMITVMA.MIT.EDUspamspamBeGoneINTERNETspamspamBeGonewtgw cc: Paper Mail: Subject: Re: [PIC]: Extending TMR2 *** WARNING *** This mail has originated outside your organization, either from an external partner or the Global Internet. Keep this in mind if you answer this message. >8bit resolution is fine, and a minimum resolution of approx. 0.00012 will >be fine. How can you expect to get a pulse resolution of .00012 if your instruction cycle time is .0002 at 20 MHz? _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestKILLspammitvma.mit.edu ******************************************************************** This email and any attachments are confidential to the intended recipient and may also be privileged. If you are not the intended recipient please delete it from your system and notify the sender. You should not copy it or use it for any purpose nor disclose or distribute its contents to any other person. ******************************************************************** -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

>The instruction cycle time is 0.00000005s for a 20Mhz clock! and with both >the post >scale and pre-scale set to 16 you get a TMR2 resolution of 0.0000128s! > >Do you live near a black hole, where time is different from here? The quadrature timing for instruction pipelining in the PIC line of products is a 4:1 ratio. That means a 1/20MHz * 4 = cycle time per instruction. 20MHz cycle time = 200ns = .2us I don't live near a black hole, but maybe your datasheets got sucked into one. --Andrew _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads