Post by thread:[PIC]: tmr0 on 16F84 interrupt period

Just double checking this. At 4MHz, the timer will interrupt every: 256((2^(prescaler+1)/(2^22)) seconds. So with a 0 prescalar you'll be getting an interrupt every: 256(2/(2^22)) seconds (122us)? This appears to be the smallest obtainable period with this clock speed. If anyone can confirm this, it'd be much appreciated!! Also, if someone has a better timer interrupt reference than the 16F84 data sheet, I'd appreciate that too. The datasheet merely says 1:2 .. 1:256 prescalars are available and I only assume that means clock/2^(prescale+1). Thanks! -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Nick Veys wrote: > > Just double checking this. At 4MHz, the timer will interrupt every: > 256((2^(prescaler+1)/(2^22)) seconds. So with a 0 prescalar you'll be > getting an interrupt every: 256(2/(2^22)) seconds (122us)? This appears to > be the smallest obtainable period with this clock speed. If anyone can > confirm this, it'd be much appreciated!! > > Also, if someone has a better timer interrupt reference than the 16F84 data > sheet, I'd appreciate that too. The datasheet merely says 1:2 .. 1:256 > prescalars are available and I only assume that means clock/2^(prescale+1). Hi Nick, no you can assign the prescaler to WDT, then the timer0 will inc with every instruction, ie, 1:1 ratio. It will interrupt on overflow every 256 instructions. The 16C84 manual has a lot of data not in the 16F84 or 16F84A datasheets. It has some nice diagrams about the ints and timer0 int latency. You can download from this page: http://www.ezy.net.au/~fastvid/16c84_man.pdf (right click on link to download it) -Roman -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

>Just double checking this. At 4MHz, the timer will interrupt every: >256((2^(prescaler+1)/(2^22)) seconds. So with a 0 prescalar you'll be >getting an interrupt every: 256(2/(2^22)) seconds (122us)? This appears to >be the smallest obtainable period with this clock speed. If anyone can >confirm this, it'd be much appreciated!! No, actually at 4MHz, TMR0 will interrupt every 256us with a 1:1 prescaler. >sheet, I'd appreciate that too. The datasheet merely says 1:2 .. 1:256 >prescalars are available and I only assume that means clock/2^(prescale+1). The datasheet says that the minimum prescale value for TMR0 is 1:2 when assigned to TMR0. To achieve a 1:1 scale for TMR0, assign the prescaler to the WDT instead of TMR0. --Andrew _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> Just double checking this. At 4MHz, the timer will interrupt every: > 256((2^(prescaler+1)/(2^22)) seconds. So with a 0 prescalar you'll be > getting an interrupt every: 256(2/(2^22)) seconds (122us)? This appears to > be the smallest obtainable period with this clock speed. If anyone can > confirm this, it'd be much appreciated!! I didn't follow where you got your numbers from. But, the fastest free running timer 0 interrupt will be every 256 instructions, which is every 256uS with a 4MHz oscillator. ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, spam_OUTolinTakeThisOuTembedinc.com, http://www.embedinc.com -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Nick, If you have no prescaler and you write 255 to the TMR0 register, you can get an interrupt in 3us I believe. It may be slightly more than that, but not much. I get this from the fact that writing a value (255) to TMR0 means the next clock will overflow it. But, since you wrote to it, there is a two cycle delay before it increments again because it has to synchronize. Therefore 3us. If this is wrong, I'm sure someone will correct me. I'm recalling this from memory because I don't have the datasheet in front of me. So don't be too harsh if I'm not completely correct. Regards, Jim On Thu, 26 April 2001, Nick Veys wrote: {Quote hidden}> > Just double checking this. At 4MHz, the timer will interrupt every: > 256((2^(prescaler+1)/(2^22)) seconds. So with a 0 prescalar you'll be > getting an interrupt every: 256(2/(2^22)) seconds (122us)? This appears to > be the smallest obtainable period with this clock speed. If anyone can > confirm this, it'd be much appreciated!! > > Also, if someone has a better timer interrupt reference than the 16F84 data > sheet, I'd appreciate that too. The datasheet merely says 1:2 .. 1:256 > prescalars are available and I only assume that means clock/2^(prescale+1). > > Thanks! > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads .....jimKILLspam@spam@jpes.com -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

James, You have the right idea here. The better idea is to ADD a value to TMR0 in your interrupt handler. This avoids issues with interrupt timing jitter. Assuming no prescaler, the actual interrupt rate will be every: 256 - (Value_Added - 2) Instructions. One particularly useful case: movlw 8 addwf TMR0 This will result in an interrupt every 250 instructions (250 uSec at 4MHz clock, or exactly 4000 interrupts per second). Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) {Original Message removed}

Ok, so I have the clock coming in @ 4MHz, effectively 1MHz to the processor. If I set the prescalar to 1 and assign it to the WDT I'll get a 1:1 prescalar and an interrupt every ~244us. Now I know that I can add to that value to speed it up so that's good, but my one problem with this is, I don't want to use the Watchdog timer... If I have it disabled but still assign the prescalar to the watchdog, will it be disabled? The /only/ interrupt I want is the tmr0 one. {Quote hidden}> >Just double checking this. At 4MHz, the timer will interrupt every: > >256((2^(prescaler+1)/(2^22)) seconds. So with a 0 prescalar you'll be > >getting an interrupt every: 256(2/(2^22)) seconds (122us)? This > appears to > >be the smallest obtainable period with this clock speed. If anyone can > >confirm this, it'd be much appreciated!! > > No, actually at 4MHz, TMR0 will interrupt every 256us with a 1:1 > prescaler. > > >sheet, I'd appreciate that too. The datasheet merely says 1:2 .. 1:256 > >prescalars are available and I only assume that means > clock/2^(prescale+1). > > The datasheet says that the minimum prescale value for TMR0 is 1:2 when > assigned to TMR0. To achieve a 1:1 scale for TMR0, assign the > prescaler to > the WDT instead of TMR0. > > --Andrew -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Nick, If the prescaler is not assigned to TMR0, then TMR0 will be at 1:1. If it is assigned to the WD timer, but the WD timer is not used, then there are no consequences. Regards, Jim On Fri, 27 April 2001, Nick Veys wrote: {Quote hidden}> > Ok, so I have the clock coming in @ 4MHz, effectively 1MHz to the processor. > If I set the prescalar to 1 and assign it to the WDT I'll get a 1:1 > prescalar and an interrupt every ~244us. Now I know that I can add to that > value to speed it up so that's good, but my one problem with this is, I > don't want to use the Watchdog timer... If I have it disabled but still > assign the prescalar to the watchdog, will it be disabled? The /only/ > interrupt I want is the tmr0 one. > > > >Just double checking this. At 4MHz, the timer will interrupt every: > > >256((2^(prescaler+1)/(2^22)) seconds. So with a 0 prescalar you'll be > > >getting an interrupt every: 256(2/(2^22)) seconds (122us)? This > > appears to > > >be the smallest obtainable period with this clock speed. If anyone can > > >confirm this, it'd be much appreciated!! > > > > No, actually at 4MHz, TMR0 will interrupt every 256us with a 1:1 > > prescaler. > > > > >sheet, I'd appreciate that too. The datasheet merely says 1:2 .. 1:256 > > >prescalars are available and I only assume that means > > clock/2^(prescale+1). > > > > The datasheet says that the minimum prescale value for TMR0 is 1:2 when > > assigned to TMR0. To achieve a 1:1 scale for TMR0, assign the > > prescaler to > > the WDT instead of TMR0. > > > > --Andrew > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads jimKILLspamjpes.com -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

part 0 44 bytes his is a multi-part message in MIME format. part 1 1912 bytes content-type:text/plain; charset=us-ascii (decoded 7bit) Nick Veys wrote: > Ok, so I have the clock coming in @ 4MHz, effectively 1MHz to the processor. > If I set the prescalar to 1 and assign it to the WDT I'll get a 1:1 > prescalar and an interrupt every ~244us. if you are using TMR0 as a free running timer (without prescaler), then it will set its interrupt flag every 256 us > Now I know that I can add to that > value to speed it up so that's good, but my one problem with this is, I > don't want to use the Watchdog timer... If I have it disabled but still > assign the prescalar to the watchdog, will it be disabled? The /only/ > interrupt I want is the tmr0 one. > As long as you keep the watchdog timer disabled, you will never get a WDT reset. {Quote hidden}> > > >Just double checking this. At 4MHz, the timer will interrupt every: > > >256((2^(prescaler+1)/(2^22)) seconds. So with a 0 prescalar you'll be > > >getting an interrupt every: 256(2/(2^22)) seconds (122us)? This > > appears to > > >be the smallest obtainable period with this clock speed. If anyone can > > >confirm this, it'd be much appreciated!! > > > > No, actually at 4MHz, TMR0 will interrupt every 256us with a 1:1 > > prescaler. > > > > >sheet, I'd appreciate that too. The datasheet merely says 1:2 .. 1:256 > > >prescalars are available and I only assume that means > > clock/2^(prescale+1). > > > > The datasheet says that the minimum prescale value for TMR0 is 1:2 when > > assigned to TMR0. To achieve a 1:1 scale for TMR0, assign the > > prescaler to > > the WDT instead of TMR0. > > > > --Andrew > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads part 2 422 bytes content-type:text/x-vcard; charset=us-ascii; (decoded quoted-printable) begin:vcard n:Romero Plaza;P�vel Ernesto tel;cell:5489528 tel;fax:6-7444829 tel;home:6-7464233 tel;work:6-7444829 x-mozilla-html:TRUE url:http://www.insitel.com.co org:Insitel Ltda.;Research & Development adr:;;Calle 21 # 16 - 46 Piso 7;Armenia;Quind�o;;Colombia version:2.1 email;internet:.....promeroKILLspam.....insitel.com.co title:Hardware Engineer fn:P�vel Ernesto Romero Plaza end:vcard part 3 154 bytes -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

----- Original Message ----- From: "Nick Veys" <EraseMEnickspam_OUTTakeThisOuTVEYS.COM> To: <PICLISTspam_OUTMITVMA.MIT.EDU> Sent: Friday, April 27, 2001 11:45 AM Subject: Re: [PIC]: tmr0 on 16F84 interrupt period > Ok, so I have the clock coming in @ 4MHz, effectively 1MHz to the processor. > If I set the prescalar to 1 and assign it to the WDT I'll get a 1:1 > prescalar and an interrupt every ~244us. Now I know that I can add to that > value to speed it up so that's good, but my one problem with this is, I > don't want to use the Watchdog timer... If I have it disabled but still > assign the prescalar to the watchdog, will it be disabled? The /only/ > interrupt I want is the tmr0 one. By default after power on, the prescaler is assigned to WDT (OPTION_REG is initialized to all ones after POR). Changing assignment(OPTION_REG, PSA) or value(OPTION_REG PS0,PS1,PS2) of prescaler does not affect whether WDT is enabled. If the config bit is set during programming so that WDT is disabled(WDTE cleared), then it is disabled.<-(period) By the way, in terms of TMR0 the prescaler cannot be set to one. Once it is assigned to TMR0, the prescaler is automatically at least two (with all bits cleared). The way it is set to one is by assigning it to the WDT. In which case you should receive an interrupt roughly every 256 us from TMR0. Provided that you re-enable them everytime, that is. :-) If you write to TMR0 then it will not start incrementing for two machine cycles. {Quote hidden}> > > >Just double checking this. At 4MHz, the timer will interrupt every: > > >256((2^(prescaler+1)/(2^22)) seconds. So with a 0 prescalar you'll be > > >getting an interrupt every: 256(2/(2^22)) seconds (122us)? This > > appears to > > >be the smallest obtainable period with this clock speed. If anyone can > > >confirm this, it'd be much appreciated!! > > > > No, actually at 4MHz, TMR0 will interrupt every 256us with a 1:1 > > prescaler. > > > > >sheet, I'd appreciate that too. The datasheet merely says 1:2 .. 1:256 > > >prescalars are available and I only assume that means > > clock/2^(prescale+1). > > > > The datasheet says that the minimum prescale value for TMR0 is 1:2 when > > assigned to TMR0. To achieve a 1:1 scale for TMR0, assign the > > prescaler to > > the WDT instead of TMR0. > > > > --Andrew > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Excellent, thanks to all who helped clear this up for me! {Quote hidden}> -----Original Message----- > From: pic microcontroller discussion list > [@spam@PICLISTKILLspamMITVMA.MIT.EDU]On Behalf Of promero > Sent: Friday, April 27, 2001 12:09 PM > To: KILLspamPICLISTKILLspamMITVMA.MIT.EDU > Subject: Re: [PIC]: tmr0 on 16F84 interrupt period > > > > > Nick Veys wrote: > > > Ok, so I have the clock coming in @ 4MHz, effectively 1MHz to > the processor. > > If I set the prescalar to 1 and assign it to the WDT I'll get a 1:1 > > prescalar and an interrupt every ~244us. > > if you are using TMR0 as a free running timer (without > prescaler), then it will > set its interrupt flag every 256 us > > > Now I know that I can add to that > > value to speed it up so that's good, but my one problem with this is, I > > don't want to use the Watchdog timer... If I have it disabled but still > > assign the prescalar to the watchdog, will it be disabled? The /only/ > > interrupt I want is the tmr0 one. > > > > As long as you keep the watchdog timer disabled, you will never > get a WDT reset. > > > > > > >Just double checking this. At 4MHz, the timer will interrupt every: > > > >256((2^(prescaler+1)/(2^22)) seconds. So with a 0 prescalar > you'll be > > > >getting an interrupt every: 256(2/(2^22)) seconds (122us)? This > > > appears to > > > >be the smallest obtainable period with this clock speed. If > anyone can > > > >confirm this, it'd be much appreciated!! > > > > > > No, actually at 4MHz, TMR0 will interrupt every 256us with a 1:1 > > > prescaler. > > > > > > > >sheet, I'd appreciate that too. The datasheet merely says > 1:2 .. 1:256 > > > >prescalars are available and I only assume that means > > > clock/2^(prescale+1). > > > > > > The datasheet says that the minimum prescale value for TMR0 > is 1:2 when > > > assigned to TMR0. To achieve a 1:1 scale for TMR0, assign the > > > prescaler to > > > the WDT instead of TMR0. > > > > > > --Andrew > > > > -- > > http://www.piclist.com hint: PICList Posts must start with ONE topic: > > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

----- Original Message ----- From: "Nick Veys" <RemoveMEnickTakeThisOuTVEYS.COM> To: <spamBeGonePICLISTspamBeGoneMITVMA.MIT.EDU> Sent: Friday, April 27, 2001 12:45 PM Subject: Re: [PIC]: tmr0 on 16F84 interrupt period > Ok, so I have the clock coming in @ 4MHz, effectively 1MHz to the processor. > If I set the prescalar to 1 and assign it to the WDT I'll get a 1:1 > prescalar and an interrupt every ~244us. Now I know that I can add to that > value to speed it up so that's good, but my one problem with this is, I > don't want to use the Watchdog timer... If I have it disabled but still > assign the prescalar to the watchdog, will it be disabled? The /only/ > interrupt I want is the tmr0 one. Yes it will be disabled. Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

>Ok, so I have the clock coming in @ 4MHz, effectively 1MHz to the >processor. >If I set the prescalar to 1 and assign it to the WDT I'll get a 1:1 >prescalar and an interrupt every ~244us. Now I know that I can add to that Where are you getting these numbers (i.e. ~244us)? Like I said, the interrupt will occur every 256us at 4MHz. There's no approximation, no guesswork. It's 256us. 4Mhz/4 (quadrature) = 1MHz per cycle. 1/1,000,000 = 1us per cycle. TMR0 ranges from 0-255 (256 steps). 256*1us per cycle = 256us. >value to speed it up so that's good, but my one problem with this is, I >don't want to use the Watchdog timer... If I have it disabled but still >assign the prescalar to the watchdog, will it be disabled? The /only/ >interrupt I want is the tmr0 one. This is fine. If you disable the WDT, it's off. Doesn't matter what you assign to it for value, prescale, whatever. It's disabled. Check the datasheet... the 16F84 has a pretty decent datasheet if I remember correctly. --Andrew _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> Ok, so I have the clock coming in @ 4MHz, effectively 1MHz to the processor. > If I set the prescalar to 1 and assign it to the WDT I'll get a 1:1 > prescalar and an interrupt every ~244us. 256uS actually. How on earth did you get 244us? > Now I know that I can add to that > value to speed it up so that's good, but my one problem with this is, I > don't want to use the Watchdog timer... If I have it disabled but still > assign the prescalar to the watchdog, will it be disabled? You really need to so some manual reading. Check out the section about assigning the prescaler to the watchdog timer. What does it say, if anything, about the assignment effecting whether the watchdog is enabled or not? Read the watchdog timer section. What if anything does it say about the watchdog enable being effected by the prescaler assignment? Also read the section on the configuration bits. If you still have questions after doing this homework, I'll try to help. ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, TakeThisOuTolinEraseMEspam_OUTembedinc.com, http://www.embedinc.com -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> > Ok, so I have the clock coming in @ 4MHz, effectively 1MHz to the > processor. > > If I set the prescalar to 1 and assign it to the WDT I'll get a 1:1 > > prescalar and an interrupt every ~244us. > > 256uS actually. How on earth did you get 244us? Heh, been doing binary math for the past two weeks and my brain was stuck on Meg = 2^20 :) 10^6 is much easier and makes more sense, glad you guys corrected me on that one... {Quote hidden}> > Now I know that I can add to that > > value to speed it up so that's good, but my one problem with this is, I > > don't want to use the Watchdog timer... If I have it disabled but still > > assign the prescalar to the watchdog, will it be disabled? > > You really need to so some manual reading. Check out the section about > assigning the prescaler to the watchdog timer. What does it say, if > anything, about the assignment effecting whether the watchdog is > enabled or > not? Read the watchdog timer section. What if anything does it say about > the watchdog enable being effected by the prescaler assignment? Also read > the section on the configuration bits. If you still have questions after > doing this homework, I'll try to help. 16F84 manual doesn't even have the bit settings for the prescalars, I had to assume the values, although it was in the mid-range reference manual... It also says nothing about the watchdog timer being affected by the prescalar assignment, it's absolutely terrible in it's information actually... I don't ask until I've tried all other avenues :) -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

----- Original Message ----- From: "Nick Veys" <RemoveMEnickTakeThisOuTVEYS.COM> To: <PICLISTEraseME.....MITVMA.MIT.EDU> Sent: Friday, April 27, 2001 5:13 PM <SNIP> > 16F84 manual doesn't even have the bit settings for the prescalars, I had to > assume the values, although it was in the mid-range reference manual... It > also says nothing about the watchdog timer being affected by the prescalar > assignment, it's absolutely terrible in it's information actually... I don't > ask until I've tried all other avenues :) Make sure you have Microchip literature number 35007a (68 pages). Its all in there. :-) > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Nick Veys wrote: > 16F84 manual doesn't even have the bit settings for the prescalars, See datasheet (30430c, and/or 35007a for 16F84A) page 16 > I had to assume the values, although it was in the mid-range > reference manual... It also says nothing about the watchdog > timer being affected by the prescalar assignment, See datasheet (30430c) pages 27-31, 38, 39, 51 > it's absolutely terrible in it's information actually... > I don't ask until I've tried all other avenues :) Try reading the instructions... (Appologies if I seem a bit terse, but its been a long week) David W. Gulley Destiny Designs -- 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

> 16F84 manual doesn't even have the bit settings > for the prescalars, Section 4.2.2.2, page 16, bits 2-0, "Prescaler Rate Select bits". > It also says nothing about the watchdog timer being > affected by the prescalar assignment, Right, that's because it isn't. You can't expect the manual to list all the things the chip DOESN'T do, except in some confusing cases where one could make a reasonable but incorrect assumption. This is not one of those. > it's absolutely terrible in it's information actually... Personally, I find the Microchip documentation quite reasonable. Of course it helps to have actually read it. ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, EraseMEolinembedinc.com, http://www.embedinc.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