Post by thread:Resistance measurement progress

Thanks to all who replied to my plea for help. No-one seemed to have a convincing answer as to why the code in AN512 configured the timer 0 as a counter and then polled the TMR0 regsister. I decided just to poll RA4 as a normal input, and (this bit of) my code is now working fine. The schmitt trigger is still used so I can't see any reason not to use this method, and it means timer 0 is free for other purposes (as long as you don't want to use external clock) Most of my headaches came from the Read Modify Write instructions on ports that were driving a mosfet H-bridge, I guess the gate capacitance was slowing things down a bit. Nothing that a coupla NOPs didn't sort. My last remaining bug is the PWM (CCP1) output latching up. I can't set the PWM output to maximum as the output is AC coupled to a diode pump so it would stop working. I limit the maximum value I send to the CCPRL1 register, but occaisionally the output gets stuck high. When you do a RMW instruction on port C with the PWM active, does the micro read back the current state of the PWM output? If it happens to be high I guess a 1 could be written back to the output register? I can't believe this is the case as it would make using the port a nightmare. My employers decided that buying an ICEPIC2 emulator (with real time trace) would speed things up on the development front, so I should have a new toy to play with this week! Anything I should watch out for when using this or any problems that anyone knows of? Regards Mike Rigby-jones spam_OUTmrjonesTakeThisOuTnortel.co.uk

On Mon, 20 Jul 1998 09:04:53 +0100 "Rigby-Jones, Michael [PAI01:4837:EXCH]" <.....michael.rigby-jones.mrjonesKILLspam@spam@NORTEL.CO.UK> writes: >Thanks to all who replied to my plea for help. > >No-one seemed to have a convincing answer as to why the code in AN512 >configured the timer 0 as a counter and then polled the TMR0 >regsister. Convincing answer: The AN was developed for a PIC16C5X. These PICs do not have the timer pin connected to the PORTA register. The only way to determine the state of that pin is to examine its effect on the timer. The 14-bit PICs have the pin connected to both the timer and to the PORTA register. The input signal passes through the same Schmitt-trigger buffer no matter which way you read it. > >I decided just to poll RA4 as a normal input, and (this bit of) my >code is >now working fine. The schmitt trigger is still used so I can't see >any >reason not to use this method, and it means timer 0 is free for other >purposes (as long as you don't want to use external clock) The reason to not use it is that with PIC16C5X's you can't. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]

> Thanks to all who replied to my plea for help. > > No-one seemed to have a convincing answer as to why the code in > AN512 configured the timer 0 as a counter and then polled the TMR0 > regsister. > Let's see. I believe that the idea was to zero out TMR0, then begin chargeing the capacitor-rewsistor. Count the time going by, and periodically look at the TMR0 counter input. if the input is trpped, then the RC circuit has charged up to the schmidt trigger voltage. Does that address your question? > My employers decided that buying an ICEPIC2 emulator (with real time > trace) would speed things up on the development front, so I should > have a new toy to play with this week! Anything I should watch out > for when using this or any problems that anyone knows of? > God for them! You'll find that ICEPICs may be more finicky than regular PICs about power supplies. I had to put a special regulator instead of the cheesy, sleazy zener diode that passes for a power supply on my regular production boards. ICEPICS also instoduce a little capacitance in the probe, and tend to run a slightly different clock frequencies because of that. Other than that I've had good luck. -- Lawrence Lile "An Engineer is simply a machine for turning coffee into assembler code." Download AutoCad blocks for electrical drafting at: http://home1.gte.net/llile/index.htm