Post by thread:Using PIC16C71 A/D

Amey, The ADCON0 register is for conversion time. You are asking about sampling time. At 16kHz you would need to take an A/D reading every 62.5 microseconds. This is well within the settling time of the 16c71s A/D module. Use a timer interrupt set at your sampling rate to start the A/D conversion and then use the A/D interrupt to read the answer after the conversion is complete. Once the conversion is completed the channel will begin to recharge its internal RC circuit again after 2Tad which will still give you plenty of time for the reading to settle before your next sampling point. Bob -----Original Message----- From: Amey Deosthali <spam_OUTameyTakeThisOuTVISION.ECE.UTEXAS.EDU> To: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU <PICLISTKILLspamMITVMA.MIT.EDU> Date: Monday, January 26, 1998 2:42 PM Subject: Using PIC16C71 A/D {Quote hidden}>Hi, > >I am new to PIC programming. How do you use PIC16C71 A/D for sampling an >analog signal at 8Khz or 16Khz. The ADCON0 register seems to have scaling >factors of only 2,8 and 32.. > >Thanks, > >Amey Deosthali > > >

Hi all, I want to use the PIC16C71 A/D converter. Is it possible to use the 20Mhz clock to get 8-bit accuracy from A/D? The specifications say that if we use the 20Mhz clock, Tad is violated. Thanks, Amey ------------------------------------------------------------------------------- AMEY A. DEOSTHALI ------------------------------------------------------------------------------- Lab Address: Home Address: ESPL, ENS526E 3110 Red River, Apt # 208 Dept. of ECE Austin, TX 78705 University of Texas at Austin, Tel:(512)-499-8957 Austin, TX 78712 - 1084. Tel:(512)-232-2769 Email:.....ameyKILLspam.....vision.ece.utexas.edu Web :http://anchovy.ece.utexas.edu/~amey -------------------------------------------------------------------------------

Amey Deosthali <EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU> wrote: > I want to use the PIC16C71 A/D converter. Is it possible to use the > 20Mhz clock to get 8-bit accuracy from A/D? The specifications say > that if we use the 20Mhz clock, Tad is violated. There are two ways to solve this, Amey... 1. Set the A?D Clock Source to "internal RC" (ADCS0 and ADCS1 both set to "1"). This will give you a Tad of 2-6 uS (typically 4 uS), which is legal for the 16C71. 2. Use a 16C710 or 16C711 instead of the 16C71. The '710 and '711 have a minimum Tad of 1.6 uS, which means that you can use a 20 MHz clock and set the A/D Clock Source to "32Tosc" (ADCS1 = 1, ADCS0 = 0). -Andy === Andrew Warren - fastfwdspam_OUTix.netcom.com === Fast Forward Engineering - Vista, California === http://www.geocities.com/SiliconValley/2499

> You can run most of the pic's at higher speeds and they usually work > okay with no errors, > but.... you have to heatsink them or you might let the smoke out. Wow! Is the heat dissipation so high? I think I am not really clear about the working of the 16C71 A/D. According to what I understand there are two separate timings to take care of -- acquisition time and conversion time. Right? Suppose I want to sample an analog signal at 8Khz. So I want the A/D to take a sample every 125us and convert it. I can control the conversion by the GO/DONE bit (bit2 in ADCON0). How do I control the acquistion? I want the A/D to convert the sample which is taken every 125us. Do I do it by turning the ADON (bit 0 in ADCON0) bit on/off. What I was thinking of was to program the timer to give an interrupt every 125us. Then in the interrupt service routine, set the ADON bit to 1, wait for about 10us then start the conversion. After the conversion is complete, read the ADRES register and then turn off the A/D by turning of the ADON bit. After doing all the processing, return from the ISR and wait for the next interrupt. Is this procedure right? Thanks, Amey

On Thu, 29 Jan 1998 13:04:02 -0600 Amey Deosthali <@spam@ameyKILLspamvision.ece.utexas.edu> writes: >> You can run most of the pic's at higher speeds and they usually work >> okay with no errors, >> but.... you have to heatsink them or you might let the smoke out. > >Wow! Is the heat dissipation so high? No, it isn't. The PIC will just malfunction above a certain speed; it won't be damaged. > >I think I am not really clear about the working of the 16C71 A/D. >According to what I understand there are two separate timings to take >care >of -- acquisition time and conversion time. Right? Suppose I want to >sample an analog signal at 8Khz. So I want the A/D to take a sample >every >125us and convert it. I can control the conversion by the GO/DONE bit >(bit2 in ADCON0). How do I control the acquistion? The converter works (I think) by first charging a network of capacitors to the input voltage, then measuring the charge in each one as it is discharged. When you select a channel (all the input pins go through an analog multiplexer, then to the single ADC), the capacitors start charging. They have to be allowed to charge for a certain time in order to equalize to the voltage at the input. This is the acquisition time. When the GO bit is set, they are disconected from the input and the charge measured. The discharging sequence is controlled by the A/D converter clock and must be in the proper range to get an accurate conversion. The time required is the conversion time. If you only have one channel, just set the GO bit at regular intervals. Be sure the time between when the conversion is done and the next one starts is long enough to meet the acquisition time (i.e. sample period > acquisition time + conversion time). I want the A/D to >convert the sample which is taken every 125us. Do I do it by turning >the >ADON (bit 0 in ADCON0) bit on/off. No, leave this bit on all the time the converter is in use. If you aren't going to use the converter for a while (or not at all), turn it off to save a little power. > >What I was thinking of was to program the timer to give an interrupt >every >125us. The ISR just needs to read the ADRES register (getting the result of the last conversion), then set the GO bit to start the next one. This will convert the same channel over and over at regular times. _____________________________________________________________________ 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]