Post by thread:[PIC:] Analog to Digital Coversion Problems (pic16

I've tried to measure DC and display the corresponding number from the ADC on a LCD .I used pic16F877. For initiation of the ADC I used AN546. But when I'm changing the voltage gradually from 0V to 5V the LCD shows only four values respectivly : 0, 257, 514, 771. Where is the culprit? __________________________________ Do you Yahoo!? Yahoo! Mail Address AutoComplete - You start. We finish. http://promotions.yahoo.com/new_mail -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

Stefan_d6, Are you using all 10 bits? and do tou have the result left justified or right justified? If you are using all 10 bits and have it right justified, and are using the ms BYTE, the values displayed would be 0, 256, 512, 768. And your numbers are very close to these. The reason is you're only displaying the two most significant bits. Check your A/D setup and try displaying the LS byte only. It should go smoothly between 0 and 255. Once you get this part working, then you can deal with the two MS bits. Hope this helps. Regards, Jim {Quote hidden}> I've tried to measure DC and display the corresponding > number from the ADC on a LCD .I used pic16F877. For > initiation of the ADC I used AN546. > But when I'm changing the voltage gradually from 0V > to 5V the LCD shows only four values respectivly : 0, > 257, 514, 771. > Where is the culprit? > > > > __________________________________ > Do you Yahoo!? > Yahoo! Mail Address AutoComplete - You start. We finish. > http://promotions.yahoo.com/new_mail > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Stefan, Check the left/right justification of the result as set by ADCON1, bit 7. If you plan to use all 10 bits of the result, then your result should be right-justified so set this bit. Your conversion result will be in ADRESH:ADRESL as follows: 000000xx:xxxxxxxx where '0' are the leading zeros in front of the result and 'x' represents the conversion result. But be careful with ADRESL; the low byte of the result. It is in Bank1 so you need to change STATUS, RP0 to access it. Andrew akieran_at_ureach.com ________________________________________________ Get your own "800" number Voicemail, fax, email, and a lot more http://www.ureach.com/reg/tag ---- On , dimov stefan (.....stefan_d6KILLspam.....YAHOO.COM) wrote: {Quote hidden}> I've tried to measure DC and display the corresponding > number from the ADC on a LCD .I used pic16F877. For > initiation of the ADC I used AN546. > But when I'm changing the voltage gradually from 0V > to 5V the LCD shows only four values respectivly : 0, > 257, 514, 771. > Where is the culprit? > > > > __________________________________ > Do you Yahoo!? > Yahoo! Mail Address AutoComplete - You start. We finish. > http://promotions.yahoo.com/new_mail > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

In message <@spam@20040618203124.39691.qmailKILLspamweb51909.mail.yahoo.com>> dimov stefan <KILLspamstefan_d6KILLspamYAHOO.COM> wrote: > I've tried to measure DC and display the corresponding > number from the ADC on a LCD .I used pic16F877. For > initiation of the ADC I used AN546. > But when I'm changing the voltage gradually from 0V > to 5V the LCD shows only four values respectivly : 0, > 257, 514, 771. > Where is the culprit? Can you post your code here? It sounds like you're not setting the A/D up correctly, or you're not reading the A/D value correctly. Later. -- Phil. | Acorn Risc PC600 Mk3, SA202, 64MB, 6GB, RemoveMEphilpemTakeThisOuTdsl.pipex.com | ViewFinder, 10BaseT Ethernet, 2-slice, http://www.philpem.dsl.pipex.com/ | 48xCD, ARCINv6c IDE, SCSI ... Procrastination means never having to say you're sorry. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistservspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body

how are you converting the ADC result for LCD reading? Can you make a different interface to read that? RS232 to a terminal PC? Francisco dimov stefan wrote: {Quote hidden}>I've tried to measure DC and display the corresponding >number from the ADC on a LCD .I used pic16F877. For >initiation of the ADC I used AN546. > But when I'm changing the voltage gradually from 0V >to 5V the LCD shows only four values respectivly : 0, >257, 514, 771. > Where is the culprit? > > > >__________________________________ >Do you Yahoo!? >Yahoo! Mail Address AutoComplete - You start. We finish. >http://promotions.yahoo.com/new_mail > >-- >http://www.piclist.com#nomail Going offline? Don't AutoReply us! >email TakeThisOuTlistservEraseMEspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body > >. > > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

I think Chris has nailed it. This oupute described could easily result from reading the ADRESH register twice. The most likely reason for this is failure to switch banks. ADRESH and ADRESL are at the same address; except one (ADRESH) is in bank 0 and the other (ADRESL), is in bank1. To use the lower eight bits, use: bsf STATUS, RP0 ; switch to Bank1 movf ADRESL ^ 0x80, W bcf STATUS, RP0 ; switch to Bank0 Then you'll have ADRESL in the w register. Andrew ________________________________________________ Get your own "800" number Voicemail, fax, email, and a lot more http://www.ureach.com/reg/tag ---- On , Chris Emerson (EraseMEpicNOSREME.ORG) wrote: > On Fri, Jun 18, 2004 at 01:31:24PM -0700, dimov stefan wrote: > > But when I'm changing the voltage gradually from 0V > > to 5V the LCD shows only four values respectivly : 0, > > 257, 514, 771. > > Where is the culprit? > > I bet there's a typo, and you're using ADRESH twice instead of > ADRESH:ADRESL. Those numbers in hex are 0x0000, 0x0101, 0x0202, and 0x0303, > which look rather suspicious. > > Chris > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email RemoveMElistservEraseMEEraseMEmitvma.mit.edu with SET PICList DIGEST in the body > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservspam_OUTKILLspammitvma.mit.edu with SET PICList DIGEST in the body

OK, I fixed the flaws as Chris and Andrew said.To read the ADRESH:ADRESL I used the following code: bsf STATUS,RP0 ;bank 1 movf ADRESL,W movwf L_byte bcf STATUS,RP0 ;bank 0 movf ADRESH,W movwf H_byte ;L_byte and H_byte are registers where the result ;is stored and then transformed to BCD using four ;additional registers-R0,R1,R2,R3.These registers ;(numbers) are displayed on the LCD but the result wasn't too encouraging - the LCD showed correspondingly 0000,0256,0512 and 0768 ,i.e. only the two bits of the ADRESH. When I used only ADRESL (H_byte=0) the LCD showed 0000 regardless of changing the voltage from 0V to 5V. So,I think the ADRESL is always empty.I don't know why! The following is the Initiation of the ADC: InitADC bsf STATUS,RP0 ;bank 1 movlw B'10000000' ;right justif. movwf ADCON1 ;all Analog clrf ADRESL bcf STATUS,RP0 ;bank 0 movlw B'11000001' ;RC osc,ch 0(RA0), movwf ADCON0 ;Conv. stopped,ADC ON clrf ADRESH return Any ideas? Bye Stefan --- Andrew Kieran <RemoveMEakieranTakeThisOuTspamUREACH.COM> wrote: {Quote hidden}> I think Chris has nailed it. This oupute described > could easily > result from reading the ADRESH register twice. The > most likely > reason for this is failure to switch banks. ADRESH > and ADRESL > are at the same address; except one (ADRESH) is in > bank 0 and > the other (ADRESL), is in bank1. > > To use the lower eight bits, use: > > bsf STATUS, RP0 ; switch to > Bank1 > movf ADRESL ^ 0x80, W > bcf STATUS, RP0 ; switch to > Bank0 > > Then you'll have ADRESL in the w register. > > Andrew > > > > ________________________________________________ > Get your own "800" number > Voicemail, fax, email, and a lot more > http://www.ureach.com/reg/tag > > > ---- On , Chris Emerson (EraseMEpicspamspamBeGoneNOSREME.ORG) wrote: > > > On Fri, Jun 18, 2004 at 01:31:24PM -0700, dimov > stefan wrote: > > > But when I'm changing the voltage gradually > from 0V > > > to 5V the LCD shows only four values respectivly > : 0, > > > 257, 514, 771. > > > Where is the culprit? > > > > I bet there's a typo, and you're using ADRESH > twice instead of > > ADRESH:ADRESL. Those numbers in hex are 0x0000, > 0x0101, > 0x0202, and 0x0303, > > which look rather suspicious. > > > > Chris > > > > -- > > http://www.piclist.com#nomail Going offline? Don't > AutoReply > us! > > email RemoveMElistservKILLspammitvma.mit.edu with SET PICList > DIGEST in the > body > > > > > > -- > http://www.piclist.com#nomail Going offline? Don't > AutoReply us! > email listservSTOPspamspam_OUTmitvma.mit.edu with SET PICList > DIGEST in the body > __________________________________ Do you Yahoo!? Yahoo! Mail - 50x more storage than other providers! http://promotions.yahoo.com/new_mail -- http://www.piclist.com hint: To leave the PICList spamBeGonepiclist-unsubscribe-requestSTOPspamEraseMEmitvma.mit.edu

On Sat, Jun 19, 2004 at 03:00:07AM -0700, dimov stefan wrote: > OK, I fixed the flaws as Chris and Andrew said.To read > the ADRESH:ADRESL I used the following code: > > bsf STATUS,RP0 ;bank 1 > movf ADRESL,W > movwf L_byte > > bcf STATUS,RP0 ;bank 0 > movf ADRESH,W > movwf H_byte Where are L_byte and H_byte? If they're in banked areas, don't forget the bank bits need to be right when accessing them too. I bet you're writing the ADRESL value to a register in bank 1, but then reading the corresponding addressin bank 0 later (which was never written to) when doing the BCD conversion. The easiest way to avoid banking problems like this is to use "banksel" before every register access: banksel ADRESL movf ADRESL, W banksel L_byte movwf L_byte banksel ADRESH movf ADRESH, W banksel H_byte movwf H_byte That way banking errors are much less likely. Doing this will usually increase the code size, but it's not worth worrying about that until you start running out of code space. Chris -- http://www.piclist.com hint: To leave the PICList @spam@piclist-unsubscribe-request@spam@spam_OUTmitvma.mit.edu