Post by thread:[PIC] Reading an input

Hi Grant, The function will always return 0. Also, no need to use asm. You could write it like this: unsigned char ReadPort_A_Bit(unsigned char BitReq){ return (BitReq & PORTA); } and test the return for nonzero. Cheerful regards, Bob Grant Brown wrote: {Quote hidden}> Hi List, > > Target device 16F84 (soon to be replaced with a 16F88) > > I know this will be the simplest thing but I can't seem to get it to work. > > I am trying to set up PortA pin 1 as an input then read a push button > > So I have Initialized the port with > > PORTA = 0; > TRISA = 0x3; // outputs except RA0 and RA1,which is set to input > > PORTB = 0; > TRISB = 0; // set as all outputs > > And to read the port pin I have a function that I use, > > char ReadPort_A_Bit(unsigned int BitReq) > { > return 0; > #asm > BANKSEL PORTA; // select bnak for port A > BTFSS PORTA BitReq; // read the bit value > return 1; > #endasm > } > > But it does not seem to be working so could someone point me in the > right direction. >

Hi Bob, Thanks for that, Just to add to my learning why does it always return 0 ? I thought the idea with BTFSS was that it skipped the next instruction only if the bit was not set ie 0 Does return not act as a temporary variable until the function exits ? Kind regards Grant Brown Bob Blick wrote: {Quote hidden}> Hi Grant, > > The function will always return 0. > > Also, no need to use asm. > > You could write it like this: > > unsigned char ReadPort_A_Bit(unsigned char BitReq){ > return (BitReq & PORTA); > } > > and test the return for nonzero. > > Cheerful regards, > > Bob > > > Grant Brown wrote: > >> Hi List, >> >> Target device 16F84 (soon to be replaced with a 16F88) >> >> I know this will be the simplest thing but I can't seem to get it to work. >> >> I am trying to set up PortA pin 1 as an input then read a push button >> >> So I have Initialized the port with >> >> PORTA = 0; >> TRISA = 0x3; // outputs except RA0 and RA1,which is set to input >> >> PORTB = 0; >> TRISB = 0; // set as all outputs >> >> And to read the port pin I have a function that I use, >> >> char ReadPort_A_Bit(unsigned int BitReq) >> { >> return 0; >> #asm >> BANKSEL PORTA; // select bnak for port A >> BTFSS PORTA BitReq; // read the bit value >> return 1; >> #endasm >> } >> >> But it does not seem to be working so could someone point me in the >> right direction. >> >> -- Kind Regards Grant Brown SiteDoc Pty Ltd mob: 0412 926 995 http://www.sitedoc.com.au __________________________________________________________________________________________________________ This email message together with any attachments is intended only for the addressee(s) and contains information that may be confidential and/or copyright. If you are not the intended recipient, please notify the sender by reply email (or telephone SiteDoc Pty Ltd on +61 2 42291185) and immediately delete this email together with any attachments from your computer. If you are the intended recipient, you must not copy, disclose, reproduce or distribute this communication together with any attachments without the authority of SiteDoc Proprietary Limited. No representation is made that this email or any attachments are free of viruses. Virus scanning is recommended and is the responsibility of the recipient. Unless specifically stated by the sender as the views of SiteDoc Proprietary Limited, any views expressed in this message are those of the individual sender, and no responsibility will be borne by SiteDoc Proprietary Limited for its content or outcomes.

Hi Forrest, Not much in C but 20 odd years in Delphi. I think I was confusing "return" with "Result" in Delphi which does act as a temporary variable until the function exits. so for the given function below is the way I have re-written it correct - so in other words do I just * declare a local variable * assign it a value * then return the local variable eg, char ReadPort_A_Bit(unsigned int BitReq) { char temp = 0; #asm BANKSEL PORTA; // select bnak for port A BTFSS PORTA BitReq; // read the bit value Temp = 1; #endasm Return temp } Kind regards Grant Brown Forrest W Christian wrote: {Quote hidden}> Grant Brown wrote: > >> Just to add to my learning why does it always return 0 ? >> >> > Here's your answer: > >> Does return not act as a temporary variable until the function exits ? >> >> > No, return immediately exits from the function and returns the value shown. > > I take it you haven't written much code in C... is there another > language you are more familiar with? > > -forrest > > -- Kind Regards Grant Brown SiteDoc Pty Ltd mob: 0412 926 995 http://www.sitedoc.com.au __________________________________________________________________________________________________________ This email message together with any attachments is intended only for the addressee(s) and contains information that may be confidential and/or copyright. If you are not the intended recipient, please notify the sender by reply email (or telephone SiteDoc Pty Ltd on +61 2 42291185) and immediately delete this email together with any attachments from your computer. If you are the intended recipient, you must not copy, disclose, reproduce or distribute this communication together with any attachments without the authority of SiteDoc Proprietary Limited. No representation is made that this email or any attachments are free of viruses. Virus scanning is recommended and is the responsibility of the recipient. Unless specifically stated by the sender as the views of SiteDoc Proprietary Limited, any views expressed in this message are those of the individual sender, and no responsibility will be borne by SiteDoc Proprietary Limited for its content or outcomes.

Grant Brown wrote: > Not much in C but 20 odd years in Delphi. > You may want to look at mikropascal then... http://www.mikroe.com/en/compilers/mikropascal/pic/ . I'm not trying to discourage you from learning C... but learning C on a PIC should be an interesting experience.... One thing you need to keep in mind is that a PIC is EXTREMELY resource limited, and there are things you would normally do which will fail miserably on a PIC, just because of lack of code and or data space - even though the compiler is perfectly happy to let you try. > I think I was confusing "return" with "Result" in Delphi which does act > as a temporary variable until the function exits. > Yep... That's why I caught the not a lot of C.... Anyone who's written much C would have caught this mistake :) ... But again, I've put a few semicolons in the wrong spot and couldn't figure out why it was always executing a block (or not). > so for the given function below is the way I have re-written it correct > - so in other words do I just > > * declare a local variable > * assign it a value > * then return the local variable > For programming efficiency, I'd recommend using an early return instead of a scratch variable. There are two reasons: 1) the variable consumes memory and 2) the return helps short circuit code which may not need to need to be run. As I don't generally mix assembler with C, I'm not the best one to fix your particular code. In fact, the compilers I use all have functions and/or defs built in to do this, so you can just go directly after the bit value without resorting to writing your own function. That is, in say MikroC you say something like: PORTA=0x00; TRISA=0x00; if (PORTA.F1) { //do stuff here } Each C compiler has a little different way of doing this (like CCS C has functions, etc), but the idea is the same. Back on the return thing, what I am talking about would be something like: char yourfunction(char arg) { if (PORTA.F1) return 1; return 0; }

Hi Vitaliy, Actually - Turbo Pascal, then D4 then D5 and now BDS2006 Love Delphi, just detest Borland or Code Gear as they call themselves these days. Delphi rocks big time 8-) but alas its is time to learn C. Have been putting it of for years Kind Regards Grant Brown Vitaliy wrote: {Quote hidden}> Grant Brown wrote: > >> Not much in C but 20 odd years in Delphi. >> > > Surely, you must mean 'Pascal'. Delphi is only 13 years old: > > http://en.wikipedia.org/wiki/CodeGear_Delphi#History > > I'm also a hard-core Delphi fan -- alas, it may be fair to say, a "former > fan"... > > Vitaliy > > -- Kind Regards Grant Brown SiteDoc Pty Ltd mob: 0412 926 995 http://www.sitedoc.com.au __________________________________________________________________________________________________________ This email message together with any attachments is intended only for the addressee(s) and contains information that may be confidential and/or copyright. If you are not the intended recipient, please notify the sender by reply email (or telephone SiteDoc Pty Ltd on +61 2 42291185) and immediately delete this email together with any attachments from your computer. If you are the intended recipient, you must not copy, disclose, reproduce or distribute this communication together with any attachments without the authority of SiteDoc Proprietary Limited. No representation is made that this email or any attachments are free of viruses. Virus scanning is recommended and is the responsibility of the recipient. Unless specifically stated by the sender as the views of SiteDoc Proprietary Limited, any views expressed in this message are those of the individual sender, and no responsibility will be borne by SiteDoc Proprietary Limited for its content or outcomes.

Hi Forrest, That was one of the best explanations I think if have read in a long time, wish all post where as good as that - including mine. char yourfunction(char arg) { if (PORTA.F1) return 1; return 0; } That was what I was trying to achieve but I had the "Return 0" in the wrong place. Now that I understand that return is really an exit command it makes sense. Learning C on a PIC may be somewhat hard but I intend to conquer it and I will - one just has to be very stubborn and not let it bet ya. The PIC that my actual project will be completed with is a PIC32 which seems to be a little bit more user friendly. But I need to get the basics down pat first. Many thanks for your assistance, very much appreciated. Kind regards Grant Brown Forrest W Christian wrote: {Quote hidden}> Grant Brown wrote: > >> Not much in C but 20 odd years in Delphi. >> >> > You may want to look at mikropascal then... > http://www.mikroe.com/en/compilers/mikropascal/pic/ . I'm not trying > to discourage you from learning C... but learning C on a PIC should be > an interesting experience.... > > One thing you need to keep in mind is that a PIC is EXTREMELY resource > limited, and there are things you would normally do which will fail > miserably on a PIC, just because of lack of code and or data space - > even though the compiler is perfectly happy to let you try. > >> I think I was confusing "return" with "Result" in Delphi which does act >> as a temporary variable until the function exits. >> >> > Yep... That's why I caught the not a lot of C.... Anyone who's > written much C would have caught this mistake :) ... But again, I've > put a few semicolons in the wrong spot and couldn't figure out why it > was always executing a block (or not). > >> so for the given function below is the way I have re-written it correct >> - so in other words do I just >> >> * declare a local variable >> * assign it a value >> * then return the local variable >> >> > For programming efficiency, I'd recommend using an early return instead > of a scratch variable. There are two reasons: 1) the variable consumes > memory and 2) the return helps short circuit code which may not need to > need to be run. As I don't generally mix assembler with C, I'm not the > best one to fix your particular code. In fact, the compilers I use all > have functions and/or defs built in to do this, so you can just go > directly after the bit value without resorting to writing your own > function. That is, in say MikroC you say something like: > > PORTA=0x00; > TRISA=0x00; > > if (PORTA.F1) > { > //do stuff here > } > > Each C compiler has a little different way of doing this (like CCS C has > functions, etc), but the idea is the same. > > Back on the return thing, what I am talking about would be something like: > > char yourfunction(char arg) > { > if (PORTA.F1) return 1; > return 0; > } > > > -- Kind Regards Grant Brown SiteDoc Pty Ltd mob: 0412 926 995 http://www.sitedoc.com.au __________________________________________________________________________________________________________ This email message together with any attachments is intended only for the addressee(s) and contains information that may be confidential and/or copyright. If you are not the intended recipient, please notify the sender by reply email (or telephone SiteDoc Pty Ltd on +61 2 42291185) and immediately delete this email together with any attachments from your computer. If you are the intended recipient, you must not copy, disclose, reproduce or distribute this communication together with any attachments without the authority of SiteDoc Proprietary Limited. No representation is made that this email or any attachments are free of viruses. Virus scanning is recommended and is the responsibility of the recipient. Unless specifically stated by the sender as the views of SiteDoc Proprietary Limited, any views expressed in this message are those of the individual sender, and no responsibility will be borne by SiteDoc Proprietary Limited for its content or outcomes.

> -----Original Message----- > From: spam_OUTpiclist-bouncesTakeThisOuTmit.edu [.....piclist-bouncesKILLspam@spam@mit.edu] On Behalf {Quote hidden}> Of Grant Brown > Sent: 09 September 2008 07:24 > To: Microcontroller discussion list - Public. > Subject: Re: [PIC] Reading an input > > Hi Bob, > > Thanks for that, > > Just to add to my learning why does it always return 0 ? > > I thought the idea with BTFSS was that it skipped the next instruction > only if the bit was not set ie 0 > > Does return not act as a temporary variable until the function exits ? I'm wondering if you are used to Visual Basic as you can use the function name to hold a temporary value like this until you exit the function. Return in C is equivalent to either return (if no value to return to caller) or retlw (to return a value to the caller) in PIC assembler. Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. =======================================================================

Grant Brown wrote: > char ReadPort_A_Bit(unsigned int BitReq) > { > return 0; > #asm > BANKSEL PORTA; // select bnak for port A > BTFSS PORTA BitReq; // read the bit value > return 1; > #endasm > } > > But it does not seem to be working so could someone point me in the > right direction. This is exactly the kind of trouble you will continue to get yourself into until you really understand the PIC. You are having a problem because you are using C before you are ready to do so. As was said before by several people: Learn the PIC with assembler first. No, I'm not going to provide new advice since you are ignoring previous advice. ******************************************************************** Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products (978) 742-9014. Gold level PIC consultants since 2000.

There is a book by Nigel Gardener of Bluebird Electronics (possibly available still from Farnell) entitled 'An introduction to programming the Microchip Pic in C " (which ought to get a prize purely for the length of the title), whcih you might find useful as it has example assembler produced by (I think the CCS compiler) along with the 'C' code that provided it. An alternative guide (FREE) to 'C' and Piccing can be downloaded from http://www.fored.co.uk, thoughI have to say, it isn't as clear as it could be. There is also example code that can be purchased (again for CCS I think) from http://www.phanderson.com - this will be examples from his Morgon State University engineering courses. Oh yes the Nigel Gardener book - ISBN 1-899013-04-0 Colin -- cdb, colinKILLspambtech-online.co.uk on 9/09/2008 Web presence: http://www.btech-online.co.uk Hosted by: http://www.1and1.co.uk/?k_id=7988359

On Tue, Sep 9, 2008 at 7:15 PM, Grant Brown <.....grantKILLspam.....sitedoc.com.au> wrote: > Learning C on a PIC may be somewhat hard but I intend to conquer it and > I will - one just has to be very stubborn and not let it bet ya. > > The PIC that my actual project will be completed with is a PIC32 which > seems to be a little bit more user friendly. But I need to get the > basics down pat first. If you are going to use PIC32, maybe you can forget about the mid-range PIC. They are so different. Since you are an IT professional and proficient in Delphi, learning C should not be a problem for you. However, you may want to learn some basics of Electronics and basic Microcontroller. And you can start right away from PIC32 if you get the demo board. If you want to use DIP package, maybe you can start with PIC24 even though it is also quite different from PIC32. At least the C compiler used for PIC24 and PIC32 have much in common (both are based on GCC). Anyway, to start with any PICs, you need to understand the datasheets. To understand the datasheet, you need to know a bit of assembly. And you need the hardware as well. Xiaofan

Olin Lathrop wrote: > Grant Brown wrote: > >> <snip> >> >> But it does not seem to be working so could someone point me in the >> right direction. >> > > This is exactly the kind of trouble you will continue to get yourself into > until you really understand the PIC. You are having a problem because you > are using C before you are ready to do so. > > <snip> > I second Olin's advice as I am learning C on the PIC's as we speak. I learned to use assembly on each PIC that I have used in a project. That includes understanding how peripherals function as well as how to configure them. This approach has really helped get over some hurdles in C because I can look at the assembly language result of compiling C source and understand what is happening when my C code fails. Last week at the library I found what I feel is a good book on C for the absolute beginner (me!). "C In Plain English" by Brian Overland ISBN 1-55828-430-3 This book has explained many things I could not wrap my head around. Just a suggestion that may help -- Regards, Stephen D. Barnes

On Sep 9, 2008, at 6:10 AM, Xiaofan Chen wrote: >> Learning C on a PIC may be somewhat hard but I intend to conquer it >> and >> I will - one just has to be very stubborn and not let it bet ya. > > to start with any PICs, you need to understand the > datasheets. To understand the datasheet, you need to know > a bit of assembly. And you need the hardware as well. Hmm. On the CPUs where it's not intended for you to ever program in anything but C, the datasheets talk C, and the manufacturer probably supplies a STANDARD C library for manipulating the hardware. And the datasheets pretty much SUCK for describing how the HW works at the bit level. I first ran into this on the Luminary Micro Cortex M3 CPUs; they provide a very complete C library for doing things, and thats apparently how they expected you to do things, because the datasheet sure didn't describe anything well enough to write your own assembly from scratch. I found it very frustrating, actually... So the problem with programming a PIC in C is that there isn't any STANDARD C library for manipulating the hardware (and it doesn't help that there's SO many different HW variants.) Each compiler has some libraries, but they're at different levels of functionality... BillW

On Wed, Sep 10, 2008 at 10:21 PM, William Chops Westfield <EraseMEwestfwspam_OUTTakeThisOuTmac.com> wrote: > I first ran into this on the Luminary Micro Cortex M3 CPUs; they > provide a very complete C library for doing things, and thats > apparently how they expected you to do things, because the datasheet > sure didn't describe anything well enough to write your own assembly > from scratch. I found it very frustrating, actually... Hmm, I believe for ARM based MCUs, they expect you to program in C. However it is still possible to program in ASM. They expect you to read the Core manuals from ARM then, so the datasheet does not touch too much on the core. > So the problem with programming a PIC in C is that there isn't any > STANDARD C library for manipulating the hardware (and it doesn't help > that there's SO many different HW variants.) Each compiler has some > libraries, but they're at different levels of functionality... > It is said Microchip provides "demo" quality peripheral library for MPLAB C18. Once upon a time they even intend to discontinue the library by saying that "From the release of MPLAB C18 v2.42 onward, no support has been added to the peripheral libraries". Apparently a lot of people's complains make them to continue it but the quality is still questionable. Xiaofan

On Thu, Sep 11, 2008 at 7:17 AM, Xiaofan Chen <xiaofancspam_OUTgmail.com> wrote: >> So the problem with programming a PIC in C is that there isn't any >> STANDARD C library for manipulating the hardware (and it doesn't help >> that there's SO many different HW variants.) Each compiler has some >> libraries, but they're at different levels of functionality... >> > > It is said Microchip provides "demo" quality peripheral library for MPLAB > C18. Once upon a time they even intend to discontinue the library by > saying that "From the release of MPLAB C18 v2.42 onward, no support has > been added to the peripheral libraries". Apparently a lot of people's > complains make them to continue it but the quality is still questionable. > The reference is here: http://forum.microchip.com/tm.aspx?m=282340 Xiaofan