Post by thread:R: Re: questions

-----Messaggio originale----- Da: Clyde Smith-Stubbs <spam_OUTclydeTakeThisOuTHTSOFT.COM> A: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU <PICLISTKILLspamMITVMA.MIT.EDU> Data: sabato 6 maggio 2000 3.35 Oggetto: Re: questions >On Sat, May 06, 2000 at 02:02:58AM +0200, Massimiliano Dellisanti Vilardi wrote: >> - Is there a way to compile a c source where there are unsigned long variable? How can I solve this problem? How can I use 32 bit integers? Can I solve this problem with the new C18 compiler? > >Yes, get HI-TECH C. It supports all ANSI data types. > Is it possible to get an evaluation version? Does it work with PIC17C766 ? >> - Is there another way to reset a bit? I mean is there a better C code than this : PORTX &= (0xFF - mybit) ?? > >Like this: > > PORTX &= ~mybit; > >This assumes that "mybit" is a byte-size thing, and you want to reset the >corresponding bits. The ~ operator is a bitwise inversion. To reset a single bit, use > > PORTX &= ~(1 << bitno); > >A decent compiler will optimize this when bitno is a constant to a single instruction. > ...but what happens if some lines of PORTX are configured as Output? The statement (PORTX &= something) means that PORTX must be read and then written: what happens when I read output lines? I thought there was a way to access directly a bit: I guess this is possible using assembly: isn't there a way to do it in C ? Thank you for your answer. Max

> Is it possible to get an evaluation version? Does it work with PIC17C766 ? Yes it does work with the 17C766. There is a demo version on our web site, but this does not have the 17Cxx support. We can arrange an evaluation of the full compiler - contact .....salesKILLspam.....htsoft.com for more information. > ...but what happens if some lines of PORTX are configured as Output? The > statement (PORTX &= something) means that PORTX must be read and then > written: > what happens when I read output lines? The same thing that happens when you read them in assembler. > I thought there was a way to access directly a bit: I guess this is possible > using assembly: isn't there a way to do it in C ? The above C code *will* produce a single bit instruction, but just as in assembler, this still results in a read/modify/write cycle on the port. Whether you use assembler or C, you must deal with this if required, by keeping a shadow copy of the output data. This is required only if a) you intend switching bits in the port between input and output, or b) if an output pin could be driven high or low by external logic. If your hardware is properly designed this will only occur if you use an open-drain output. But remember, this is not a C or assembler issue, this is a hardware issue. Regards, Clyde -- Clyde Smith-Stubbs | HI-TECH Software Email: EraseMEclydespam_OUTTakeThisOuThtsoft.com | Phone Fax WWW: http://www.htsoft.com/ | USA: (408) 490 2885 (408) 490 2885 PGP: finger clydespam_OUThtsoft.com | AUS: +61 7 3355 8333 +61 7 3355 8334 --------------------------------------------------------------------------- HI-TECH C: compiling the real world.