Post by thread:[PIC]:treating CCPR1L and CCPR1H as an int in PICC

I am using HiTech PICC and want to subtract capture 1 from an integer value. I know there's a way to specify it in C so that it treats the sequential registers CCPR1L and CCPR1H as a 16 bit number, but can't put my finger on it. I know I could use a temporary integer but that would be wasteful and I could also do the subtraction in inline assembler but that isn't neccessary. I hate it when I can't remember how to do stuff like this. Thanks in advance, Bob Blick -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

>I am using HiTech PICC and want to subtract capture 1 from an integer >value. I know there's a way to specify it in C so that it treats the >sequential registers CCPR1L and CCPR1H as a 16 bit number, but can't put >my finger on it. Here's how I do TMR1 on a 16C77: static voltatile unsigned int TMR1 @0xFCE; -- ______________________________________ Andrew E. Kalman, Ph.D. spam_OUTaekTakeThisOuTpumpkininc.com -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> From: Bob Blick [.....bobKILLspam@spam@ted.net] > I am using HiTech PICC and want to subtract capture 1 from an integer > value. I know there's a way to specify it in C so that it treats the > sequential registers CCPR1L and CCPR1H as a 16 bit number, > but can't put > my finger on it. The function below uses a pointer and does what you want to do. I used 31415 for the subtraction just to have value. Be careful. 16 bit math is not atomic and CCPR1L and CCPR1H can change while you're working with them, if you're not configured correctly. -Mike int foobar(void) { int *foo; foo = &CCPR1L; return (31415 - (*foo)); } -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On Thu, 29 Mar 2001, Andrew E. Kalman wrote: > Here's how I do TMR1 on a 16C77: > > static volatile unsigned int TMR1 @0xFCE; Perfect. Thanks! -Bob -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

If it is anything like ANSI C the following should work (no guarantee on the efficiency of the generated code): return 31415 - * (int *) &CCPR1L To break it out, working right to left: &CCPR1L returns the address of CCPR1L, presumably an unsigned char (int *) says to treat that address as a pointer to an int instead of a pointer to an unsigned char * says to use the value pointed to be that pointer to an int Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) {Original Message removed}

Thanks for these good explanations! -Bob At 08:22 PM 3/29/2001 -0500, you wrote: {Quote hidden}>If it is anything like ANSI C the following should work (no guarantee on >the efficiency of the generated code): > > return 31415 - * (int *) &CCPR1L > >To break it out, working right to left: > >&CCPR1L returns the address of CCPR1L, presumably an unsigned char > >(int *) says to treat that address as a pointer to an int instead of a >pointer to an unsigned char > >* says to use the value pointed to be that pointer to an int > >Bob Ammerman >RAm Systems >(contract development of high performance, high function, low-level >software) > > >{Original Message removed}