Post by thread:Moving to C

Hi, I have finally succumbed and decided to start using C on PIC projects. I have some limited C knowledge (writing windows DLLs in order to make VB3 maths run faster and a bit of code maintenance), but nothing related to using C for embedded applications or small processors. In an up-comimg project, I have a requirement to count the number of pulses on an input pin. The pulses will be about 100us wide and can come in with periods from 5ms to several days between them. If I were writing this in assembler I may code the pulse detection part something like: ( assume pulses are on RA0 ) wait4lo btfsc Port_A, 0 goto wait4lo goto $+1 ; add some de-glitching goto $+1 btfsc Port_A, 0 goto wait4lo wait4hi btfss Port_A, 0 goto wait4hi goto $+1 ; add some de-glitching goto $+1 btfss Port_A, 0 goto wait4hi ... do the counting and any other stuff here ... goto wait4lo How would something like this be coded in C? Regards, Mike Watson

On Tue, Oct 14, 1997 at 01:09:29PM +0000, Mike Watson wrote: > I have finally succumbed and decided to start using C on PIC projects. ... > In an up-comimg project, I have a requirement to count the number of > pulses on an input pin. The pulses will be about 100us wide and can > come in with periods from 5ms to several days between them. ... > How would something like this be coded in C? Pretty much the same as in assembler. Like this (tweak the DELAY counts to ensure reliable detection with noise rejection): #include <pic.h> static volatile bit PulseIn @ (unsigned)&PORTA*8+0; // bit0 in port A static unsigned int pulsecount; // pulse accumulator #define DELAY(n) {unsigned char i = n ; do ; while(--i);} main() { for(;;) { // wait for a verified low level on the input while(PulseIn == 1) continue; DELAY(5); // wait a bit (or 5) if(PulseIn == 1) continue; // just noise - ignore it // wait for a verified high level on the input for(;;) { while(PulseIn == 0) continue; DELAY(5); // wait a bit (or 5) if(PulseIn == 1) break; // not just noise - it's ok } pulsecount++; // increment count or whatever } } -- Clyde Smith-Stubbs | HI-TECH Software Email: spam_OUTclydeTakeThisOuThtsoft.com | Phone Fax WWW: http://www.htsoft.com/ | USA: (408) 490 2885 (408) 490 2885 PGP: finger .....clydeKILLspam@spam@htsoft.com | AUS: +61 7 3354 2411 +61 7 3354 2422 --------------------------------------------------------------------------- ANSI C for the PIC! Now shipping! See http://www.htsoft.com for more info.

Anyone have any new information about when the Scenix SX devkit will be available from Parallax? I see that Scenix posted an incomplete data sheet, but nothing else new. Also, I heard the SX will be able to read its own program memory during execution, which is supposed to aid in lookups and table branching. Is this true? Thanks Steve

Mike Watson wrote: > Hi, > > I have finally succumbed and decided to start using C on PIC projects. > > How would something like this be coded in C? > > Regards, > > Mike Watson And while we are at it would some one explain how to go about creating and reading a lookup table? Please? Rwetty pwease? -- Eric van Es | Cape Town, South Africa vanesKILLspamilink.nis.za | http://www.nis.za/~vanes LOOKING FOR TEMPORARY / HOLIDAY ACCOMODATION? http://www.nis.za/~vanes/accom.htm

On Wed, Oct 15, 1997 at 12:17:40AM +0200, Eric van Es wrote: > And while we are at it would some one explain how to go about creating and > reading a lookup table? Sure, but what kind of lookup table? When programming a PIC in assembler, a "lookup table" usually refers to a retlw table that is necessary to use ROM for storing any kind of data - when using a C compiler this will get done for you, e.g. the following array is used in a 7 segment display routine to translate digits into 7 segment patterns; you don't have to worry about how to implement it - the compiler does it. static const unsigned char digits[10] = { 0x5F, /* 0 */ 0x06, 0x3B, 0x2F, /* 3 */ 0x66, 0x6D, 0x7D, 0x07, /* 7 */ 0x7F, 0x6F, }; Using this later - segcnt is a segment mask: PORTB |= segcnt & digits[curval % 10]; -- Clyde Smith-Stubbs | HI-TECH Software Email: .....clydeKILLspam.....htsoft.com | Phone Fax WWW: http://www.htsoft.com/ | USA: (408) 490 2885 (408) 490 2885 PGP: finger EraseMEclydespam_OUTTakeThisOuThtsoft.com | AUS: +61 7 3354 2411 +61 7 3354 2422 --------------------------------------------------------------------------- ANSI C for the PIC! Now shipping! See http://www.htsoft.com for more info.

On Wed, Oct 15, 1997 at 12:17:40AM +0200, Eric van Es wrote: > And while we are at it would some one explain how to go about creating and > reading a lookup table? Sure, but what kind of lookup table? When programming a PIC in assembler, a "lookup table" usually refers to a retlw table that is necessary to use ROM for storing any kind of data - when using a C compiler this will get done for you, e.g. the following array is used in a 7 segment display routine to translate digits into 7 segment patterns; you don't have to worry about how to implement it - the compiler does it. static const unsigned char digits[10] = { 0x5F, /* 0 */ 0x06, 0x3B, 0x2F, /* 3 */ 0x66, 0x6D, 0x7D, 0x07, /* 7 */ 0x7F, 0x6F, }; Using this later - segcnt is a segment mask: PORTB |= segcnt & digits[curval % 10]; -- Clyde Smith-Stubbs | HI-TECH Software Email: clydespam_OUThtsoft.com | Phone Fax WWW: http://www.htsoft.com/ | USA: (408) 490 2885 (408) 490 2885 PGP: finger @spam@clydeKILLspamhtsoft.com | AUS: +61 7 3354 2411 +61 7 3354 2422 --------------------------------------------------------------------------- ANSI C for the PIC! Now shipping! See http://www.htsoft.com for more info.