Post by thread:[PIC]: floating point headaches

Hello all: I haven't been messing around with pics for a while....but just picked it back up again a couple of weeks ago and forgot how much fun it was. Now, onto the plea for help.... I admit...I've ALWAYS been scared of floating point routines, but the time has come where I MUST use them....the Microchip routines scare me worse than any of them....but maybe I'm just being stupid and ignorant of binary math...in any case...I've found these routines which look good to me and I think I can use. What I'm trying to do is multiply the 10-bit A/D value that I obtained from my F876 by 0.0048828125 to get the resultant voltage...the only thing I don't know how to do is get the A/D value (an integer) into floating point notation, actually, I guess I don't know how to get the 0.0048828 value into floating point notation either, but that's just a constant...how would I convert an integer to a float? the float routines that I'm using use two 16-bit arguments with an 8-bit mantissa and an extra sign byte (which I don't know what does yet) here's one of the routines (some call statements may be missing...I just gave a snippit): ;******************************************************************* ; Binary Floating Point Multiplication : ; ACCb(16 bits)EXP(b) * ACCa(16 bits)EXPa -> ACCb(16 bits)EXPb F_mpy: call S_SIGN call setup mloop: bcf STATUS,C ; clear carry bit ?????????? rrf ACCdHI,F ;rotate d right rrf ACCdLO,F btfsc STATUS,C ;need to add? call D_add rrf ACCbHI,F rrf ACCbLO,F rrf ACCcHI,F rrf ACCcLO,F decfsz temp, F ;loop until all bits checked goto mloop movf EXPa,W addwf EXPb, F IF Mode16 movf ACCbHI, F btfss STATUS,Z goto finup ; if ACCbHI != 0 movf ACCbLO, F btfss STATUS,Z goto Shft08 ; if ACCbLO != 0 && ACCbHI == 0 movf ACCcHI,W movwf ACCbHI ; if ACCb == 0, then move ACCc to ACCb movf ACCcLO,W movwf ACCbLO movlw .16 addwf EXPb, F goto finup Shft08: movf ACCbLO,W movwf ACCbHI movf ACCcHI,W movwf ACCbLO movlw .8 addwf EXPb,F ENDIF ; matching endif for IF Mode16 finup: btfss sign,MSB goto F_norm decf ACCcLO,F ; negate ACCc comf ACCcLO,F btfsc STATUS,Z decf ACCcHI,F comf ACCcHI,F btfsc STATUS,Z neg_B: decf ACCbLO,F ; negate ACCb comf ACCbLO,F btfsc STATUS,Z decf ACCbHI,F comf ACCbHI,F goto F_norm thanks for your time! -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

{Quote hidden}> Hello all: > > I haven't been messing around with pics for a while....but just > picked it back up again a couple of weeks ago and forgot how much fun it > was. > Now, onto the plea for help.... > > I admit...I've ALWAYS been scared of floating point routines, but > the time has come where I MUST use them....the Microchip routines scare > me worse than any of them....but maybe I'm just being stupid and > ignorant of binary math...in any case...I've found these routines which > look good to me and I think I can use. What I'm trying to do is > multiply the 10-bit A/D value that I obtained from my F876 by > 0.0048828125 to get the resultant voltage...the only thing I don't know > how to do is get the A/D value (an integer) into floating point > notation, actually, I guess I don't know how to get the 0.0048828 value > into floating point notation either, but that's just a constant...how > would I convert an integer to a float? the float routines that I'm > using use two 16-bit arguments with an 8-bit mantissa and an extra sign > byte (which I don't know what does yet) here's one of the routines (some > call statements may be missing...I just gave a snippit): You don't necessarily have to go to floating point. There may be a couple of alternatives using 16 bit integer maths:- 1) 10 bit A/D result is a count of 1023. Scale your analog input by resistor divider slightly to give a max count of 1000. Multiply by integer 5, you get a 16 bit result 0-50000 that represents an input of 0-5V. Put in the decimal point where it needs to be when printing out or displaying. Even if you don't scale and just ignore any ADC count over 1000 the error is only about 2%. 2) Multiply by a fraction (multiply then divide). Eg: x18/37 gives a max of 497 which could read 4.97 volts. Or x40/82 = 499, or even better x45/92 = 500. All this fits in 16 bits OK. Brent Brown Electronic Design Solutions 16 English Street Hamilton, New Zealand Ph/fax: +64 7 849 0069 Mobile/text: 025 334 069 eMail: spam_OUTbrent.brownTakeThisOuTclear.net.nz -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

At 04:48 PM 6/26/01 -0700, you wrote: > I admit...I've ALWAYS been scared of floating point routines, but >the time has come where I MUST use them.... And why would that be? It's very seldom actually necessary, you know. Just scale and use 16, 24 or even 32 bit fixed point math (possibly adjusting the scaling with shifts between operations). > the Microchip routines scare >me worse than any of them....but maybe I'm just being stupid and >ignorant of binary math...in any case...I've found these routines which >look good to me and I think I can use. What I'm trying to do is >multiply the 10-bit A/D value that I obtained from my F876 by >0.0048828125 to get the resultant voltage...the only thing I don't know >how to do is get the A/D value (an integer) into floating point >notation, actually, I guess I don't know how to get the 0.0048828 value >into floating point notation either, but that's just a constant...how Is there not a routine for doing the conversion in the package? The only complex thing is that you should normalize the number, which means that it effectively is left shifted and the exponent decremented until the leftmost bit is a one (often an implied "one", depending on the format), except for the special case of a zero. In the case of Microchip's format, the implied "1" is replaced by the sign bit. The exponent is like the base 10 exponent you are used to, except it is base 2, and except it is "biased" by -127 so the routines don't have to do signed math. Neither is anything to be scared of. BTW, one of the piclist members has written a conversion applet, called floatconv.exe Best regards, =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Spehro Pefhany --"it's the network..." "The Journey is the reward" .....speffKILLspam@spam@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> the float routines that I'm > using use two 16-bit arguments with an 8-bit mantissa and an extra sign > byte 8 bit mantissa isn't enough if you want to make full use of the 10 bit A/D results. I use a 24 bit format for this kind of stuff. It includes 1 sign bit, 7 exponent bits, and 16 mantissa bits with an implied vestigual 1 bit. ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, olinKILLspamembedinc.com, http://www.embedinc.com -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Spehro Pefhany wrote : > Neither is anything to be scared of. BTW, one of the piclist members > has written a conversion applet, called floatconv.exe With floatconv.exe : In Microchip 24bit mode some conversions are slightly incorrect eg: 22702080 into the Float textbox and Convert to Byte Microchip 32 bit: 972D3400 (ok) Microchip 24 bit : 972D34 (ok) 22702079 into the Float textbox and Convert to Byte Microchip 32 bit: 972D33FE (ok) Microchip 24 bit : 972D32 (not ok - it is too low) However its very useful and I use it often, but only in 32 bit mode. James -- 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

Sorry, I MEANT to say 16 bit mantissa with an 8-bit exponent.... Jonathan Olin Lathrop wrote: {Quote hidden}> > the float routines that I'm > > using use two 16-bit arguments with an 8-bit mantissa and an extra sign > > byte > > 8 bit mantissa isn't enough if you want to make full use of the 10 bit A/D > results. I use a 24 bit format for this kind of stuff. It includes 1 sign > bit, 7 exponent bits, and 16 mantissa bits with an implied vestigual 1 bit. > > ******************************************************************** > Olin Lathrop, embedded systems consultant in Littleton Massachusetts > (978) 742-9014, EraseMEolinspam_OUTTakeThisOuTembedinc.com, http://www.embedinc.com > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- 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

Alright, I worked on it a few hours and got it...without floating point......as it turns out I didn't need to use voltage at all....I'm trying to use an AD22100 temperature chip. It has a 0 degree level of 1.375V so I simply (1) took that 10 bit number in A/D steps (~282) subtracted it from the A/D value present on an0 then divided by the chip's temp coefficient 0.0225, but what I actually did was multiply step (1) by: 1 5V ----------- x------------ = 217 (without decimal place) and then just placed the decimal point where it was appropriate 0.0225 V/C 1024 thanks for your all your help! Jonathan Jonathan Newport wrote: {Quote hidden}> Hello all: > > I haven't been messing around with pics for a while....but just > picked it back up again a couple of weeks ago and forgot how much fun it > was. > Now, onto the plea for help.... > > I admit...I've ALWAYS been scared of floating point routines, but > the time has come where I MUST use them....the Microchip routines scare > me worse than any of them....but maybe I'm just being stupid and > ignorant of binary math...in any case...I've found these routines which > look good to me and I think I can use. What I'm trying to do is > multiply the 10-bit A/D value that I obtained from my F876 by > 0.0048828125 to get the resultant voltage...the only thing I don't know > how to do is get the A/D value (an integer) into floating point > notation, actually, I guess I don't know how to get the 0.0048828 value > into floating point notation either, but that's just a constant...how > would I convert an integer to a float? the float routines that I'm > using use two 16-bit arguments with an 8-bit mantissa and an extra sign > byte (which I don't know what does yet) here's one of the routines (some > call statements may be missing...I just gave a snippit): > > ;******************************************************************* > ; Binary Floating Point Multiplication : > ; ACCb(16 bits)EXP(b) * ACCa(16 bits)EXPa -> ACCb(16 bits)EXPb > > F_mpy: call S_SIGN > call setup > mloop: bcf STATUS,C ; clear carry bit ?????????? > rrf ACCdHI,F ;rotate d right > rrf ACCdLO,F > btfsc STATUS,C ;need to add? > call D_add > rrf ACCbHI,F > rrf ACCbLO,F > rrf ACCcHI,F > rrf ACCcLO,F > decfsz temp, F ;loop until all bits checked > goto mloop > > movf EXPa,W > addwf EXPb, F > > IF Mode16 > movf ACCbHI, F > btfss STATUS,Z > goto finup ; if ACCbHI != 0 > movf ACCbLO, F > btfss STATUS,Z > goto Shft08 ; if ACCbLO != 0 && ACCbHI == 0 > > movf ACCcHI,W > movwf ACCbHI ; if ACCb == 0, then move ACCc to ACCb > movf ACCcLO,W > movwf ACCbLO > movlw .16 > addwf EXPb, F > goto finup > > Shft08: movf ACCbLO,W > movwf ACCbHI > movf ACCcHI,W > movwf ACCbLO > movlw .8 > addwf EXPb,F > > ENDIF ; matching endif for IF Mode16 > > finup: btfss sign,MSB > goto F_norm > > decf ACCcLO,F ; negate ACCc > comf ACCcLO,F > btfsc STATUS,Z > decf ACCcHI,F > comf ACCcHI,F > btfsc STATUS,Z > > neg_B: decf ACCbLO,F ; negate ACCb > comf ACCbLO,F > btfsc STATUS,Z > decf ACCbHI,F > comf ACCbHI,F > > goto F_norm > > thanks for your time! > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- 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