Post by thread:Re: Subroutine locations

Tim Crist <spam_OUTPICLISTTakeThisOuTMITVMA.MIT.EDU> wrote: > I have a question about subroutines that are located above and > below 255H in the 16F84 and the 16C54A. Tim: I think you mean "0FFH", or "255 decimal". > My question is: Can I have a subroutine below 255H successfully > call a subroutine above 255H without incident? On the 16F84, it'll work just fine; subroutines can be anywhere in the memory space and can be called from anywhere else without any special effort. On the 16C54, it's a different story... All subroutine entry-points must be located in the first half of memory, between 000H and 0FFH. -Andy === Andrew Warren - .....fastfwdKILLspam@spam@ix.netcom.com === Fast Forward Engineering - Vista, California === http://www.geocities.com/SiliconValley/2499

> Van: Tim Crist <tjcristKILLspamCCGATE.HAC.COM> > Aan: .....PICLISTKILLspam.....MITVMA.MIT.EDU > Onderwerp: Subroutine locations > Datum: maandag 30 maart 1998 13:29 > > I have a question about subroutines that are located above and > below 255H in the 16F84 and the 16C54A. I understand that tables > that use the program counter will not work if they cross 255H > because of PCLATH. I assume you mean 255 Decimal (or FF HexaDecimal). You are right, but for the wrong reasons. It's not because of PCLATH, but because the register PCL consists outof only 8 bits. this means that you can't put a number higher than FF (or 255 decimal) into PCL. Said otherwise, if you add a Index of 0x05 to a PCL of 0xFE the result will become 0x03, and NOT 0x0103. Ah. before I forget : The low 5 bits of PCLATH will be prepended to PCL to obtain the full 13 -bit adres on a add-to-PCL -jump. Not that all PIC's have that much Code-memory, but it seems to be a sort of standard for Mid-range PIC's. > My question is: Can I have a subroutine below 255H successfully > call a subroutine above 255H without incident? If not, how would > one go about making it work. Yes, they can. A Goto or Call has a 11 Bit adres, wich means you can jump from 0x0000 to 0x07FF. If you would like to be able to jump to an adres beyond this, you would have to (besides finding a PIC with more Code-memory) set bits 3 & 4 in the PCLATH register. these will be prepended to your Jump/ Call adres to obtain (again) the full 13 -bit adres. > TIA, > > Tim Crist Greetz, Rudy Wieser

unsubscribe remove quit {Quote hidden}> -----Original Message----- > From: pic microcontroller discussion list > [EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU]On Behalf Of Caisson > Sent: Tuesday, March 31, 1998 3:38 AM > To: PICLISTspam_OUTMITVMA.MIT.EDU > Subject: Re: Subroutine locations > > > > Van: Tim Crist <@spam@tjcristKILLspamCCGATE.HAC.COM> > > Aan: KILLspamPICLISTKILLspamMITVMA.MIT.EDU > > Onderwerp: Subroutine locations > > Datum: maandag 30 maart 1998 13:29 > > > > I have a question about subroutines that are located above and > > below 255H in the 16F84 and the 16C54A. I understand that tables > > that use the program counter will not work if they cross 255H > > because of PCLATH. > > I assume you mean 255 Decimal (or FF HexaDecimal). > > You are right, but for the wrong reasons. It's not because of PCLATH, but > because the register PCL consists outof only 8 bits. this means that you > can't put a number higher than FF (or 255 decimal) into PCL. Said > otherwise, > if you add a Index of 0x05 to a PCL of 0xFE the result will become 0x03, > and > NOT 0x0103. Ah. before I forget : The low 5 bits of PCLATH will be > prepended > to PCL to obtain the full 13 -bit adres on a add-to-PCL -jump. Not that > all > PIC's have that much Code-memory, but it seems to be a sort of > standard for > Mid-range PIC's. > > > My question is: Can I have a subroutine below 255H successfully > > call a subroutine above 255H without incident? If not, how would > > one go about making it work. > > Yes, they can. A Goto or Call has a 11 Bit adres, wich means you can jump > from 0x0000 to 0x07FF. If you would like to be able to jump to an adres > beyond this, you would have to (besides finding a PIC with more > Code-memory) > set bits 3 & 4 in the PCLATH register. these will be prepended to your > Jump/ > Call adres to obtain (again) the full 13 -bit adres. > > > TIA, > > > > Tim Crist > > Greetz, > Rudy Wieser >

---------- > Van: Syd Kahn <RemoveMEklassTakeThisOuTNETRAX.NET> > Aan: spamBeGonePICLISTspamBeGoneMITVMA.MIT.EDU > Onderwerp: Re: Subroutine locations > Datum: dinsdag 31 maart 1998 12:59 > > unsubscribe > remove > quit > [Cut] You may leave the list at any time by sending a "SIGNOFF PICLIST" command to TakeThisOuTLISTSERVEraseMEspam_OUTMITVMA.MIT.EDU (or RemoveMELISTSERVTakeThisOuTMITVMA.BITNET). Greetz, Rudy Wieser