Post by thread:LVP of 16f877 (RB3/PGM)

I do not know why Microchip would stick the Programming pin (RB3) in the middle of a port (RB0-RB7)... Why not Bit7 of a port so you would read/write 0x00-0x7F? Anyway, if RB3 ceases to be a GenPurpose I/O, when you read the port, what does the Bit3 read as (0 or 1)? Is the lower nibble Octal and the upper nibble Hex? If I use LPV, I am going to redefine RB4-RB7 as RB3-RB6 so I can read/write 0x00-0x7F. I will NOT call RB3/PGM this, I will refer it as PGM only. Hence, PortB will become a 7pin port. Less confusing. What do you think? -- Jason ======================================== Website: http://www.execpc.com/~milsumai E-Mail: spam_OUTmilsumaiTakeThisOuTexecpc.com ICQ # : 12978762 ======================================== .:::. ,,, _(- -)_ / ( ) \ \_/ : \_/ |_/ \_| | | | -TRY PRAYER-

Jason Muhammad wrote: > I do not know why Microchip would stick the Programming pin (RB3) in > the middle of a port (RB0-RB7)... Why not Bit7 of a port so you would > read/write 0x00-0x7F? ... > Less confusing. What do you think? I think it's a right foul-up! As I see it, LVP is basically un-usable and you need to use a 12V programmer and *always* disable it. Otrherwise regard PortB as a second PortA - incomplete, unsuitable for parallel byte-wise transfer. It appears to be a truly amazing extension of their design psychosis; like saying you shouldn't use OPTION and TRIS instructions which *are* still perfectly valid on this processor but won't work on the only truly byte-wide port remaining, where you probably most *NEED* to use TRIS! (Or will it?) -- Cheers, Paul B.

Yes, this amazed (and really annoyed me as a programmer designer and PIC program author). Scenix use the oscillator pins, surely Microchip could have come up with something using the OSC pins, MCLR and the existing programming pins ? Robin Abbott - .....robin.abbottKILLspam@spam@fored.co.uk ************************************************************************** * * Forest Electronic Developments * http://dspace.dial.pipex.com/robin.abbott/FED * ************************************************************************** {Original Message removed}

Paul (and Jason), without knowing the details of the process and the `floor plan' of the chip, I can only speculate. RB4..7 have additional logic for the interrupt-on-change feature as well as RB0 for external interrupts. RA has analog and timer inputs. RC has many functions and RD and RE are normally used for a standard parallel bus interface. I really wish they would have used RA5 but they would probably have to sacrifice an A/D channel and the slave-select input for the MSSP module. Obviously they had to trade something for the capability. It would be nice if they had moved LVP to one of the spare pins in the PLCC and QFP packages. - Tom At 07:58 AM 10/24/99 +1000, Paul B. Webster wrote: {Quote hidden}>Jason Muhammad wrote: > >> I do not know why Microchip would stick the Programming pin (RB3) in >> the middle of a port (RB0-RB7)... Why not Bit7 of a port so you would >> read/write 0x00-0x7F? >... >> Less confusing. What do you think? > > I think it's a right foul-up! As I see it, LVP is basically un-usable >and you need to use a 12V programmer and *always* disable it. > > Otrherwise regard PortB as a second PortA - incomplete, unsuitable for >parallel byte-wise transfer. > > It appears to be a truly amazing extension of their design psychosis; >like saying you shouldn't use OPTION and TRIS instructions which *are* >still perfectly valid on this processor but won't work on the only truly >byte-wide port remaining, where you probably most *NEED* to use TRIS! > > (Or will it?) ------------------------------------------------------------------------ Tom Handley New Age Communications Since '75 before "New Age" and no one around here is waiting for UFOs ;-)

> It appears to be a truly amazing extension of their design psychosis; >like saying you shouldn't use OPTION and TRIS instructions which *are* >still perfectly valid on this processor but won't work on the only truly >byte-wide port remaining, where you probably most *NEED* to use TRIS! > > (Or will it?) As far as I know, TRIS works only on ports 5,6,7 (A,B,C). So sad . . . I really would have preferred them to have used port A (its already incomplete - whats one more bit). dwayne Dwayne Reid <dwaynerKILLspamplanet.eon.net> Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 15 years of Engineering Innovation (1984 - 1999) * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Do NOT send unsolicited commercial email to this email address. My posting messages to Usenet neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email.