A couple of reasons.

1) Microchip has changed the names of certain registers and bit names=20
over the years.
2) Legacy code written before those names were changed will compile=20
cleanly and give the same results.

I do the same thing in my code: I'll include defines for each of the=20
different names that I've used over the years but changed along the way.

Note that your first example (RA & TRISA) are *not* the same=20
thing.  Yes - the definitions are the same but the registers are at=20
the same address in different RAM pages.

That said: I use exactly those same shortcuts in my code.  I simply=20
ensure that I am on the correct RAM page when doing so.

dwayne


At 11:59 AM 4/20/2015, Nathan House wrote:
>Hi,
>
>The main.pre file in my MPLAB X project seems to show the definitions for
>the configuration registers. One example is this:
>
>typedef union {
>struct {
>unsigned TRISA0 :1;
>unsigned TRISA1 :1;
>unsigned TRISA2 :1;
>unsigned TRISA3 :1;
>unsigned TRISA4 :1;
>unsigned TRISA5 :1;
>unsigned TRISA6 :1;
>unsigned TRISA7 :1;
>};
>struct {
>unsigned RA0 :1;
>unsigned RA1 :1;
>unsigned RA2 :1;
>unsigned RA3 :1;
>unsigned RA4 :1;
>unsigned RA5 :1;
>unsigned RA6 :1;
>unsigned RA7 :1;
>};
>} TRISAbits_t;
>extern volatile TRISAbits_t TRISAbits @ 0xF92;
>
>What is the point of making the same bits accessible through more than one
>name?
>
>I.e. the following lines of code are identical, correct?
>
>TRISAbits.RA0 =3D 1;
>TRISAbits.TRISA0 =3D 1;
>
>The LATAbits definition is even more convoluted:
>
>typedef union {
>struct {
>unsigned LATA0 :1;
>unsigned LATA1 :1;
>unsigned LATA2 :1;
>unsigned LATA3 :1;
>unsigned LATA4 :1;
>unsigned LATA5 :1;
>unsigned LATA6 :1;
>unsigned LATA7 :1;
>};
>struct {
>unsigned LA0 :1;
>};
>struct {
>unsigned :1;
>unsigned LA1 :1;
>};
>struct {
>unsigned :2;
>unsigned LA2 :1;
>};
>struct {
>unsigned :3;
>unsigned LA3 :1;
>};
>struct {
>unsigned :4;
>unsigned LA4 :1;
>};
>struct {
>unsigned :5;
>unsigned LA5 :1;
>};
>struct {
>unsigned :6;
>unsigned LA6 :1;
>};
>struct {
>unsigned :7;
>unsigned LA7 :1;
>};
>} LATAbits_t;
>extern volatile LATAbits_t LATAbits @ 0xF89;
>
>I don't know why they union'd a separate struct for each of the bits
>instead of putting them all in one struct like with TRISAbits, but the sam=
e
>question applies to this as well.
>
>What's the point of all that redundancy?
>
>Thanks,
>
>Nate
>
>-----
>
>I'm a college student, take it easy on me ;-)
>
>Check out my small hobby electronics business!
>www.foxytronics.com
>--
>http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>View/change your membership options at
>http://mailman.mit.edu/mailman/listinfo/piclist


--=20
Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax
www.trinity-electronics.com
Custom Electronics Design and Manufacturing

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