Using a RAM structure as a byte array

[drawbars]

Hi All,

This is probably old hat to some of you, and while I've done it 1,000x in Assembler, I'm unsure of how to go about it in PICC ...

I have a project where I occasionally need to send system status out a serial interface. The data in the status is NOT all the same size, so an array doesn't eliminate my problems:

int16 variable1;
int8 variable2;
int8 variable3;
int8 variable4;
int32 variable5;


I want to be able to access them as individual variables of varying sizes, AND I want to be able to use a pointer to variable1 to send the whole mess out a serial port, in one gulp, high-endian, without having to worry about the byte sizes. This is not a bulk backup to storage; byte order matters at the other end.

The question that I have is, since PICC handles all of the RAM management behind the scenes, how can I guarantee that these five variables will occupy 9 continguous locations in the compiled program? Will a structure alone guarantee this? (The manual and help file aren't much ... er, help on this matter.)

And when I go to set a pointer to the collection, can I just typecast a byte pointer to variable1, and they'll all come out in order? Or am I asking for byte-swapping, invalid data, etc.? The only 100% safe way that I can think of is to define a structure, then create a union with an array of 9 bytes. That seems ludicrous, given that the result is in the form of a.b->c -- C is supposed to be EASIER than Assembler, not harder! Any thoughts?

TIA,

-BW

[PCM programmer]

[treitmey]

PCM is right. For me I take care of this at PC side
((since it has the horsepower))

To simply send them out in consecutive bytes, you can use a array,,... a struct in your case since they change in size.

Then you can have a ponter to the struct and get all the fun . -> stuff
and a pointer to the buffer you want to send.
take a look at modbus packt struct modbus
http://www.ccsinfo.com/forum/viewtopic.php?t=19306&highlight=modbus

[drawbars]

Hi PCM,

Thanks. It looks like a struct is all I need to keep the bytes in line.

And while I said "high-endian," I meant low-endian (the other high-endian! ), so that should work out OK, too.


Regards,

-BW
Bruce Wahler
Design Consultant
Ashby Solutions™
http://consult.ashbysolutions.com