Re: [oopic] SCP, hexadecimal numbers, and byte swapping?

You nailed it. The PIC is "Little Endian" which means that it stores
data LSB first. Our PC's are "Big Endian" which is the other way around
and also the way we think and write. Sadly your only choice is to
simple do a byte swap AFTER you convert the binary number. One simple
way is to have a two byte array and fill it in reverse. You can use
math or simple bit shifts, but you'll just have to do it the obvious way.

DLC

Mike Smith wrote:
> Hi everyone -
>
> I am using SCP as a means for one OOPIC to read/write information to
> another OOPIC. Most of the values I'm interested in are two-byte
> oVar16 objects stored in variable memory, so my SCP command to
> retrieve a value looks something like:
>
> \1366J145HM
>
> (breaks down as Serial node1, Memory address 366, two-byte read)
>
> Assuming the variable object has the number 750 stored, this command
> returns:
>
> EE02m
>
> (two hexadecimal numbers EE and 02, followed by the "M" command
> confirmation of "m")
>
> I scratched my head for a little while trying to figure out how EE02
> in hexadecimal could equal the decimal number 750, but then realized
> that the bytes come through in last-byte-first order - (02EE does
> equal 750).
>
> Now I realize that if I were using oWord objects instead of oVar16's,
> I could use the default address of the object and get back a decimal
> string. However, by using oVar16's I get to use all that variable
> memory and conserve object memory for other things I need.
>
> I would like to know if anyone has suggestions for the most efficient
> way to take this "EE02m" value received from an oSerialPort object
> and properly convert so as to be used for displaying on an LCD(SET)?
> Perhaps some way to swap those two bytes?
>
> I know that there is no problem converting a hexadecimal number to a
> decimal string - I tested this by defining an oVar16 as equal
> to "0x02EE" and then using LCD.string=str$(var_name) and it
> successfully displayed 00750 on the LCD. However, I'm assuming there
> is going to have to be some magic in order for the text "EE02m"
> received by the serial port to be interpretted as the hex
> number "0x02EE" prior to such a conversion.
>
> Likewise, if I'm going to be sending values via SCP as well as
> reading them, I could use some pointers coding the OOPIC to
> convert numbers such as "750" to the appropriate two-hex number
> sequence required when sending data via SCP for storing to RAM.
>
> Thanks for any assistance,
>
> Mike
>
>
>
>
> Yahoo! Groups Links
>
>
>

--
------------------------------------------------------
Dennis Clark ooPIC Tech Support
www.oopic.com
------------------------------------------------------

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