Creating Checksum in PBP

[Bruce]

Just look at any ASCII chart to understand what's happening.

With PBP most people assume sending serial data goes something like this;

X VAR BYTE
X = 123

Main
    SEROUT2 0,16468,[DEC X]
    PAUSEUS 200
    GOTO Main

You would assume you're sending a single byte, but PBP is first converting your three decimal digits in X into three separate ASCII characters, and sending a total of three bytes. "1" then "2" then "3". That's what the DEC modifier does.

So your PC isn't receiving a single byte value of 123. It's receiving three separate bytes. ASCII characters 1 then 2 then 3. This is what it's using to calculate the checksum.

Since your PC checksum program runs a cumulative checksum calculated from each separate ASCII digit, you just need to do the same with your PIC-based cheksum program before sending the final checksum result to the PC.

Try running this with a PIC connected to your PC serial port, and see what displays in a terminal window.

X = 123

Main
    HSEROUT [DEC X,13,10]
    HSEROUT [X,13,10]    
    PAUSEUS 2000
    GOTO Main

[picnaut]

Hi,

The attached file may be of some help.

Cheers.