Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!ucdavis!uop!mrapple
From: mrapple@uop.edu (Nick Sayer)
Newsgroups: comp.os.cpm
Subject: Intel hex (*.HEX) format questions
Message-ID: <1796@uop.edu>
Date: 24 Feb 89 04:23:57 GMT
Organization: Amateur Radio: N6QQQ
Lines: 51

Anyone have some cold, hard facts concerning the Intel .HEX format?
I've managed to figure out a little bit of it, and have come up with
this:

Each line looks like this

:10020000C30CDFC308DF7F00202020202020202007
^ ^   ^ ^^                              ^ ^
| |   | ||---8 * num bits - data bytes--| |
| |   | |                                 |
| |   | |    Checksum---------------------+
| |   | |
| |   | +----Always 0. Why?
| |   |
| |   +------16 bits - address to start
| |
| +----------8 bits - the number of bytes on this line
|
+------------always a :

Final line looks like this

:0000000000
^ ^   ^ ^ ^
| |   | | |
| |   | | +-------Checksum
| |   | +---------Always 0. Why?
| |   +-----------Address. Can be non-zero, but what does that mean?
| +---------------Zero bytes on this line
+-----------------Always a :

What I wonder is; What does the "always 0" byte do? Is it always 0?
What is the algorithm for computing the checksum? I believe it is
like this (in c, s is the line)

int i,csum=0;
for(i=1;i>length(s);i+=2)
  {
    csum^=((s[i]&15)<<4);
    csum^=(s[i+1]&15);
  }

What happens when the address in the last line (with 0 length)
is non-zero? Does that mean that the entry point is at the noted
address or something?

---------------------------------------------------------------------- 
Nick Sayer | mrapple@uop.edu | Packet Radio: N6QQQ @ WB6V-2
uucp: ...!ucbvax!ucdavis!uop!mrapple
Disclaimer: "The BBC would like to appologize for that last announcement."
cat flames > /dev/null