Checksum for Equipment Communication

[Lou Picciano]

Whoops! Of course, Phil is exactly right - the checksum bit of your problem is exactly 'ASCII add' 

(sorry, read too fast - a lot of other kinds of checksumming in my head.).. 

----- Original Message -----

From: "Phil Potter (ou)" <Phil at pgpotter.demon.co.uk> 
To: omnisdev-en at lists.omnis-dev.com 
Sent: Thursday, January 8, 2015 12:11:52 PM 
Subject: Re: Checksum for Equipment Communication 

Presume ASCII ? 

Seems you just add up the Ascii character code for each character in 
your data string and then mod 256 to get a number between 0 and 255 for 
the checksum. 

The function asc() in Omnis might help here... 
or you may need to use bytemid() if your in a later version of Omnis. 

regards 
Phil. 

On 08/01/2015 16:55, Michael Mantkowski wrote: 
> Does anyone here understand What I need to do to create the checksum for the 
> following line of text I want to send to a lab text machine? I have all of 
> the communications setup and working via TCP/IP. But I am not quite sure 
> how to calculate the checksum. 
> 
> Data: 
> 1H|\^&|||ClienTrax|||||DiasysTech1^R910^280001||D|E1394-97|20141219091727 
> 
> I believe I get a Checksum of the above then add a <STX> on the front and 
> <CR>Checksum<ETX><CR><LF> on the back. 
> 
> This is what the mfg says needs to be done... 
> 
> During the transfer phase, the sender transmits messages to the receiver. 
> Messages are sent in frames that contain a maximum of 247 characters (7 for 
> control and 240 for the message itself). Messages longer than 240 characters 
> are divided between two or more frame. So there are two type of frames, 
> Intermediate and End. 
> Each frame starts with the <STX> character and a frame number that is a 
> digit ranging from 0 to 7. The frame number begins with 1 with the first 
> frame and it is incremented by one for every new frame, rolling over to 0 
> after 7. This number permits the receiver to distinguish between new and 
> retransmitted frames. 
> The checksum permits the receiver to detect a defective frame, and is 
> encoded as two characters that are sent after the <ETB> or <ETX>. The 
> computation for the checksum does not include <STX>, the checksum 
> characters, or the trailing <CR> and <LF>. Each other characters are added 
> to the checksum modulo 256. The checksum is an integer represented by eight 
> bits that can be considered as two groups of four bits. Each group is 
> converted to the ASCII character of the hexadecimal representation. The two 
> characters are transmitted as the checksum. 
> 
> 
> ********************************************************************* 
> Michael Mantkowski 
> ClienTrax Software 
> 1-614-875-2245 
> ********************************************************************* 
> 
> 
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> 
> -- 
> Phil Potter 
> Based in Chester in the UK. 
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