AB PLC internal structure

C

Thread Starter

Cesar Garcia

Hi,

The A.B. DH+ communication protocol describes how to read or write an specific position in a PLC5 but it doesn't says how the program is structured, it means, how can I know what position I have to read in order to obtain a N7:0 data, or how many programs and data files exists in the PLC5 memory?

I would appreciate any information related or where to download it..
 
M

Mark Fairbaugh

The number of program and data files can be different for every PLC-5. That is all setup by the user, but limited by the Processor memory size.

I have several PLC-5/40 here and have from 10-100 program files and from 25-100 data files.


Mark Fairbaugh
PT Newmont Nusa Tenggara
Sr. Process Control Engineer
e-mail: [email protected]
Phone: (62)-370-636-318 Ext. 47948
Mobile: (62)-812-382-0235
 
Hey,

The "PCCCD" contains info similar to what is in this document:

http://www.ab.com/manuals/cn/17706516.pdf

The "Programmable Controller Communication Commands" for DH+ and DF1 are the same but the protocol (method) wrapper are different.

A read of "N7:0" would look something like this.

Example:0F00TTTTA102078900

0F = CMD or COMMAND.
00 = STS or STATUS.
TTTT= TNSW or TRANSACTION WORD lsb and msb.
A1 = FNC OR Function byte.
02 = I am going to read two bytes of data.
07 = File number as in 7.
89 = Integer file type. (N)
00 = File read offset or start of my read.

Simple huh.

Remember that "Communication Commands are usually in hexadecimal (base16) and at times byte swapped.

You will find that there are not simple ways of finding some info.

Play with it and have fun..

Joseph Doty
[email protected]
 
Hi!

I have made significant progress in reverse engineering the DH+ protocol used with AB PLC5's. The bulk of my work, though Linux based, is quite easily applied to any computer platform. My work is freely available in source-code only form. The library may be found and/or downloaded from http://freshmeat.net

Searching the phrase "allen bradley" will turn up the source code for my project.

Enjoy!

Ron Gage - Saginaw, MI
([email protected])
 
Mr.Joseph Doty, thanks for your infomation of 'read command' format. Now, can u tell me the write command format of the DF1 protocol? lee Ng.
 
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