Micrologix 100 rs232 port

Hi all,

the ab family of plc's is not new, but the micrologix 1100 is new to me and my new task is definately a first.

our production line is now required to weigh part of the final product before placing it in a box. we have a weigh scale that uses rs232 and we are looking at the micrologix 1100 to interface to.

we have a package consisting of a 2 part glue. we need to confirm that part a and b are in the sealed package which weighs lets say 1000 grams.

if the package has (2) of part a, we would get 850 grams or if (2)of part (b) we would get 1200 grams.

if the package weight is outside our limits we set using a panelview terminal, we are to turn on a red light signaling a fault, and the plc is to do several other operations as well.

Does anyone have any experience with the rs232 port and how to interface with it?

thanks in advance,
james

This sounds like a straightforward ASCII function application. The MicroLogix 1100 has a combo RS232/RS485 port but the normal 1761-CBL-PM02 cable works fine for connection to DTE-type RS232 ports (like your laptop).

Does the scale automatically send out a string with the weight value, or does it require an ASCII trigger to reply with the weight ? I've seen some scales with digital input triggers too.

When devices are sending "random" strings of ASCII input that can come at any time, I like to just periodically execute ACB instructions to return the number of characters in the buffer. When that value is equal to the number I expect, I execute an ARD ASCII Read instruction to get those characters into a String data type.

The use of the ASCII Clear Buffer, Check Buffer, Read Buffer and Read Line instructions will depend on whether your device sends the same number of characters every time, or uses a delimiter (usually Carriage Return, Line Feed, or both). Get the MicroLogix 1100 Instruction Set Reference and read up in the chapter on ASCII port and string instructions.