ASCII Modules and RS232 device

[Tomo453]

Hello,
I have a linear actuator set up (2 Ewellix linear actuators with hall effect sensor encoders) and an SCU control unit with RS232 communications. The SCU provides a nice command set, and data, such as actual position of actuator1, can be directly accessed. The network layer for this is a Point to point connection. The control unit functions as slave and replies to the requests of the master (e.g. PC program). The slave replies to each request from the master. The manual for the SCU shows example code in C++ to be coded on a connected PC. I want to, at the very least, get the encoder readings from the SCU to calculate the position of the roller attached to the actuators and display this value. My first thought was to use a flat panel PC to run this code with a simple GUI to display the positions and possibly buttons to extend, retract and send the roller to a commanded position. My question is though, could an Allen Bradley ASCII module namely a 1734-232ASC (point I/O very proximate to the SCU of actuators) or a 1769-ASCII be integrated to perform the same tasks? I am new to these modules and possible configurations. Are there instructions to access specific data locations using RSLogix 5000 via the modules listed? Or is the entire data set polled and subsequently parsed in RSLogix.

 

[Mispeld]

I've had good, though limited, experience with the 1734-232ASC. My application was a simple command-response protocol, where both command and response were delimited by the carriage return character.

There are no special instructions for this I/O module. Outgoing and incoming messages are byte arrays in the module-defined data structure. Sending is triggered by incrementing a transmit message counter, and incoming messages are detected by a change of the received message counter. There is some flexibility with the module's data format. I only used the "short string" configuration, which allows for up to 127 in/out characters.

Once the receive buffer is copied into a string tag, the Logix ASCII instructions are available for parsing and data conversion.

 

[Tomo453]

I've had good, though limited, experience with the 1734-232ASC. My application was a simple command-response protocol, where both command and response were delimited by the carriage return character.

There are no special instructions for this I/O module. Outgoing and incoming messages are byte arrays in the module-defined data structure. Sending is triggered by incrementing a transmit message counter, and incoming messages are detected by a change of the received message counter. There is some flexibility with the module's data format. I only used the "short string" configuration, which allows for up to 127 in/out characters.

Once the receive buffer is copied into a string tag, the Logix ASCII instructions are available for parsing and data conversion.

Thank you Mispeld, this clarifies things considerably.

 

[Ken Roach]

The 1734-232AC and the 1769-ASCII module trade off some simplicity for some flexibility. They are very good for simple short ASCII serial transactions with terminating characters (like CR and LF) or fixed data sizes.

My quick review of the Ewellix SCU serial interface user manual shows that it's a binary protocol with variable length and a CRC16 checksum.

I've implemented protocols like that with the 1734-232ASC, and would not try to do it again. My most likely interface choice would be a Red Lion DataStation, or an HMS Communicator.

 

[Tomo453]

The 1734-232AC and the 1769-ASCII module trade off some simplicity for some flexibility. They are very good for simple short ASCII serial transactions with terminating characters (like CR and LF) or fixed data sizes.

My quick review of the Ewellix SCU serial interface user manual shows that it's a binary protocol with variable length and a CRC16 checksum.

I've implemented protocols like that with the 1734-232ASC, and would not try to do it again. My most likely interface choice would be a Red Lion DataStation, or an HMS Communicator.

Thanks Ken,
I read the user manuals for the ASCII modules and the literature on ASCII instructions. The Red Lion Data Station seems a better fit for me. I like the embedded OPC/UA feature. It is a powerful little tool. It will allow me to integrate some other components of the line as well.