Rockwell Protocol Documents

A friend just pointed out this public web page to me: How to Communicate with Rockwell Automation Products. While have seen many of this documents before, a few of them were new for me. It includes information on:

• How to talk to ControlLogix tag data via Ethernet/IP
• How to understand ControlLogix data structure packing when read raw
• The DF1 serial protocol specification
• How to encapsulate CIP over DF1 (ie: talk to serial port of Compact/ControlLogix)
• How to use Ethernet/IP explicit messaging to ControlLogix
• How to use Ethernet/IP I/O messaging with ControlLogix

In addition, I see www.ab.com has added a new DF1 supplement to its Knowledge Base. Since you have to login giving you a direct link is pointless, but it is called "DF1 Protocol supplement 17706516". It compares PLC5 and SLC5 communications, covers some useful commands such as 0x0AB "Protected Typed Logical Write with Mask" to write individual bits, and new data file types not covered in the latest 1996 version of the DF1 specification.

While we are discussing new Rockwell protocol information, you should also review and be aware of the new "DF1 Radio Modem" protocol. I don't think there is a form specification, but you can find a file in the http://www.ab.com/ Knowledge Base that describes the simple differences between it and DF1 Full-Duplex. In summary, DF1 Radio Modem *IS* DF1 Full-Duplex without the protocol ACK/NAK. It is designed for use in radio systems where the powering up of slave modems just to ACK something they will respond to anyway just slows down overall polling. I'm also finding it ideal for cellular IP networks since it literally cuts your data usage by 50 to 60% to NOT be moving 2-byte DF1 ACKs within TCP/IP which also includes a TCP acknowledgements. SInce DF1 includes a TNS or transaction number, there is no problem with mishandling lost or delayed messages.

The main catch today is that I think neither RSLinx nor ControlLogix support DF1 Radio Modem - it is mainly a MicroLogix and SLC5 family resource. However the next release of the Digi One IAP will include the ability to bridge to DF1 Radio Modem from Ethernet/IP, CSPv4 (AB/Ethernet) and DF1 Full-Duplex.