Support of Rack-optimized and Direct Connections
The 1734-AENT adapter supports both direct and rack-optimized connections. A direct connection is a real-time data transfer link between the controller and whatever module occupies the slot that the configuration data references. Direct connection messaging occurs at a cyclic rate specified by the RPI during configuration. A rack-optimized connection is a grouping of data from more than one I/O module into a single block of data sent over a single connection at the same data rate.
Rack-optimized connections reduce the total number of connections needed to transfer data when using many I/O modules in a system. The following example illustrates the benefit of rack-optimized connections.
Assume you set up a system that contains 8 digital I/O modules interfaced to a 1734-AENT adapter. If you use direct connections to transfer data to each of the these I/O modules, you need 8 connections to transfer all of the data, one to each of the 8 I/O modules. If you use a rack-optimized connection to transfer the data, you only need a single connection – the connection to the 1734-AENT adapter.
Although rack-optimized connections offer an efficient way to use resources, there are a few limitations on their use:
•You can use only rack-optimized connections to send data to and from digital I/O modules. Analog or speciality I/O requires direct connections.
•All data is sent at the same time as the RPI rate of the 1734-AENT adapter.
See the EtherNet/IP Performance and Application Guide, publication number ENET-AP001, for more information on connections.
Mix Rack-optimized and Direct Connections
You can mix communication formats for different I/O modules communicating through the same adapter. I/O modules set up to use rack optimization communicate at the rate of the RPI configured for the 1734-AENT adapter. I/O modules configured for direct communication communicate at their own set RPIs and ignore the 1734-AENT adapter’s RPI.
Publication 1734-UM011C-EN-P - January 2006
