Based on what I am reading from the EDS file:
Input Assembly:
Class 4, Instance 100, Attribute 3.
Output Assembly:
Class 4, Instance 101, Attribute 3.
When reading the data from an Assembly object, use the Get_Attribute_Single service code 0x0E (14). When writing data to an Assembly object, use the Set_Attribute_Single service 0x10 (16).
According to the EDS file...
The Output Data size can vary from 2 bytes to 104 bytes, with a default size of 12 bytes.
The Input Data size can vary from 2 bytes to 1400 bytes, with a default size of 394 bytes.
Things to keep in mind:
The maximum block size for a single EIPMSG request is 500 bytes.
The EDS file is used for configuring Class 1 Implicit Messaging connections. The BRX currently only supports Unconnected Explicit Messaging. Therefore, you may run into a few restrictions when attempting these Gets and Sets (e.g., you may be able to read input data, but not be able to write output data).
Give it a shot and see what happens.