Uhhh... in the View Studio Tag Browser, although you can just type it in manually.
There is no indication of read or write direction when defining a tag. It is just a connection to a location in the target device (or memory).
The format for View Studio requires "::" to precede any connection that contains a colon
) character in it, as do all data table accesses to a Micrologix, SLC, or PLC (Purist's may note that you don't need a colon if you use bit access as in "B3/121").
The proper format for any reference to a physical device, either when defining tags in the HMI Tag Database or using Direct References is:
{::[TOPIC_NAME_DEFINED_IN_LINX_ENTERPRISE]LOCATION_IN_DEVICE}
The opening and closing braces {} are sometimes absolutely required, and sometimes optional. Save the hassle, and always use them.
The "::" was discussed above, your data files are organized as FILE_TYPE FILE_NUMBER : WORD/BIT (as in, N7:3/0) so they have a colon, and need this token.
The square brackets must enclose the topic name of defined in your OPC server (RSLinx Enterprise usually for ME) []
The topic name inside the brackets should be exactly the topic name you used to set up a communications link in RSLinx Enterprise.
Then, the "LOCATION_IN_DEVICE" is wherever the actual data is in the target device. B3:0/1, N28:151, T4:3.ACC, etc.