Field wiring terminal strips and module housings are slotted on the left and right sides of the PCB card slot to accept keying pins (see I/O Module Figure).

To prevent plugging the terminal strip into the wrong module, once wiring connections have been made. Keying is implemented at the discretion of the user.

Primary keying is provided on the right side of the module, marked A through F (top and bottom positions are coded the same). Primary keying provides module class coding. Primary codes have been pre-defined, according to the following tables.

Secondary keying is provided on the left side of the module, marked 1 through 6. Secondary keying codes are user-definable and may be used to identify module personality within module classes, or other unique site requirements.

The user may also use personality keying to differentiate between like module types (i.e., 140 DAO 840 00 and 140 DAO 842 10 both have the same primary keying pin combinations), using the white keys for each code.