This will depend on the CAMAC driver of course but the usual mechanism, when using CSL, is to return error codes from the Kmax device driver in the %_STATUS variable.  You can test, display or print the value of %_STATUS after each WRDIO command to determine whether an error code was returned. The information that can be returned depends on the type of CAMAC controller you are using. The usual meaning of the bits in the STATUS variable for most controllers is shown below. If a bit is set it indicates the following condition:
1–No Q
2–No X
3–Off Line
4–NoDriver
5–
6–Time Out
7–
8–Protocol Error