Data keys are those keys that generate characters that are in the extended ASCII character set; that is, those with ASCII codes in the range 128 to 255. During an ACCEPT operation, pressing one of these keys simply places the character into the field. However, it is possible to disable a key completely or make it terminate the ACCEPT operation (similar to the action of a function key).
ASCII codes in the range 0 to 31 can be considered as either data keys or control keys. For most purposes, they are treated as control keys and are disabled as data keys.