There are special considerations when buffering input in POS-application OSDIs: to be meaningful, the input buffer should be able to contain at least 3 EANs (European Article Numbers). 5 EANs may be safer. In any case, the buffer must not contain part fields. Thus, if the buffer fills:
The user is warned, on completion of the last acceptable field, that further immediate input will be thrown away. This means that the warning needs to come up (maximum field length - 1) characters before the buffer is full. This may present problems if the user considers that an article has already been accepted (because, for example, a bar reader has beeped following a scan)
No input is accepted until there is room for a complete field. It may, in practice, be best to wait until the buffer is empty again and then prompt the user
There is an option in DFSETUP to modify type-ahead behaviour (choose Colours and Miscellaneous Cosmetics then Type-ahead). Type-ahead is managed in the DP4 Terminal Manager. If type-ahead is turned on in DFSETUP the DP4 Terminal Manager may continue to gather input while the application is processing previous data. This allows the DP4 Terminal Manager to scan for certain control sequences.
Note that the type-ahead buffer has a limited size - if input to your OSDI is likely to be rapid there is a possibility of exhausting the type-ahead buffer. Subsequent input will be lost.
If you are in doubt about type-ahead, use Operating System Type Ahead in DFSETUP. It is recommended that you do this if you are using multiple input sources.