Trigger field support

Trigger fields are a special hardware feature of certain types of terminal, such as the 8775. A field defined as a trigger field causes the terminal to transmit its contents if the operator moves the cursor out of the field when it is primed.

The field gets primed when the operator moves the cursor into it and enters data or uses either the DELETE or ERASE EOF keys. It becomes unprimed after it causes transmission, or if the operator uses the ERASE INPUT key, or after a send to the terminal (if you are using partitions, the send must be to the partition that contains the trigger field to have this effect).

You define a field as a trigger field by setting the VALIDN extended attribute to a value of TRIGGER, either in the map or by program override.

Only the field itself is sent when a trigger field causes transmission; other fields are not sent, even if they have been modified. You can detect a transmission caused by a trigger field by checking the attention identifier, which has a value of X'7F'.

Terminals that support the validation feature buffer the keyboard, so that the operator can continue to enter data while the host is processing an earlier transmission. The program processing such inputs needs to respond quickly, so that the operator does not exceed the buffer capacity or enter a lot of data before an earlier error is diagnosed.