IBM 3164 ASCII Manual page 150

if it has not been modified yet. In this case, the must-fill validation test does
not take place.
The display station performs a must-fill validation test when the cursor is in a
must-fill field whose contents have been already modified and you perform
either of the following:
1. When you try to move the cursor out of the field.
2. When you try to initiate an inbound data transmission.
The must-fill validation test searches the must-fill field for null characters.
• If a null character is found, the keystroke that caused the validation test is
not processed, the cursor is not moved out of the field, and the Must Fill
condition is raised. You can fill the field with non-null characters, and
then move the cursor out of the field or repeat the enter action; the display
station then repeats the must-fill validation
te~t.
• If no null character is found, then the keystroke that caused the validation
test is processed normally.
Notes:
1. Right Justified, Must Fill, and Must Enter have no effect if specified
for a protected field.
2. If a field is classified as a must-fill/must-enter field and as an
auto-send field, the must-fill/must-enter validation test is performed
before the auto-send field action.
3. Use of the Page or Jump key is independent of the must-fill validation
test. If you switch to another page or partition while the cursor is in
an unmodified must-fill field, the screen cursor leaves the field, but the
CCA for the page is not changed and the must-fill validation test is
not performed. When you switch back to the original page or
partition, the original situation is recreated as if the screen cursor had
never left the page or partition.
4. The must-fill/must-enter validation test is applied to the field between
the send starting and ending addresses.
An auto send field is a field whose data are automatically sent to the host
program as soon as you have modified a field (if the field data transmission
mode is set to the modified field data transmission mode) and you move the
cursor out of that field; this allows the host program to receive and to validate
fields one by one.
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