Asynchronous Serial Communications Programmer's Reference Manual (32022-90052)

Chapter 6 123

Typeahead Mode

Additional Typeahead Considerations

There are a number of actions that should be avoided when data is

being typed ahead, such as changing a terminal’s speed or parity

settings.

If you were to enter the speed command using typeahead, then change

the speed at the terminal and attempt to type ahead with the new

speed, the terminal would hang. Similarly, if you were to change the

parity setting before a typed ahead parity command could execute, data

would be lost. Either of these problems can be avoided by simply not

typing ahead when changing these settings. Wait for the commands to

execute before changing the terminal’s settings.

You will also encounter problems if you attempt to use typeahead with

VPLUS or user block mode. If your program allows block mode reads,

you should make sure that typeahead mode is disabled before the

terminal is placed in block mode. Because of the additional terminal

controls and status checks involved in processing a read in block mode,

it is not possible to use block mode and typeahead at the same time.

Finally, no attempt should be made to enable typeahead from a

terminal connected via PAD. Typeahead mode is not supported for this

conﬁguration.