Asynchronous Terminals and Printer Processes Programming Manual

TERMINAL PROGRAMMING CONSIDERATIONS
Page Mode
block immediately. The transfer terminates on detection of the
current page termination character. For ATP6100 subdevices,
you can redefine the configured page termination character by
including the PAGECHAR attribute in a CMI ALTER SU command.
Pseudopolled Page Mode
In pseudopolled page mode, the operator initiates the transfer by
pressing a function key. However, the terminal does not send the
data block until it receives a trigger character.
You have the option of choosing whether the I/O process or
your application issues the trigger character. The PPOLL SYSGEN
modifier specifies the trigger character. If the configured
PPOLL character is zero, the application issues the trigger
character; if the configured PPOLL character is other than zero,
the I/O process issues the trigger character. For ATP6100
subdevices, you can redefine the trigger character by including
the POLLCHAR attribute in a CMI ALTER SU command.
When the application issues the trigger character, the terminal
operator initiates the transfer by pressing a function key. The
application program obtains the function key identifier with
a READ call. It then interprets the identifier, sends the
appropriate trigger character to the terminal with WRITEREAD, and
reads the data block into the application buffer.
The advantage of having the file system handle the triggering,
of course, is that the operation is invisible to the application
program. Automatic triggering can be used, however, only when
issuing a READ (not a WRITEREAD) to the terminal. WRITEREAD can
still be used for such things as cursor sensing.
The advantage of having the application program handle the
triggering is that only one word of buffer space is used while
the terminal operator is typing. The buffer space is allocated
after the operator presses the function key. Terminals operating
in normal page mode require that the entire buffer space be
allocated while waiting for a transfer to take place.
Example
Here's how pseudopolling works: Your application program issues
a READ of one character to the pseudopolled terminal. This READ
waits for the ready character. For example:
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