HP 3000 Manuals HP 3000 Manuals
VTURNOFF and VTURNON Intrinsics
The recommended practice for programming VPLUS applications is to use
only VPLUS intrinsics to perform terminal input/output operations.
Occasionally, however, a VPLUS application must interact with the
terminal without using a form. The following sections explain the
rationale for using these intrinsics and provide usage information and
examples.
Rationale for Usage
In order to use methods of terminal input/output other than VPLUS, the
application must switch out of VPLUS mode. This could be accomplished by
calling VCLOSETERM, then calling VOPENTERM to return to VPLUS mode.
These intrinsics, however, can have undesirable effects if the terminal
input/output mode switch is only temporary. For example, this intrinsic
pair can:
* Logically close the terminal.
* Clear the screen image.
* Clear and reset the terminal cache if the terminal local forms
storage is being used.
VTURNOFF and VTURNON provide a more satisfactory solution, because they
support temporary application switches from VPLUS block mode to character
mode and back again. Consider using VTURNOFF and VTURNON when the
application must:
* Switch to a command-level interaction.
* Send data to a slave printer.
* Display bulk data from a file retrieval.
* Write an addendum below the existing form.
Using VTURNOFF and VTURNON in Applications
The normal terminal input/output loop in VPLUS is a call to VSHOWFORM
followed by a call to VREADFIELDS. Besides presenting data, VSHOWFORM
also prepares the terminal for the companion VREADFIELDS. The recommended
placement of the VTURNOFF/VTURNON pair is prior to calling VSHOWFORM.
If your terminal input/output inside the VTURNOFF/VTURNON pair clears the
screen, you must always follow VTURNON with VSHOWFORM to restore the
previous form or present the next form. (For the previous form, you need
to set SHOWCONTROL bits (13:3) because VPLUS does not know that you are
clearing the screen.) If you are not clearing the screen, a reshow is
still appropriate (without the SHOWCONTROL bits). VPLUS optimizes
VSHOWFORM and only does what is needed.
It is not recommended to restore the screen using VGETNEXTFORM with
nfname in the VPLUS COMAREA set to $REFRESH. This feature is intended to
physically recover a terminal and synchronize the terminal and the
terminal driver. You would use $REFRESH if the terminal experiences a
power failure or hard reset. The $REFRESH process is much longer than
simply using VSHOWFORM to restore the previous display. Additionally,
$REFRESH invokes many of the VOPENTERM functions that VTURNON avoids,
such as the clearing of the local forms storage cache area.
Figures 2-1 through 2-4 show various usages of VTURNOFF and VTURNON.
___________________________________________________________________________
| |
| ... |
| VSHOWFORM |
| | |
| VREADFIELDS |
| | |
| The user selects the command mode function key. |
| | |
| VTURNOFF |
| | |
| This is your own terminal I/O, including clearing the screen. |
| | |
| VTURNON |
| | |
| VSHOWFORM This is the same form with SHOWCONTROL bits (13:3) set.|
| ... |
| |
___________________________________________________________________________
Figure 2-1. Switching to a Command-Level Interaction
_________________________________________________________________________
| |
| ... |
| VSHOWFORM |
| | |
| VREADFIELDS |
| | |
| The user selects the print function key for the slave printer.|
| | |
| VTURNOFF |
| | |
| This is your own terminal I/O through to the printer. |
| | |
| VTURNON |
| | |
| VSHOWFORM This is the same form without SHOWCONTROL bits. |
| ... |
| |
_________________________________________________________________________
Figure 2-2. Sending Data to a Slave Printer
__________________________________________________________________________________
| |
| ... |
| VSHOWFORM |
| | |
| VREADFIELDS |
| | |
| The user selects a key value for retrieving a bulk file. |
| | |
| VTURNOFF |
| | |
| This is your own terminal I/O, writing below the existing form, |
| reading 'continue' responses until done. |
| | |
| VTURNON |
| | |
| VSHOWFORM This is the same form, with or without SHOWCONTROL bits, |
| depending on whether the original form was maintained by|
| a memory lock. |
| ... |
| |
__________________________________________________________________________________
Figure 2-3. Displaying Bulk Data from a File Retrieval
__________________________________________________________________________
| |
| ... |
| VSHOWFORM Set SHOWCONTROL bit 10 to keep the keyboard locked. |
| | |
| VTURNOFF |
| | |
| This is your own terminal I/O, writing an addendum below the |
| existing form. |
| | |
| VTURNON |
| | |
| VSHOWFORM This is the same form without SHOWCONTROL bits 10, 13,|
| 14, and 15. |
| | |
| VREADFIELDS |
| ... |
__________________________________________________________________________
Figure 2-4. Writing an Addendum Below the Existing Form