Maple Systems STEPware-100 - Manual (Page 47)

on creating, writing to, and deleting display variables. Refer to Appendix A: Control
Commands and Appendix B: Control Codes for more information.
To create a display variable:
1. Have the host controller position the OIT’s cursor in the location where you want to
start the display variable.
2. Have the host controller send the Create Display Variable control command (
ESC
w
length terminator). The area allocated for the display variable is cleared, starting at
the OIT cursor’s current location, and the OIT’s cursor is placed to the right of the
display variable.
To write to a display variable:
1. Have the host controller send the Write Display Variable control command (
ESC
v text
terminator). The new text overwrites the existing contents of the display variable. If
the text sent is longer than the display variable, the excess characters are ignored.
NOTE:If the new text is shorter than the existing text, the part of the existing text that is longer
than the new text will still be visible in the OIT’s display.
To delete a display variable:
1. Have the host controller send the FF control code.
NOTE:The FF control code clears the entire display not just the display variable.
Displaying Text from Predefined Messages
In some applications, the OIT may be required to display many messages to the OIT
operator concerning the state of the control system. If these messages are always the
same, they can be stored in the OIT and displayed whenever the host controller requests
them. The OIT has the ability to store up to 500 predefined messages. Each predefined
message can be as long as the number of characters per line on the OIT and can contain
printable ASCII characters and characters from the extended character set.
To display a predefined message, the host controller sends the Display Message control
command (
ESC
m message# terminator). When the OIT receives the Display Message
control command, the requested message displays at the OIT cursor’s current location. If
the message is longer than the number of character spaces remaining on the current
display line, the message is truncated, unless word wrap is enabled.
For example, the OIT programmer configured Message #25 to read “This is a message
text string!”. The following message is displayed on the OIT (notice the location of the
cursor in Line #2):
This is the first line of the display
Cursor is here:_
When the host controller requests Message #25 by sending the Display Message control
command (
ESC
m 25 terminator), Message #25 is displayed starting at the OIT cursor’s
current position in Line #2:
This is the first line of the display
Cursor is here:This is a message text s!
44 STEP1 Protocol Operation Manual
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