Maple Systems MAP450D - Manual (Page 27)

In addition to the standard printable ASCII characters, the host controller can also display
characters from the OIT’s extended character set. Refer to Appendix C: Extended
Character Set for a list of the extended characters available on the MAP450D and the
ASCII codes the host controller should send to display them.
The host controller can control the location of data on the OIT’s display by sending
control commands and control codes. For example, to move the OIT’s cursor down to the
next line, the host controller sends the LF control code (hexadecimal 0A). To move the
OIT’s cursor to Line #2 Column #10, the host controller sends the Set Cursor Position
control command (
ESC
x 10 2 terminator). Refer to Appendix A: Control Commands and
Appendix B: Control Codes for a complete description of the available control commands
and control codes.
The OIT continuously monitors the host controller for data. Therefore, the host controller
can send data to the OIT at any time. The OIT uses a 200 byte internal storage buffer for
incoming data from the host controller. This buffer can fill up if the host controller sends
data faster that the OIT processes it. If this occurs, use software or hardware handshaking
to control the rate of data transfer. Refer to Chapter 1: OIT Configuration for information
on software and hardware handshaking.
Using a Display Variable
One display variable can be defined at any time on the OIT’s display using the Create
Display Variable control command. A display variable allows the host controller to set
aside a portion of the OIT’s display for specific data. When writing to the display
variable using the Write Display Variable control command, the host controller does not
have to worry about where the OIT’s cursor is positioned or whether the OIT operator is
in the middle of entering data. One typical use for display variables is to set aside a
location for displaying time-critical data such as error messages. Following is information
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.
Chapter 3: Using the OIT's Display 26
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