Reference to a VT220 terminal is intended to indicate a VT220 terminal equipped with a Selanar SG220 graphics upgrade board. The SG220 board operates through the VT220's printer port. In addition, it uses some of the keys on the VT220 keyboard. It is possible to enable the graphics board when the printer port is disabled. This causes some of the keys (notably the keypad and cursor keys) to not work for editing, etc. To correct this, deselect the graphics board using CNTRL-SELECT.
In order for the graphics board to plot graphics commands from the library routines, the printer port must be in the controller mode and the board enabled. All this is automatically handled by the LONGLIB graphics library routines. Note, however, that you will need to use the CTERM commands correctly to obtain proper operation.
The DCL command file VCLEAR.com will reset printer port, reset the graphics card to terminal mode, and clear the screen under most situations.
When using GETCURSOR, a large cross-hair will appear on the screen. Use the cursor keys and the shift key to move the intersection point to the desired location and press a key. This ends the graphics input. The cross-hair will disappear, there will be a pause, and the program will continue. NOTE: DON'T USE THE RETURN KEY TO END GRAPHICS INPUT AS THIS WILL CAUSE THE PROGRAM TO NOT READ THE LOCATION AND MESS UP YOUR TYPE-AHEAD BUFFER.
The SG220 board stores the starting and ending points of each vector in memory then dynamically redraws the screen for each refresh (this is how it can do zooming and windowing). However, this also limits the number of vectors that can be drawn on the screen at once. If a very large number of vectors are plotted, a zoom in/out may cause a portion of them to not reappear.
Note: Since the actual SG220 screen resolution is only 832x350 and the board is emulating a Tektronix 4014 (4096x3200) there is some quantization error associated with the cross-hair operation.
Note: When the manual zoom in/out feature is used the cross-hair cursor does not work properly. The cross-hair is initially plotted then erased. When you move the cross-hair, it is replotted. A copy of the cross-hair stays at the start location. Otherwise, it is useable.