Maybe the problem is that the Optrex display is built in a strange manner. These Hitach controllers allow for displays up to 40 characters wide. And the initialization process permits you to select one line or two line mode. The Optrex display you have may have implemented the display in the opposite mode as the other smaller test displays you were working with.

When an LCD manufacturer makes the glass for their module they may have elected to use one line mode and then make the traces on the glass operate as "one line" from the perspective of the controller but have the physical placement of the character locations on the glass appear as two lines.

Alternatively they may have elected to support the two line mode as one normally expects.

You may want to try changing the initialization you gave the Optrex module to see if that will make a difference in the operation of the BUSY flag.

Michael Karas