After this method is called the display will enter a diagnostics mode and stay in that mode until endDiagnosticSequence() is called. The diagnostic sequence starts by setting all pixels, then displaying the part number and firmware version, followed by stepping through every character in every character set. One character is shown at a time, filling all positions of the display for approximately 1 second per character.
vfd: a variable of the type Ncr4X20Vfd.
See UnitTests example.