Jay Mielke wrote:

> I am trying to get an Optrex 4X16 LCD to work (HD44780) using the code
> from Peter Ouwehand's home page.

  Ah yes.  I didn't have that filed under his name, but it is one of my
*major* references!

>  The catch is I am using a 16C74A as opposed to the 16C84.  Has anyone
> else tried this?

  Should work fine.  Minimal differences.

>  I turn the circuit on and the first and third lines of the LCD are
> filled in with block characters, the second and fourth lines are
> blank.  I am using the full 8-bit interfacing.

  The display uses "two-line" mode.  The "second" line is as you have
found, actually the second and fourth lines.  Looking for "Function Set"
in http://www.iaehv.nl/users/pouweha/lcd0.htm#instruction_set you will
note that you have to set up bit 3 ("N") as a "1".  For you, the command
value will be $38 or $3B.

  He appears to have fixed the typo I reported.  Good ;-)

  Note the display addresses of the four lines.  They are tabulated in
http://www.iaehv.nl/users/pouweha/lcd.htm which *also* reminds you of
the correct value for "N".  The first line scrolls automatically to the
third, and the second to the fourth.
--
  Cheers,
        Paul B.