Henk Tobbe wrote:

> M rescued a 1x8 LCD from an old printer and hooked it up.

  Context:  You mean 16 char x 1 line.

> Although one line, to get it working I had to treat it as a 2 line
> device.

  This is universal unless you have a display that uses the full 11-row
font (the "VGA" version of the LCD "CGA" world if you follow...).

  The driver chip has outputs for two rows of 8 characters.  If you
think about it, this means 16 rows and 40 columns, total 56 pins.  It is
most efficient to have similar numbers of rows and columns though 16
rows is close to the practical limit for multiplexing (which is a limit
of passive LCD displays which are all broken up into sets of 16 rows -
this may show in operation one way and another).

  Expander chips each provide the same number of columns using the row
multiplex from the first driver, so each adds 8 characters in each of
two rows.

  Along the principles known to most of this list, manufacturers are
*not* going to use an expander chip if there is another way to do it, so
single-line displays of 16, 32, 48 64 etc. characters use the first 8
multiplex rows for the first half of the display (the first display
"line" and the next 8 rows for the second half.  You may consider the
layout considerations...

  Does that make sense?

--
  Cheers,
        Paul B.