ComputerVoltageSources

It depends.  This is where I started.  I had a really nice serial 
VFD display.  I figured out how to use the S_OUT pin for an extra 
output and interfaced this to the display.  However, timing is the 
issue.  Since I used my hardware serial for MIDI, you have to use 
software serial for any other pins.  Software serial timing is 
incompatible with interrupts so you can't reliably talk to the 
display and use either the timer or MIDI interrupts.  I do use both 
MIDI and timer interrupts so this was an issue.  One way to solve it 
is to always disable interrupts prior to the display but since MIDI 
is at 31250 and the displays typically are at 9600 you will loose 
MIDI notes.  Also, your code gets littered with enable and disable 
statements.

A parallel interface is a waste of pins.  These LCDs take 11 bits.  
Plus the overhead is tremendous.  Each line is non-contiguous with 
the next.  There is a 64 byte offset between the first characters of 
each line and horizontally scrolling is a real pain if you want 
the lines contiguous (e.g. line 2 starts at the end of line 1).  As 
such, I used a $3 microcontroller to minimize the number of lines 
and manage the overhead of the display.  I believe all of these 
RS232 serial displays do the same.  However, you still have the 
timing issue with interrupts.

I ended up encoding my serial communications stream to the display 
as a MIDI sysex command.  Thus I could use the interrupt mechanism 
to communicate with the display and not have any MIDI or timer 
issues.  That was the benefit of the microcontroller.  And, once you 
have it, you can use any of the $10 LCDs with a parallel or non-
RS232 serial interfaces.  You could also use SPI but that requires 
more pins.  I'd rather save my pins for I/O and not the display.

Just what I found with my experimentation.

Dave


--- In ComputerVoltageSources@yahoogroups.com, Eric Brombaugh > None 
of these options would require anything more than
> a power/data header on the main board.