VGA 20-column driver?

localroger · 2012-05-18 10:49

I find myself needing to replace a 4x20 VFD with an industrial LCD monitor driven by a Propeller. VGA.spin would be more than adequate but 32 characters wide is too dense and 15 isn't enough. Has anybody had luck adjusting the horizontal timing parameters for lower resolution? I've tried reducing vga_rate where it's set in vga_text.spin and scaling the horizontal dot counts appropriately, but I can't get the monitor to sync.

kuroneko · 2012-05-18 18:44

Try this (20x18, 800x600 timing):

vga_params              long    0               'status
                        long    1               'enable
                        long    0               'pins
                        long    %1000           'mode
                        long    0               'videobase
                        long    0               'colorbase
                        long    [COLOR="blue"]20[/COLOR]              'hc
                        long    [COLOR="blue"]18[/COLOR]              'vc
                        long    2               'hx
                        long    1               'vx
                        long    0               'ho
                        long    0               'vo
                        long    640             'hd
                        long    32              'hf
                        long    102{.4}         'hs
                        long    70{.4}          'hb
                        long    600    -24      'vd
                        long    1               'vf
                        long    4      +12      'vs
                        long    23     +12      'vb
                        long    32_000_000      'rate

Or alternatively (20x15, 640x480 timing):

vga_params              long    0               'status
                        long    1               'enable
                        long    0               'pins
                        long    %1000           'mode
                        long    0               'videobase
                        long    0               'colorbase
                        long    [COLOR="blue"]20[/COLOR]              'hc
                        long    [COLOR="blue"]15[/COLOR]              'vc
                        long    2               'hx
                        long    1               'vx
                        long    0               'ho
                        long    0               'vo
                        long    640             'hd
                        long    16              'hf
                        long    96              'hs
                        long    48              'hb
                        long    480             'vd
                        long    10              'vf
                        long    2               'vs
                        long    33              'vb
                        long    25_175_000      'rate

localroger · 2012-05-21 15:02

Thanks for the effort kuroneko. I got called out of town on another job and will probably get to try these Wednesday, will post when that happens.

localroger · 2012-05-23 10:17

Update: I finally got back to the office and tried these, both of them sync perfectly on all of my VGA monitors. I'll be using the 600x800 for this project since with vx=4 it uses a bit more of the screen real estate than the 640x480 with vx=3; both of these promise to be very useful. Much of what I do is low resolution but there is a big hole between 15 columns and 32 columns.

We really ought to have a library of known working alternate timings somwhere.

Dave Hein · 2012-05-23 11:00

I've used Kye's 640x480 VGA tile driver as the basis for other drivers, and it's worked OK with the monitors I've tried. His object generates 40 columns, but it's fairly easy to adapt to 20.

VGA 20-column driver?

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