Maybe this is related to the posts about modern video hardware, but I am not sure. I am currently using a C1084S with my C128DCR and in order to switch column mode I have to press the 40/80 key on the keyboard and a button in the back of the monitor.
Is there a monitor (modern or not) that will sense the input video switching from the C128 and change the column display automatically?
Don't know of any CBM monitor (or IBM monitor) that does this. Yeah reaching behind the monitor is annoying!
There are some TV's / (modern) Monitors that will do this. This means you would have to convert the RGBI of the C128 to something they accecpt like S-Video or VGA... assuming you don't want 80-column monochrome (yuck). Also if the monitor does not have either composite or S-Video input (only VGA inputs) then you would also need to convert the VIC output.
On related lines, there are multi-input "video switchers"; I've seen multiple-composite (not recommended), mixed composite plus S-Video (good choice, but rare), and multiple-VGA (easiest to find, but you need convert both VIC and VDC outputs).
So unless somebody knows of a CBM-compatible monitor that does auto-switch, it looks like you would need at least one converter for your C128. I have to use the remote of my TV to switch between 40 and 80 columns... not as nice as auto-switch, but better than walking behind the TV and flipping switches or swapping cables
That cares of the hardware.
For software, you want some program wedged into the IRQ (err, I guess you could hack your own ROM) that will disable one or the other of the video outputs when you press 40/80 key. I read about one somewhere... it would disable VIC output (via undocumented 'test bit') and set CPU to 2MHz when you pressed down 40/80 key, then enable VIC and set CPU to 1MHz when you released the key.
I don't think it disabled the 80-column output ever. Which means it relies on the TV/monitor/switcher to give priority to whichever input is the VIC. Might be able to change the software to disable 80 column somehow... like set VDC to 8x1 mode which normally doesn't work?
Or if you're really hard-core, you could hack the hardware in the C128 to alternatively "kill" one of the outputs of VIC and VDC sync based on the key press. I wouldn't try that, but thought I should mention it.
Or just have two monitors up and running, 1702 and 1084. For those times when you need to see both screens due to double output like you can do with the Hydrophile's BASiC 7.80 Conceivably you could have 5 display device running concurrently, composite, separated, RF, monochrome and RGBi. I've actually done it just to see the difference in picture quality. The composite monochrome out looks best going into the separated video luminance input.
Let us not talk falsely now The hour is getting late