Well both of these chips can probably be replaced with a simple micro-controller.Figured out another bit of the overall design... and jimblumberg, you may be correct on my need to find updated ICs after all - the MC6821 is no problem (W65C21), but I find the MC6840 generates both the output carrier timing AND the ~NMI signal for the CPU.
Decoding a 4x4 matrix keyboard is also fairly easy to decode with a simple micro-controller. IMO, it's trickier to properly wire the matrix than decode it.As far as a fresh rewrite goes, my plan of attack is to get code for a 4x4 matrix keyboard written
Again there are many many simple micro-controllers that have an I2C interface capable of driving a simple LCD. What kind of LCD will you be trying to use? Does it use any kind of graphics or is it a simple single/multiple line display, like a 1 x 16, 2 x 20, etc.followed by code to drive an I2C LCD,
Again there are simple micro-controllers that have built in timing, interrupt modes, and timer subsystems that make delay routines quite simple.then a proper delay routine
You also need to realize that the hardware you have is all geared to that outdated micro-controller. The 6800 series of controllers were fairly primitive without much of anything available internally. Almost all the functionality is contained in separate chips.
If you go for a complete redesign of the hardware you may be able to reduce the chip count significantly with the side benefit of added simplicity in both chip count and software.