Well, this is sort of embarrassing really.
Turns out it wasn`t the code or any mistake there (apart from that one line mentioned above), but rather a Hardware problem.
the New code you sent also did exactly the same thing too.
here`s my incarnation of the same circuit:

http://s1130.photobucket.com ...

Thanks!

I made that code change and indeed the Screen is now in 80 mode and looks Much better.
I did actually send you the wrong file(s) though, but it doesn`t make much difference as both have the "Memory Size" problem, it`s just that One is the RAM only mod.
Everything compiled just fine after ...

after making one of these basic units myself with just the board and few extra bit, I thought I`d try the Ram add on too.
It`s not going well for some Utterly Unknown reason (to me anyway).
I`m using the Same Ram chip (I bought 2 of them), the wiring has been checked 3 times by me on 2 different ...

if you send me the ROM Binary file, I`ll be happy to burn it onto a 27C256 for you, it won`t be a Fast ROM, but should do up to 4MHz without a problem, if that`s any help to you send me a DM

as I`m also searching for 5V tolerant CPLDs bigger than 128 cells, I came across these; http://uk.farnell.com/altera/epf8282alc84-4n/fpga-flex-8000a-2-5k-gates-plcc84/dp/1549403

this one having 208 LEs in the PLCC package, but they go up to 504 LE`s in PLCC too.
here`s the data sheet for them: http ...

just had this in my twitter feed: http://hackaday.com/2012/12/11/breadboard-friendly-fpgas/
the comments and mentions of other boards later on may be as interesting as the article itself eventually too.
I`m also chatting/hinting/urging/arm twitsing a designer friend of mine to develop a small FPGA ...

I`m unfamilliar with EhBasic, but yes, it`s the Break code for many versions of basic, and I can`t use it because I forgot to add the CRTL keys code in library, I`ll get around to though.
in fact I`m pretty sure someone did write a better Keyboard library for GCBasic already, I`ll have to find it ...

neat, so in effect you could swap out the LCD library and replace it with a Serial library and then use that directly to your SBC serial port.
Like yourself I also haven`t added data for the CRTL key on mine, so CTRL-C (break) has to be done by hitting the reset switch :)
and although it`s a fairly ...

looks about right :)
in that case then, if you Really wanted to, you could swap out the PS2 connector on the board and put a USB Female one in its place if you needed a smaller form factor.
the neat thing with the clock/data lines is that even if you did get them the wrong way around first try, it ...

I use the Altera 7128ELC84 here, along with a PLCC to DIP adapter board, there is a larger version in the MAX7000 series with more LE`s but I`v yet to find one on ebay.
a word of caution though, if you`re going to use the 7000 series chips make sure it`s followed by an `S` like 7064S or 7032S etc ...

yeah, SBC to PC is pretty easy with the FTDI chips (about £2 on ebay), or even the PIC 18f22k50, 18f2550/4550.
the s/ware I did was the other way around, where it parses a USB Keyboards data into Parallel and Serial output for the SBC to use.

as for the green adapters I`v no idea if they`re ...

if you don`t mind me asking, I`m curious as to Why your using the PS2/USB adapter and not just plugging it in directly to a USB socket?
very few of these adpters are Active devices and are merely pass-through, with D+/D- going directly to Clk and Data, GND/+5V remain the same.
a simple beep test ...

for what it`s worth, if anyone needs one and can`t find any, I have 17x 63B09`s here all pulled from working machines.

I`m intrigued by the 68C50 idea, if the humble 1MHz 6850L will cope with a CPU running at 8+MHz, then it seems reasonable to assume that a faster UART could handle a higher CPU speed, maybe even 16.384MHz?
the problem Now of course is that everywhere I`v looked doesn`t have any.
So... any ideas ...

I started with the 65c02 P4 chips and never really considered overclocking them, then someone mentioned the WDC version at 10MHz (I didn`t even know such a beast existed) so I won 5 brand new ones on fleabay and never really looked back.
as with some of my other computer designs, I like the idea of ...