NASCOM Microsoft Basic 4.7 conversion

Like to give a shout-out to Grant Searle and Phillip Stevens for having this code up on their sites and for the work they have done.
That said I looked at their work for some reference, but took the original Code and edited it to compile on the z88DK compiler.
I also did not use their modified code or interrupt-based polling, but software polling of the serial device.

Current code compiles, and port addresses are for my Z80 SIO, and should be simple to modify for other port addresses and other serial interface chips.

Current compiles just under 8K, I hope maybe to modify the Cassette load function since it uses the serial port on the NASCOM to load and save files vis the serial port and be able to keep code in the 8K ROM size. I am sure there is a lot of cleanup and other things to do. Will update as I improve the code.

Code at the start of the program for serial I/O operations commented also left original code in place for reference of the function of the routines.

I have a Facebook group called Zilog Z80 DIY

Note: Control C breaks out of program

1/6/2023 updated serial port code.