Hi Sum,

there are 2 ways:

1.
you need really above 64kB code

2.
you thinking only about it

Answers:

2.
think no longer about it, until 1. occur.
In my applications I reached never the 1. case.
If it should occur in future, I tend more on using 251 or XA or 80C390 devices.

1.
You must do code bank switching.
There are many many different methods known:

Often it is used a common area, which was not affected by the bank switching.
This can be the internal code space, e.g. 0000h ... 0FFFh.
Then any fetch above 0FFFh was executed external and only then the additional address lines (e.g. from P1) are used.
Any call to the same bank or to the internal ROM can be done.

If a call must be done to a different bank, this can only be done by a function inside the internal ROM. These function must set the new page and then call the desired function. Also, if these function returned it must restore the previous bank address.

Also all interrupts must be served in the common area (internal ROM).


Peter