Getting Started
I/O ADDRESSING
Figure 2-5 on page 2-23 shows the I/O addresses occupied by the
ZT 8809A, for both STD DOS and STD ROM systems.
I/O accesses are made via the full 16-bit I/O address, allowing for
64 Kbytes of I/O addresses. Eight-bit I/O boards are also compatible
with the ZT 8809A, provided the equivalent 8-bit addresses occupied
by the on-board devices are avoided. For example, the interrupt
controller at 0020 - 0027h prevents an off-board device from occupy-
ing any XX20 - XX27h I/O address, where X is a don’t care. Refer to
the timing diagrams in Appendix B for off-board I/O access times.
2-22
