Re: AltairZ80 simulator updated

Udo Munk wrote:

.... snip ...

Example for real memory mapped I/O are the 8080 and Z80 systems
that switched their ROM off by a JMP instruction, usually to
address 0. The read access to memory address 0 would trigger I/O
that takes the ROM offline and places RAM into this address range,
re-programming some sort of MMU that way.

I built my 8080 systems with a dual flipflop that was reset by the
reset pulse, and then counted up to three (a shift register). It
counted memory accesses. Until it hit three the high byte of the
memory access was supplied by a dipswitch (or patch board plugging
into a socket). This let me start execution on any of 256 possible
pages. Never had any urge to change it. The basic reason for the
construct was that, at time of conception, I had no idea what my
eventual monitor was going to look like.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home.att.net>
Try the download section.


.

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