Re: A85: Memory Mapped Devices
[Prev][Next][Index][Thread]
Re: A85: Memory Mapped Devices
On Tue, 28 Oct 1997, Keith Burzinski wrote:
> Does anyone know how Memory Mapping is done? Like, for example, the
> screen on the TI-85 or 92? I'm not looking for anything real specific,
> just a somewhat general explination as to how it is done/how it works.
> And actually, something more from a hardware standpoint. ;)
As I understand it, memory mapping (as in memory-mapped I/O) means that
the I/O and the physical RAM/ROM exist on the same port of the CPU. In the
Intel style, there are separate ports for the I/O and the memory, but on
other processors (like the 68k, Z80, etc) use the same address and data
buses for both memory and I/O.
All this is useful because it makes the address possibilities for I/O
immensely larger. It also makes certain data processing instructions run
more quickly on the CPU.
In your example, the LCD screen on the calc exists through the same port
of the processor as the RAM/ROM. That makes possible nearly all of the
functions that you might normally use on RAM..
Did anybody make sense out of what I just said..?
--
Greg Hill
greg-hill@bigfoot.com
www.comports.com/link
References: