Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!cs.utexas.edu!rutgers!dptg!att!chinet!edlee
From: edlee@chinet.chi.il.us (Edward Lee)
Newsgroups: comp.sys.ti
Subject: Re: Addressable memory
Message-ID: <8998@chinet.chi.il.us>
Date: 19 Jul 89 00:02:27 GMT
References: <4752@psuvax1.cs.psu.edu> <1643@csm9a.UUCP> <176@zip.eecs.umich.edu> <8958@chinet.chi.il.us> <1664@csm9a.UUCP>
Reply-To: edlee@chinet.chi.il.us (Edward Lee)
Organization: Chinet - Public Access Unix
Lines: 38

In article <1664@csm9a.UUCP> kamann@csm9a.UUCP (kamann) writes:
[....]
> would it not also be safe to say that the TI "generally" has more than
>32k of addressable memory?

It would be safe to say that the TMS9900 in the TI-99/4A can always
address more than 32KB of addressable memory.  The memory can be
addressed, but it might not be there.  The TI-99/4A computer has a
16-bit CPU and an 8 bit data bus.  The 16 bit word length of the TMS9900
allows it to linearly address 64KB of memory.

Incidentally, I programmed in TMS9900 assembly language when I was
fifteen or sixteen years old and believe that the TMS9900 in the
TI-99/4A operates at a clock frequency of 10Mhz instead of 12Mhz,
as has been previously claimed by someone else in this newsgroup.

>  Although the architecture is not there, something
>along these lines [of addressing more than 64KB of memory]
>could be developed from a software standpoint.  [Agreed.]  In addition,
>the TI has 64k on it once the memory expansion is hooked up, and it is all
>addressable, although not LINEAR.  [Agreed, but it should be mentioned
>that there is non-CPU RAM in the form of GROM/GRAM (TI's own proprietary
>memories).]  I guess it comes down to a definition of terms.

Well, I think we have agreed on using the term LINEAR to describe
memory that is accessed by a CPU without memory bank-switching (or
swapping, or paging, if you prefer).  The TI Extended BASIC cartridge
version 1.10 has around 38KB of firmware in it, but 38KB is an
unusual size for computer memories.  So, I suspect that the 
TI Extended BASIC cartridge bank-switches firmware to the
8KB (? It's been a while) area of CPU RAM reserved for cartridge
memory as it is needed.  I believe the same for the Tunnels of Doom
cartridge.  Someone please correct me if I am wrong about these
particulars.  Paul Charlton?


-Ed L
edlee@chinet.chi.il.us