Re: LZ: Re: RAM I/O Expander
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Re: LZ: Re: RAM I/O Expander
On Fri, 13 Sep 1996, greg wrote:
> Wait a sec.. Wait a sec... lets get the RAM I/O expander actually working
> and see how fast it goes and if it even works before we start questioning
> it. By looking at the schematics, it looks very feasible. I'm afraid that
> if we starting commenting about how slow it is and stuff, people will start
> to look down on it, people will start to doubt it, and basically, no one
> would really care about it anymore. It would be a MAJOR revolution in
> calculating if we could add 8 megs of memory and a modem. Even if it did go
> at 300 bytes per sec, why do you need all that speed?? If you keep all the
> needed progs in the TI memory, then it won't matter. I would just use the
> expansion for backup and stuff like that. Even at 300 bytes per sec, it
> would still be relatively quick considering that most of the programs are
> only about 3k any ways. So anyways, lets see if it works, then critique it,
> not critique it before we see it.
I have an old (circa 1983) Radio Shack Model 100, which is the
original laptop computer. They came with 24k and were upgradable
to 32k. It uses an 8085 cpu, which is almost the same as an 8080,
the predecessor of the Z80. The lower 32k, like in the 85, is rom.
I bought an upgrade for mine to 64k. Upgrades up to 184k are available.
No rom change was needed. The way they did this was to use a poke in
Basic, or a write to a memory mapped port, I suppose, to switch in a
new bank. The rom knows nothing about this. A program can't really
access the extra ram, but it can be used for storage to leave more
room in the 32k for the running program.
Actually I just remembered that the above is only the way it seems
to work. In fact there is only one bank but that poke somehow causes
the contents of the normal bank to be swapped with the contents of
the other bank. Ok Ok. I'm no engineer. It's something like that
anyway.
I have no idea if this concept is doable on the 85. But if it is,
it might be a way to overcome the memory limit, at least in part.
Barry
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