Re: TI-H: Parallel Memory expansion

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Re: TI-H: Parallel Memory expansion

>> The Expander II and III are both in development right now, and should
>> be available within a few months.
>> 
>Cool; I hope whatever I build will have it's own niche though. :)

I'm not saying that you won't do it, but *guess* how many people have
emailed me describing their own expander project that will use
parallel flash chips or some other form of mem?  You're #6!  Many of
them are already far on their way.  But frankly I don't see one coming
out, at least not anytime soon.

>> Yes, there are two new places that are selling high capacity serial
>> flash EEPROMs but neither are easy to interface to and neither are
>> compatible with the current schematic.  There is a two-wire 8Mbit
>> flash chip coming out in like 5 months from this place, but I probably
>> won't use it if it's expensive.  The others are all SPI bus which
>> means a minimum of 4 wires are needed (5 or 6 are preferred), whereas
>> the TI only has 2.  That is why a microcontroller is the easiest way
>> to go, and it also allows you to do a lot of cool stuff :).
>
>The schmatics I've seen need 3 wires, a Clock, data, and the ground,
>which the TI-85 can do just fine.

Are you talking about I2C parallel/serial I/O converters or actual
serial flash EEPROMS?  There is no 2 wire interface high capacity
serial EERPOM on the market today, that's a fact.  One *is* coming out
though but I probably won't be using it unless it's very cheap (I
haven't see pricing specs for it yet).

>And I must disagree on your opinion about Microcontrollers. A
>Microcontroller such as a PIC is unable to address memory, which equates
>to a large amount of code. And who has the equipment to program a PIC
>microcontroller? Other controllers, such as the Z182, used by one
>expander require more external circuitry, and is itself more powerful
>than the system it would be "serving".

Microcontroller's have TONS of advantages here.  First of all, they're
just one part compared to the many needed to interface to a serial or
parallel chip without one.  Second, they are easy to program once you
have the equipment.  Third, they are the cheapest alternative and
require the least amount of board space (you can get a relatively
powerful 16 pin microcontroller that could do the job for about $1.25
qty 1).  Fourth, they allow you to do FAR more important things such
as backup transferring, built-in file transferring intelligence,
better overwrite security, power management, etc.

What do you mean by "unable to address memory"?  

The controller I plan on using for the Expander III *is* more powerful
and tons faster than the Z80 inside the TI-85, and it's also much
faster than the 68k in the 92.  But that's not a bad thing!  Wait to
you see what this baby can do and you'll become a believer :).

>> And yes, the new expanders will probably still be using serial flash
>> EEPROM chips since they are convenient to access and have low
>> pincounts (these upcoming ones are cheaper, too).  Using a parallel
>> eeprom, while technically more prevalent in the semiconductor market,
>> are significantly more difficult to access because an 8Mbit parallel
>> EEPROM requires over 32 chip connections (8 data lines, 20 address
>> lines, minimum 4 control lines)!  That makes for a very complex
>> printed circuit board even with a microcontroller.
>
>Detailed/Computer aided design of the PCB can help keep the placement of
>parts simpler. 

Well, with parallel chips you're talking about routing as many as 50
traces to/from three to five different chips.  Not simple, not cheap,
and not worth it.  Also, the vast majority of parallel access flash or
EEPROMs are more expensive than their serial EEPROM counterpart (the
few that are available that is).

>I'm not really arguing for either side, they both have drawbacks, I'm
>just saying that Parallel FLASH chips can be used without the need for
>microcontrollers.

Of course they can, but the disadvantages of not using a
microcontroller FAR outweigh the advantages, as anyone who's
experienced with them will tell you.

-Mel
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-The TI-Memory Expansion Homepage
-http://www.egr.msu.edu/~tsaimelv/expander.htm
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