Re: TI-92 processor
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The TI-92 is not a fast calculator despite its processor. For
numerical calculations it is slower than e.g. TI-85. I also don't
understand why the calculator gradually slows down more than 10%
when the history file grows. The time for inverting an (N*N) integer
matrix grows as N^3 for approximative calculations and almost as N^4
for exact calculations. This can be symptoms of ineffective memory
management when the memory fills up. There are also some doubts that
it really runs at 10 MHz (is this REALLY confirmed by TI). I got the
information from David Ellsworth (the guy who struggles with Fargo)
that he had clocked an own assembly program in RAM to 5 MHz. The
processor is called SC414181FG16 and is custom made for Texas
Instruments. It is probably something like a low power version of
68008 for 8 bit external memory. The power consumption of the TI-92
is amazingly low, I measure only 4.5-7 mA when waiting for input and
35-45 mA when doing calculations depending on battery voltage
(4.5-6V).
David Ellsworth has found a code snippet in ROM of the TI-92
Operating System that automatically detects the RAM-size. Since the
RAM-chip that is used is commersially available from Toshiba this
looked rather promising so I opened the calculator but there is no
longer any extra space for another 128k chip. The circuit board
seems to have been revisioned lately (I have version 1.11 from
04/11/96) and the component layout changed. The old layout where
there seems to be provisions for an extra RAM-chip can be found on
the net on George Nachmans page
http://www.wam.umd.edu/~ltduck/ti92/hacking.html
The integrated circuits are still the same, except that I think my
memory was TC551001BFL-85L and not
TC551001BFTL-85L (change of package?). But the layout is different,
both T6A40 are located vertically to the left side. The three T6A39
are placed in a straight row on the top, the processor and the RAM
are still on approximatively the same positions on the right side
BUT THERE IS NO SPACE FOR EXTRA MEMORY. Inbetween the PCB contacts
for the ROM module there are solder tabs for a 44-pin circuit but I
don't think that is for extra RAM. It is more probably a provision
for making the ROM permanent in future versions. I don't know if
these solder tabs existed in the previous PCB layout.
Despite the fact that the TI-92 is surprisingly slow it is quite
powerful on symbolic algebra. It is also very user friendly
(compared to HP-48G) with its fairly big screen and QWERTY keyboard.
I have good use of it in my research work and think it is well worth
the money.
Richard Schatz, Ph.D.
Laboratory of Photonics and microwave Engineering
Royal Institute of Technology
Stockholm
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