Retro Review: Texas Instruments TI55 III
I’m still in the 1980s mood, so today and for the next few
blog entries, I am going to work with the Texas Instruments TI55 III from the
mid 1980s. Anyone want to play Pac Man
or Super Mario Brothers?
TI55 III: Cost and
History
Years Made
19861987, the one I have is from 1987 made in Italy. This model was also made in Taiwan.
Cost
I purchased from Amazon for $23 including shipping. All the keys work and the display is in good
working order. The paint on the equals,
plus, minus, and multiplication keys are either completely or partially worn
off. However, everything works!
Original cost
From what I was able to research, about $40 to $50 (that is
an educated guess).
History
The TI55 III is based off of the original TI55 (1977) and
TI55 II (1981). The original TI55 had
only 32 programming steps but included 10 memory registers. When the TI55 II came out, the programming
memory was increased to 56 steps, but the number of memory registers were
slashed to 8. Furthermore, the total
memory competed with programming steps and memory registers. All bets were off if the statistics mode was
engaged. The TI55 II also added
integration.
Unfortunately, the TI55 II was plagued with bad keyboards,
which led Texas Instruments to replace it with the TI55 III (United States) or
the TI56 (foreign countries, mainly Europe).
The TI55 III retained all of the features of the TI55 II and received better
keyboards.
Rskey.org page on the TI55:
http://www.rskey.org/ti55
Datamath.org page on the TI55 II: http://www.datamath.org/Sci/Slanted/TI55II.htm
Datamath.org page on the TI55 III: http://www.datamath.org/Sci/Slanted/TI55III_TW.htm
Features of the TI55
III
Operating System: AOS
(Algebraic Operating System) (like the
TI30Xa)
Programming: Up to 56
program steps
Statistics: Linear
Regression
Conversions: °F/°C,
DMS/DD, in/cm, lb/kg, gal/L
Memory Registers: Up to 8, competed with both statistics and
programming
Other Functions:
Percent Change, Absolute Value, Signum, Integer Part, Fractional Part
Integration
Shift Keys: 2^{nd}, hyp, INV
Storage Arithmetic:
+, , *, ÷, ^, roots
Manual: Same as the
TI55 II. See the link above.
Oddities
Percent Key (Δ%)
I think the percent works backwards than modern calculators. Press
the new value first, then [2^{nd}] [ ) ] ( Δ% ), then old value, [ = ].
Example: Percent
change from 32 to 56: 56 [2^{nd}]
[ ) ] (Δ%) 32 [ = ] 75 (75% increase)
Combinations and Permutations
Maybe unique to this series is that combinations and
permutations are operated on a different format. These functions take one argument in the form of nnn.rrr.
Example:
Combination where n=15, r=2 is entered as 15.002 [2^{nd}]
[ 9 ] (nCr) (Result: 105)
Permutation where n=15, r=2 is entered as 15.002 [2^{nd}]
[ 8 ] (nPr) (Result: 210)
Decimal Settings
Fix: This is what it
says, fixed the number of the display to n places. To cancel, press [INV] [2^{nd}] [sin]
(Fix).
Engineering:
Engineering mode is executed with [2^{nd}] [EE] (Eng) or
sometimes when you enter large/small numbers requiring an exponent of 10. To cancel, press [INV] [2^{nd}] [EE]
(Eng).
Rectangular/Polar Conversion
[2^{nd}] [x<>y] (PR): to Rectangular. Input:
r [x<>y] θ [2^{nd}] [x<>y] (PR). Result: y [x<>y] x.
[INV] [2^{nd}] [x<>y] (PR): to Polar.
Input x [x<>y] y [INV] [2^{nd}] [x<>y] (PR). Result:
θ [x<>y] r.
This is similar to the TI65 and the original TI55.
Linear Regression
The model is y = ax + b.
To obtain a and b after entering the data, press [2^{nd}] [ * ] (b/a) for the intercept (b), then
[x<>y] for the slope (a).
Programming Model
The programming model for the TI55 III (and its
predecessors TI55 and TI55 II) are extremely simple. There are no loops other than the RST (which
sends the counter back to step 00 and stops execution). Everything is a straightforward calculation,
like a macro.
Also, the more memory registers you need, the less space you
have. You control the partition by the
sequence [2^{nd}] [LRN] (Part) n (where n is the number of registers
desired). Using all 8 registers (R0
through R7) eliminates the programming capability.
Partitions Chart
# of Registers

# of Programming
Steps Available

1 (R0)

56

2 (R0, R1)

48

3 (R0, R1, R2)

40

4 (R0, R1, R2, R3)

32

Each key is counted as step.
Yes, that includes the digits.
The only thing that is merged is anything combined with a [2^{nd}]
key press. The codes are straight forward,
they are two digit codes where the first digit is the row number (19) and the second
is the column number (15, for 2^{nd} functions 60). Statistics commands are not available in
programming.
Integration will require at least 3 registers. Functions are ended by [ = ] [ R/S ] [RST].
The lower limit is stored in R1, upper stored in R2, press [ ∫dx ],
number of intervals (up to 99), [R/S].
Source: Texas
Instruments. “TI55 II Scientific
Calculator Quick Reference Guide” 4^{th} Ed. 1984.
Final Verdict
The TI55 III is a nice basic calculator. If you were looking for an extensive
programming module, then you may be disappointed with this model since no loops
are offered and the space offered is scare.
Still, having the absolute value, sign, integer part, and fractional
part are pluses.
Despite the limitations, I am going to posts several
programs for the TI55 III in the nearby future.
Eddie
This blog is property of Edward Shore, 2016.