Texas Instruments TI-53

Datasheet legend
Ab/c: Fractions calculation
AC: Alternating current
BaseN: Number base calculations
Card: Magnetic card storage
Cmem: Continuous memory
Cond: Conditional execution
Const: Scientific constants
Cplx: Complex number arithmetic
DC: Direct current
Eqlib: Equation library
Exp: Exponential/logarithmic functions
Fin: Financial functions
Grph: Graphing capability
Hyp: Hyperbolic functions
Ind: Indirect addressing
Intg: Numerical integration
Jump: Unconditional jump (GOTO)
Lbl: Program labels
LCD: Liquid Crystal Display
LED: Light-Emitting Diode
Li-ion: Lithium-ion rechargeable battery
Lreg: Linear regression (2-variable statistics)
mA: Milliamperes of current
Mtrx: Matrix support
NiCd: Nickel-Cadmium rechargeable battery
NiMH: Nickel-metal-hydrite rechargeable battery
Prnt: Printer
RTC: Real-time clock
Sdev: Standard deviation (1-variable statistics)
Solv: Equation solver
Subr: Subroutine call capability
Symb: Symbolic computing
Tape: Magnetic tape storage
Trig: Trigonometric functions
Units: Unit conversions
VAC: Volts AC
VDC: Volts DC
Years of production:   Display type: Numeric display  
New price:   Display color: Black  
    Display technology: Liquid crystal display 
Size: 6"×3"×½" Display size: 8(5+2) digits
Weight: 4 oz    
    Entry method: Algebraic with precedence 
Batteries: 2×"LR44" button cell Advanced functions: Trig Exp Cmem 
External power:   Memory functions:
    Programming model: Keystroke entry 
Precision: 11 digits Program functions:  
Memories: 1 numbers Program display:  
Program memory: 32 program steps Program editing:  
Chipset:   Forensic result: 9.177087088  

ti53.jpg (22599 bytes)Were it that the Litronix 2290 didn't exist, the TI-53 would surely win an award as the least functional programmable calculator ever made (okay, I'm being unfair. There were some impressively dysfunctional machines made by Sinclair, too.) 32 program steps, only one memory register, no control transfer or conditional instructions... not a heck of a lot you can do with this beast! It's worse than the TI-55, which I thought of, until I received this TI-53, as the least programmable "almost programmable" calculator Texas Instruments ever made. To add insult to injury: they actually placed the word "programmable" on this calculator's faceplate, something they didn't dare to do with the TI-55.

The programming model of the TI-53 has some peculiar differences from the programming model of most TI calculators. It is the only TI calculator I know of on which the keycodes for the number keys are not the numeric values of the keys but represent their keyboard positions. The code 00 (the default with which program memory is filled on power-up) does not represent a valid instruction and causes an error when executed. The INV key also doubles as the 2nd (second function) key but it's not merged with the next keystroke, making program memory even more limited.

No room to build a Gamma function program on this beast, of course. Here is, instead, a program that implements Stirling's approximation of the factorial:

00 41    STO
01 55    ×
02 73    2
03 55    ×
04 42    π
05 85    =
06 13    √
07 55    ×
08 51    RCL
09 35    yx
10 51    RCL
11 45    ÷
12 51    RCL
13 31    INV
14 34    lnx
15 55    ×
16 43    (
17 51    RCL
18 11    1/x
19 45    ÷
20 72    1
21 73    2
22 75    +
23 72    1
24 85    =
25 81    R/S
26 31    INV
27 81    RST