The Museum of HP Calculators

HP-28C Features

Features in optional ROMs are listed as Option.
Features in HP mag card or tape Application Pacs are listed as +.
Other software is not included.
Display and Keyboard HP-28C
Display type LCD
Display format 4Line
FIXed number format Yes
SCIentific number format Yes
ENGineering number format Yes
STanDard / ALL number format Yes
Alpha messages and prompts Yes
Softkeys labeled by mag. card or overlay -
Softkeys labeled by display menus Yes
Softkeys with neither labeling system -
Status annunciators Yes
Redefinable keyboard -
Logic HP-28C
Logic system RPN/RPL
Stack levels Unlim
Last x Yes
Undo Yes
Precedence Yes
Parentheses Yes
Storage Addition (STO +) Yes
Storage Arithmetic (STO +, −, ×, ÷) Yes
Storage Exponentiation (STO ^) -
Recall Arithmetic -
Named variables Yes
Multiple data types Yes
Directories -
Math HP-28C
+, −, ×, ÷ Yes 
1/x Yes
x2 Yes
LOG x Yes
10x Yes
LN x Yes
ex Yes
yx Yes
π Yes
% Yes
% change Yes
INTeger truncation and ABSolute value Yes
Trigonometric functions (SIN, COS etc.) Yes
Hyperbolic trig. (SINH, COSH etc.) Yes
# of trig. modes (degrees, radians, grads) 2
Advanced Math HP-28C
Solver / root finder Yes
Numeric integration Yes
Complex numbers Yes
Matrix operations Yes
Matrix writer -
Equation writer -
Symbolic operations Yes
Fractions -
Plotting and graphics (display) Yes
Plotting and graphics (printer / plotter) Option
Statistical HP-28C
Mean, standard deviation (# of variables) Multiple
Σ of n, x, x2 -
Σ of n, x, x2, y -
Σ of n, x, x2, y, xy -
Σ of n, x, x2, y, y2, xy -
Σ of lists Yes
Random number generator Yes
Linear regression, estimate  Yes
Curve fitting -
Correlation coefficient Yes
Normal distribution Yes
Factorial Yes
Gamma Yes
Combinations and permutations Yes
Scientific and Time HP-28C
Polar / rectangular conversions Yes
Base conversions (2, 8, 10, 16) Yes
Arithmetic in bases 2, 8 and 16 Yes
Bit operations (AND, OR, XOR, ...) Yes
Selectable word size (1-64 bits) Yes
Selectable complement mode (1's, 2's, unsigned) -
Decimal hrs / hrs.min.sec. conversions Yes
Hrs.min.sec arithmetic Yes
Time of day clock -
Timer -
Dynamic calculations (timer × rate) -
Alarms -
Unit Conversions HP-28C
Centimeters / inches Yes
Millimeters / inches Yes
Meters / feet Yes
Kilograms / pounds (mass) Yes
Newtons / pounds (force) Yes
British thermal units / joules Yes
Liters / gallons Yes
° Celsius / ° Fahrenheit Yes
Other Yes
User-defined units Yes
Time Value of Money HP-28C
Number of payments (n) -
Interest rate (i) -
Present Value (PV) -
Payment (PMT) -
Future Value (FV) -
Cash Flow Analysis HP-28C
Net present value (NPV) -
Internal rate of return (IRR) -
Amortization HP-28C
Accumulated Interest (ACC INT) -
Balance (BAL) -
Depreciation HP-28C
Straight line (SL) -
Sum of the years digits (SOYD) -
Declining balance (DB) -
Bonds and calendar functions HP-28C
Bond price -
Bond yield -
Date arithmetic / calendar functions -
Memory and Programming HP-28C
Programming language(s) RPL
RAM / Max # of variables or addressable registers 2K Bytes
Max # of program steps Unlim
RAM / Max vars or regs with full optional RAM -
Max # of prog steps with full optional RAM -
Merged program steps  Yes
Manual register / program memory allocation  -
Automatic register / program memory allocation Yes
Overlapped register and program memory -
Continuous memory Yes
Flags 64
Conditional tests Many
Subroutine levels Unlim
Indexed looping (increment by +/- 1, end at 0) Yes
Indexed looping (choice of increment and end) Yes
Multiple index / loop registers Yes
Line number addressing -
Branching by relative line number -
Global program label addressing Yes
Local program label addressing Yes
Indirect / computed addressing and control Yes
Multiple indirection registers Yes
Pause Yes
Alpha messages and prompts in programs Yes
Alpha program listings Option
Alpha string manipulation Yes
Program step insert / delete Yes
I/O and Expansion Features HP-28C
ROM modules -
RAM modules or expansion option -
General expansion slots / connector -
Magnetic card reader/writer -
Tape drive -
Disk drive -
Upgradeable firmware -
Optical wand -
Serial port -
Infrared input -
Infrared output Yes
Printer Option
Networking -
Other -
General HP-28C
Sounds Yes
Self test Yes
Hard case (in addition to soft case) -
Additional Features -
Batteries 3 N cells
Length (inches) 6.2"
Width 3.75"
Height 0.7"
Weight (oz or lbs) 8oz
Year of introduction 1987
Features in optional ROMs are listed as Option.
Features in HP mag card or tape Application Pacs are listed as +.
Other software is not included.

Unlim means limited only by available memory.
HP-28C notes:
  • To start the self test, with the calculator on, press and hold ON and press ▼. The calculator will beep and display a series of vertical bars. You can now press any key to step through a series of tests (each with a different display - one blank.) Once the calculator displays KEYBOARD TEST, you must press each key on the alpha (left) keyboard starting from the upper left and proceeding from left to right and then down. You will hear a beep on each keystroke. After the alpha keyboard, do the same with the main (right) keyboard. When you are finished, you will see: OK-28C. The message FAIL will be displayed if there is a problem or if you press keys in the wrong order. By pressing and holding ON and pressing ◀, you can put the calculator into a continuous self-test (minus the keyboard test.) To exit the continuous test press and hold ON and press the ▲ key.

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