Hewlett-Packard HP-45

Hewlett-Packard introduced in January 1972 the World's first pocket sized electronic calculator performing both logarithmic and trigonometric functions, simply named as Model 35 or HP-35 as reference to its number of keys. With the fast progress in the semiconductor industry, it took HP about one year before they could more than double the program memory of the HP-35 architecture and even add an extra data memory chip into the compact calculator housing, allowing the addition of multiple features for the HP-45 "Advanced Scientific" calculator:

To access the additional functionality of the HP-45, Hewlett-Packard added a yellow [2^nd] key, maintaining a keyboard layout with just 35 keys.

And Hewlett-Packard could enjoy again their first-mover advantage, it took exactly 2 years from the introduction of the HP-35 before Texas Instruments launched in January 1974 their competing SR-50 Slide Rule calculator and almost 2 years between the HP-45 release and TI's SR-51.

Dismantling the featured HP-45 manufactured in December 1973 (or February 1974) in the United States reveals immediately the legendary build quality of Hewlett-Packard's Test and Measurement equipment and we couldn't discover a single instance where bean-counters ruled engineers. Starting with more than a dozen of hidden screws to hold the calculator together, the gold-plated traces of the printed circuit boards (PCBs), gold plated connectors and keyboard contacts and ending with the mechanism to lock the battery cover with sliding rubber feet and the 3-pin power supply connector locking the battery cover - the HP-45 is like the HP-35 a marvel of engineering!

The internal design of the HP-45 is based on a stack of two PCBs, separated with a plastic frame and electrically connected with a 25-pin connector. The Main PCB contains the calculator brain, power supply and a clock driver while the Keyboard and Display PCB includes the contacts for the 35 keys and On-Off switch, the display drivers and the 7-Segment LED display with 15 digits. The calculator is powered by a HP-82001A battery pack with three AA-sized NiCd batteries that can be easily replaced.

Hewlett-Packard designed the functional logic of all Integrated Circuits of the HP-45 but outsourced the development, manufacturing, testing and packaging of the five PMOS chips of the calculator brain to both Mostek Corporation in Carrolton, TX and American Microsystems, Inc (AMI) in Santa Clara, CA. The various ICs from Mostek and AMI are different from the implementation but interchangeable in the calculator and we located in the featured HP-45 a mix of both suppliers. The CPU of the HP-45 is based on a Serial 1-bit architecture with 56-bit Registers and divided into two chips.

The first chip is called Arithmetic and Register (A&R) Circuit and includes the Instruction Decoder, Adder, Masking-logic for the operands, Registers and Display Decoder. The A&R Chip of the featured calculator was manufactured by Mostek and uses not only HP's 1820-1169 part number but Mostek's MK6020P designation, too. Its date code of 7401 (January 1974) suggest that Hewlett-Packard used the calculator Date code 1350A38640 (year 1960+13 week 50, USA) not strictly as a reference to its exact manufacturing date but an indicator to the Revision of the calculators manufactured. Other Date codes located inside the featured calculator suggest an actual manufacturing date in February 1974. The second chip, called Control and Timing (C&T) Circuit, includes Address Register, Address Calculation for Branches, Page Decoder and Subroutine Return Address for the external ROM and 12 Status Bits. The C&T Chip of the featured calculator was manufactured by AMI and is marked with 1818-0078 and a date code of 7349, matching the calculator manufacturing date.

e program of the HP-45 is stored in two "Quad" Read-Only Memories (ROMs) with a capacity of 1,024*10 bits, each. The program of the HP-45 is stored in two "Quad" Read-Only Memories (ROMs) with a capacity of 1,024*10 bits, each. While the HP-35 uses three ROMs with a capacity of 256*10 bits, each housed in 10-pin TO99 Metal can packages and the HP-80 uses seven of these chips directly bonded on a ceramic substrate of a hybrid package and protected with a metal lid, opted Hewlett-Packard for the HP-45 to use standard 16-pin ceramic freeing some real estate on the PCB for the additional Register Chip. The two Quad ROMs of the featured calculator are manufactured by AMI and marked with HP 1818-0057 and HP 1818-0082, respectively. The ten additional Data Registers of the HP-45 are realized with the HP 1820-0993 RAM (Random-Access Memory) with a capacity of 10*56 bits. The RAM chip of the featured HP-45 was manufactured by Mostek and sports a MK6036P marking, too. The HP 1820-1128 Clock Driver and Reset Chip converts the two-phase clock generated by the Anode Driver and System Clock Chip located on the Keyboard and Display PCB to appropriate voltage levels for the PMOS chips of the calculator brain and initialized the circuits after power on.

The Keyboard and Display PCB uses most of its real estate for the contacts of the 35 keys and the On-Off Switch but contains both the 15-digit LED Display and its drivers, too. The LED Display is assembled with 3 HP 1990-0335 5-digit 7-Segment LED Modules operated in a multiplexed mode.

The main clock of the HP-45 is generated by the HP 1820-1029 Anode Driver and System Clock Chip and the HP 1820-1061 and Display Scanning and Cathode Driver Chip is generating the multiplexing signals. Both chips in concert drive the Anodes respectively Cathodes of the 7-Segment Display.

Learn more about Mostek Calculator Integrated Circuits.

Milestones of HP calculators

Hewlett-Packard (HP) introduced in 1968 the World's first desktop scientific calculator, the HP 9100A. The programmable calculator stores programs on magnetic cards and lets scientists perform complex calculations without the need to access much larger computers. It is 10 times faster than most machines at solving science and engineering problems. Advertisements for the 9100A call the device a "personal computer," one of the first documented uses of the term.

Only 4 years later, on January 4, 1972, HP makes another advance in personal computing with the HP-35, the World's first scientific handheld calculator. Small enough to fit into a shirt pocket, the powerful HP-35 makes the engineer's slide rule obsolete. With the HP-80 a similar business model was introduced in February 1, 1973. In May of 1973 the HP-45 followed before the first programmable model HP-65 was introduced in January 19, 1974 with a retail price of $795. The HP-70 was introduced in August 1974 to complement the HP-80 as lower end business calculator and it took another few months till the introduction of the HP-55 in January 1975, the last calculator in Hewlett-Packard's series of "First Generation Handheld Calculators". Early in the year 1975 the price tag of the HP-35 dropped to $195 and the calculator was discontinued soon after with the introduction of its successor HP-21, a member of the "Second Generation Handheld Calculators". The introduction of the HP-31E in May 1978 together with its siblings HP-33E and HP-38E marked with the "Third Generation of Handheld Calculators" the end of HP calculators with LED Displays before introducing the revolutionary HP-41C with its alphanumeric LC-Display in July 1979 and the everlasting HP-12C and its sibling HP-11C in September 1981.

In the year 1975 dozens of companies manufactured calculators with 4 functions and a selling price below $20, scientific and business calculators in the range around $100 and programmable calculators priced about $250. The slide rule was outdated and famous companies like Dennert & Pape (ARISTO), A.W. Faber-Castell and Keuffel & Esser stopped the production.

If you have additions to the above article please email: joerg@datamath.org.

© Joerg Woerner, October 22, 2023. No reprints without written permission.