Compucorp 324G Scientist

The Compucorp 324G could be called the best engineered calculator of its time. Introduced in the year 1972 the 300-line from Computer Design Corporation (CDC) were far ahead of their time. CDC, Los Angeles designed an universal data-processor with external ROM's for the operating system and mathematical functions and external RAM for data- and program-storage. 

A lot of different calculators appeared in the neat 300-Series housing, like the Scientist models 320G, 322G and this 324G:

Don't miss the wonderful web-sites of Rick Bensene and Viktor T. Toth to get an impression of the remaining models for financial or statistical operations. In Japan this calculator was sold by RICOH as RICOMAC X-822.

Even calculators in a much larger desktop housing with integrated printer were introduced between 1972 and 1974: 

The integrates circuits of the 300-line were originally manufactured by AMI, later TI was chosen as a reliable second source. Please use the thumbnails below to get a deeper look inside the wonderful Compucorp 324G.

The Compucorp 324G uses a high quality keyboard with a tactile and audible feedback. Please notice that the upper row includs some switches not accessible through the keyboard plate. They seem to be used on other models of the Compucorp 300 line. The very similar 320G and 322G are missing even more switches.

The display of the Compucorp 324G is a 16-digit Panaplex II style manufactured by Burroughs in the United States. We know this display from early Texas Instruments calculators like the SR-20.

The brain of the Compucorp 324G uses a stack of 4 printed circuit boards (PCBs). The top PCB scans the keyboard and the display with the TMC1869 and TMC1884 circuits. Some discrete transistors and Integrated Circuits (ICs) drive the high voltage of the Panaplex II display.

The second PCB of the 324G assembles the processing unit of the Compucorp 300-line calculators. A total of four ICs is used. They are numbered TMC1866, TMC1867, TMC1870 and TMC1872. The four chips together feature a ROM programmable unit, we know this approach from later products like the Texas Instruments SR-52.

The third PCB of the stack gives the 324G its identity as a programmable calculator for scientists: Beside the TMC1871 interface circuit to the memory we notice: Three ROM (Read Only Memory) for program storage of the calculator operating system and four RAM (Random Access Memory) to store both data and user programs.

The forth and last PCB of the calculator gives an universal power supply to generate the different voltages in the calculator. The calculator itself uses either 4 D-size batteries or an external converter.

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

© Joerg Woerner, December 5, 2001. No reprints without written permission.