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Logic Schematic for "Four-Counter" version of the EC-130 Calculator
Fall, 1964

This is a logic-level block diagram for the Four-Counter version of Friden's first electronic calculator, the Friden EC-130. The Four-Counter version of the EC-130 was an early implementation, with the initial production of the EC-130 calculators containing four 5-bit counters. A design change in the middle part of 1965 resulted in an improvement to the logic that eliminated the B counter, simplifying the machine, and reducing manufacturing cost. The change to the Three-Counter architecture begain with EC-130's with serial #8500. The Three-Counter EC-130 Logic Schematic is also available.

There is no date listed on this document, but given that this logic schematic appears to have been generated as an "as-built" document based on a production Friden EC-130 calculator with a serial number of 1016, it seems likely that it was created sometime in the fall of 1964.

The logic block diagram includes all of the logic elements of the calculator at the gate and flip-flop level. The schematic includes only the logic circuitry located on the plug-in circuit boards, and does not include the power supply, details of the write driver and read amplifier for the delay line, as well as details of aspects of the CRT drive and deflection circuitry. Details of these circuits can be found in the Service Manual.

Given that the EC-130's logic is implemented entirely with discrete components the schematic uses unusual symbology and nomenclature to designate the logic elements. The general logic function is the OR gate, which is shown in the schematic as a box with an "O" at the top center. Boxes with an "I" in the top center are inverters. Boxes with an "A" designation are AND gates, and boxes with "EF" are transistor emitter follower circuits, used on the output of gates to allow higher fanout capacity for gates that need to drive many other gate inputs. Boxes that are divided in half by a horizontal line represent flip flops. Some flip flops have "EF" designations on their outputs, indicating that the outputs use an emitter follower to provide higher fanout for driving other logic. Other small boxes with diamond-shaped symbols on inputs are called AC gates, which operate on logic level transitions rather high or low states. The logic design is well described in the EC-130 Service Manual, with some additional information in the EC-130 Field Service Manual.

This schematic can be used in conjunction with the Four Counter Friden 130 Master Design Document (MDD, also called the Computer Printout) to determine the actual components used for each logic element.

Any re-distribution of this document, printed or electronic, must include the watermark indicating its source as the Old Calculator Museum. Thank you.

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Logic Schematic for Friden EC-130 Electronic Calculator
Fall, 1964

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