Old Calculator Web Museum Advertising and Documentation Archive
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
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.
Logic Schematic for Friden EC-130 Electronic Calculator
This document is presented as an embedded PDF. You may need to click above this text, or refresh the page for image to show, depending on your browser. If the document does not appear above, you may click
to download/view it on your PDF viewer program
If you don't have Adobe Acrobat Reader or some other form of PDF viewing
program, you may not be able to view this document.