DATAMATH CALCULATOR MUSEUM
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DATAMATH CALCULATOR MUSEUM |
Datamath Calculator Museum DCM-50A Playground Digit Inverter Frame Carrier
| Date of introduction: | April 21, 2025 | Display technology: | n.a. |
| New price: | Display size: | n.a. | |
| Size: | 3.2" x 4.0" x
0.45" 81 x 48 x 11 mm3 |
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| Weight: | 1.8 ounces, 50 grams | Serial No: | 0001 |
| Batteries: | n.a. | Date of manufacture: | mth 06 year 2025 |
| AC-Adapter: | n.a. | Origin of manufacture: | USA |
| Precision: | Integrated circuits: | CD4077 | |
| Memories: | |||
| Program steps: | Courtesy of: | Joerg Woerner |
The Datamath Calculator Museum
DCM-50A (PLAYGROUND) is based on the generic
DCM-50A
Platform to access most features of calculators and certain features of products other than
calculators that are not covered by the scope of the DCM-50A (TMS0100, TMS0800,
TMS1000, TMS1200 and TMS0900) and the DCM-50A
(OTHERS) category. It consists of different printed circuit boards
(PCBs) that can be stacked on top of the DCM-50A Platform:
| •
DCM-50A (PLAYGROUND) FRAME: Plug-In Carrier to access all voltages and signals
of the DCM-50A Platform • DCM-50A (PLAYGROUND) LED DD FRAME: Plug-In Carrier to access all voltages and signals of the DCM-50A Platform for Chips with LED Direct-Drive capability • DCM-50A (PLAYGROUND) DIGIT INVERTER FRAME: Plug-In Carrier to access all voltages and signals of the DCM-50A Platform for Chips with Inverted Inputs/Outputs • DCM-50A (PLAYGROUND) DIL42: Daughter Board with 42-pin ZIF Socket, Patch Field, Diode Matrices, Push Buttons, SPDT Switches and Pin-Modifiers • DCM-50A (PLAYGROUND) BB400: Daughter Board with Solderless Breadboard (400 connections), Push Buttons and SPDT Switches |
The
DCM-50A Platform was developed for single-chip calculator circuits with external
display drivers and consequently are digit drivers used for the Digit Outputs D1
to D11 and segment drivers used for the Segment Outputs SA to SH and SP. Most
calculator chips were manufactured in the early 1970s in PMOS (p-Channel MOS)
technology, meaning the output transistors are "high-side" switching and for the
so-called multiplexed common cathode LED displays in use with all LED-based
calculators, the digit drivers are "inverting" the polarity of the Digit
Outputs. Some early calculator chips and chipsets optimized for VF (Vacuum Fluorescent)
Displays are using "inverted logic" on their Inputs and Outputs, meaning an
active Digit Output disables the display, rendering them
incompatible with the DCM-50A Platform. To overcome this limitation,
incorporates the Digit Inverter Frame Carrier for each Digit Output a small
transistor to revert the polarity of the signals back. This modification of the
output signal polarity creates an issue with chip designs using the Digit
Outputs for keyboard scanning, consequently are optional inverters for the
keyboard scanning inputs available, too.
While reverse-engineering the original ALPHA chipset developed by Nortec Electronics for Omron famous Model 800 calculator, we observed an incompatibility of its unique keyboard scanning approach and modified the design of the DCM-50A (PLAYGROUND) DIGIT INVERTER FRAME slightly. The revised printed circuit board (PCB) replaces the CD4077 chip and white Switch to select between Non-Inverting or Inverting polarity of the four keyboard inputs KN, KO, KP and KQ with direct wires:
| • DCM-50A (PLAYGROUND) DIGIT INVERTER LITE FRAME: Plug-In Carrier to access all voltages and signals of the DCM-50A Platform for Chips with Inverted Inputs/Outputs |
To access all features of single-chip calculator circuits with Inverted Digit outputs, the schematics and layout of the DCM-50A Playground DIGIT INVERTER FRAME Carrier are providing accordingly:
| • VSS, VDD and VGG access from TMS0100 and TMS0800 Pin-Headers • Digit Outputs D1 (rightmost) to Digit Outputs D11 (leftmost) access from TMS0100 Pin-Headers with level-translators from the active-low high-side switching digit drivers to DCM-50A compatible active-high high-side switching digit drivers • Jumper-Header (black) to enable optional Digit Outputs D0 • Selectable pull-down voltage VDD and VGG for Digit Outputs D0 to D11 with Switch (red) • Segment Outputs SA to SH and SP from TMS0100 and TMS0800 Pin-Headers • Keyboard Inputs KN, KO, KP and KQ TMS0100 and TMS0800 Pin-Headers with Switch (white) to select Non-Inverting or Inverting polarity • TMS0100 CLK Oscillator from Jumper-Header J9 • Digital Discovery DIN0, DIN21 and DIN22 Signals from Jumper-Headers J10, J11 and J12, respectively • Digital Discovery DIO24 and DIO25 Signals from Jumper-Headers J9 and J13, respectively |
Please notice that the DCM-50A Playground Digit Inverter Frame Adapter needs to be plugged into the leftmost TMS0100 and center TMS0800 Pin-Headers on the DCM-50A Platform. It also connects to five Jumper-Headers on the DCM-50A Platform.
If you have additions to the above article please email: joerg@datamath.org.
© Joerg Woerner, December 7, 2025. No reprints without written permission.