DATAMATH

DATAMATH CALCULATOR MUSEUM

Datamath Calculator Museum DCM-50A Digit Blank Adapter

Date of introduction:	September 21, 2022	Display technology:	n.a.
New price:		Display size:	n.a.
Size:	2.0" x 2.2" x 0.80" 51 x 56 x 20 mm³
Weight:	0.7 ounces, 20 grams	Serial No:	0001
Batteries:	n.a.	Date of manufacture:	mth 01 year 2023
AC-Adapter:	n.a.	Origin of manufacture:	USA
Precision:		Integrated circuits:	2*SN75494, CD4077
Memories:
Program steps:		Courtesy of:	Joerg Woerner

The Datamath Calculator Museum DCM-50A Platform offers a lot of flexibility to access the features of calculators based on Texas Instruments’ single-chip calculator circuits but is centered around a 12-digit single-line LED display. This Digit Blanking Adapter supports the Characterization of the TMC1079 chip used in the Canon MD-8, the World's first pocket calculator with a two-line Vacuum Fluorescent Display (VFD).

A novel layout of the 20-digit VFD allows the TMC1079 to fully control it with the available 11 R Outputs (Display Scan) and 8 O Outputs (Segments): All Anodes of the VFD are connected in the usual way to the 8 O Outputs and the 10 Grid-Pairs are connected directly to the R0 to R9 Outputs of the TMC1079 and biased to approximately -30 Volts with discrete pull-down resistors. Display Scan Output R10 is used to "multiplex" between the upper line (R10 active) and lower line (R10 inactive) of the display by lifting the corresponding Filament supply above a certain threshold. An additional patch wire connecting Pin 3 (R10 Output) of the TMS1000 socket and the "Blank" Input of the Digit Blank Adapter allows to simulate this behavior with the DCM-50A Platform by selecting the desired display line with the yellow push button on the printed circuit board (PCB).

The design of the Digit Blank Adapter allows with two separate inputs to activate and deactivate the two display drivers for D1 to D5 and D6 to D11 individually, allowing to simulate the implementation of Texas Instruments' "12^th digit" introduced with the SR-10 (TMS0120) and used with the SR-11 (TMS0602), too.

One additional feature of the Digit Blank Adapter is an optional "Inverter" for each of the two Blanking inputs of the SN75494 display drivers to enhance its flexibility.

The schematics and layout of the Digit Blanking Adapter are providing accordingly:

• Connecting pins to the DCM-50A Platform Digit Driver sockets
• Two SN75494 Digit Drivers
• Two inputs for individual Blanking of D1 to D5 or D6 to D11 with jumper field to shunt the inputs together
• Jumper field to optionally invert the Blanking signals of the SN75494 Digit Drivers
• Yellow push button to select active display line

Please notice that the Digit Blank Adapter needs to be plugged into the two SN75494 Digit Driver sockets on the DCM-50A Platform.

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