DATAMATH

DATAMATH CALCULATOR MUSEUM

Datamath Calculator Museum DCM-50A Playground KBD123 Keyboard with Switch Matrix

Date of introduction:	November 18, 2024	Display technology:	n.a.
New price:		Display size:	n.a.
Size:	3.5" x 7.5" x 0.45" 89 x 191 x 12 mm³
Weight:	3.2 ounces, 91 grams	Serial No:	0001
Batteries:	n.a.	Date of manufacture:	mth 11 year 2024
AC-Adapter:	n.a.	Origin of manufacture:	USA
Precision:		Integrated circuits:
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 from the DCM-50A Platform
• 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

While these additions greatly enhance the flexibility of the DCM-50A Platform, is it still hampered by its keyboard design. Designed for compatibility with Texas Instruments single-chip calculator circuit introduced between 1971 and 1975, does it provide the following means to emulate a calculator keyboard:

• 11x4 switch matrix keyboard with patch field for SPST switches (e.g. Constant/Chain) or selector switches (e.g. F/4/2) with diode matrix
• Jumper field to select between digit scanning (D1 to D11) or segment scanning (SA to SG, SDP) of the keyboard
• Jumper to route D10 from TMS0100 and TMS1000 or DK from TMS0800 to keyboard column 10

Most Non-TI single-chip calculator circuits are covered by these specifications, but some manufacturers chose different approaches:

• Mostek's MK50310 Series uses an additional digit output D0 for scanning of a 12 x 3 keyboard matrix
• NEC's µPD946 Series uses an additional segment output SH and a V_SS column for scanning a 10 x 3 keyboard matrix and selector switches
• And we do not talk about General Instrument's GI 250, Mostek's MK6010 or NEC's µPD271 - they go with the DCM-50A (PLAYGROUND) KBD102

To overcome some of the limitations of the DCM-50A keyboard, we developed here at the Datamath Calculator Museum the DCM50A Playground KBD123 Keyboard with Switch Matrix. It is plugged on top of the DCM-50A Platform and centered around a 12x3 switch matrix keyboard with patch field for selector switches with diode matrix. All pins of the matrix (12 columns, 3 keyboard rows and 1 switch row) are directly accessible on pin headers and can be connected with the matching pins on the DCM50A PG DIL42 or DCM50A PG BB400 Daughter Boards.

Please notice that the DCM-50A Playground KBD123 Keyboard needs to be plugged into the switch matrix connectors on the DCM-50A Platform for proper alignment. It also connects to the keyboard stimuli signals KN, KO, KP, and KQ from the Digilent Discovery for debug purposes.

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