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Characterization of CT5001 Family Single-chip Calculator Circuits

The DCM-50A (PLAYGROUND) supports the Characterization of the CT5001 Family single-chip calculator circuits using the DCM-50A Playground MK6010 Adapter mounted on top of the DCM-50A PG Digit Inverter Frame Carrier and supported by the DCM-50A PG KBD102 Keyboard configured to MK6010 Mode. The voltage selector jumper on the MK6010 Adapter must be set to the appropriate voltage. The optional DCM-50A Playground Digilent I/O Extender supports Characterization and Reverse-engineering of CT5001 Family single-chip calculator circuits.

CT5001

Device-under-Test:

Keyboard: The Unitrex 1200 makes use of a keyboard assembly with 17 spring-loaded plastic keys pushing two fingers of stamped sheet-metal pieces soldered perpendicular on a single-sided phenolic PCB together. The 10 number keys are connected with a diode matrix to the key inputs KN1 to KN4 (Numbers) of the CT5001 while the 7 function keys are connected to its discrete key inputs. The 4-position sliding switch for the Decimal Point selection is connected with a diode matrix to the DP1 and DP2 inputs of the CT5001.

Keyboard Matrix of the Unitrex 1200 (Type 27, Rev. 4C):

	CT5001
KEY	KN8	KN4	KN2	KN1
[1]	-	-	-	log.1
[2]	-	-	log.1	-
[3]	-	-	log.1	log.1
[4]	-	log.1	-	-
[5]	-	log.1	-	log.1
[6]	-	log.1	log.1	-
[7]	-	log.1	log.1	log.1
[8]	log.1	-	-	-
[9]	log.1	-	-	log.1
[0]	log.1	-	log.1	-

Display: The Unitrex 1200 makes use of a USHIO U-BR-12400ES Planar Neon Gas Discharge Display (Panaplex-style) connected with two Kyodo KH-6225 Digit Driver Modules and 12 high-voltage capacitors as level shifters to the twelve Digit Outputs D1 to D12 of the CT5001 and one Kyodo KH-6259 Segment Driver Module connected to the Segment Outputs SA to SG and SDP of the CT5001. The display is operated with approximately +180 Volts. An additional discrete orange miniature gas-discharge lamp is used as minus sign for negative numbers and connected with a transistor to the Sign output of the CT5001.

Display Layout:

USHIO U-BR-12400ES plus Lamp

The Segment drivers A-G and DP (Decimal Point) are connected to the USHIO U-BR-12400ES display in the pictured way.

Display Fonts:

Type	Calculator	Number Fonts	Decimal Separator	Thousands Separator	Entry Overflow	Calculating Overflow	Minus
CT5001	Unitrex 1200 (Type 27)			n.a.

Display scanning: The CT5001 single-chip calculator circuit is manufactured in a PMOS process and its Digit Scanning Outputs are high-side PMOS transistors. For easy interfacing to low-voltage VFDs (Vacuum Fluorescent Displays) or high-voltage gas-discharge displays, an activated digit corresponds to a logical 0 or open output. All other, non-activated digits have the PMOS transistors turned on. Please notice that the the DCM-50A PG Digit Inverter Frame Carrier used to characterize the CT5001 chip is inverting the Digit Outputs D1 to D12 and we labeled them therefore /D1 to /D12 on the graphs.

Display scanning is performed in D1 → D12 direction at a rate of about 480 Hz:

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

© Joerg Woerner, April 5, 2026. No reprints without written permission.