DATAMATH

DATAMATH CALCULATOR MUSEUM

Characterization of NEC Single-chip Calculator Circuits - µPD940 Series

The DCM-50A Platform supports the Characterization of many Non-TI single-chip calculator circuits with up to 42-pin packages using the DCM-50A Playground DIL42 Adapter mounted on top of the DCM-50A PG Frame Carrier with the voltages V_SS and V_DD/V_GG set to the appropriate levels.

µPD940

Device-under-Test:

• Package Markings Top: µPD940C H5728M
• Package Markings Bottom:
• Donor Calculator: Lloyd's Accumatic 30 (Model EH-9036, Type 255G), September 1975

Keyboard: The Lloyd's Accumatic 30 makes use of a keyboard assembly with 19 spring-supported plastic keys pushing small fingers on stamped sheet-metal pieces against contacts etched on a single-sided phenolic PCB. All switches are arranged in a 6*4 matrix with the rows connected to the SA-SF Outputs (Segment Scan) and the columns connected to the K0 to K3 Inputs (Keyboard Scan) of the µPD940 single-chip calculator circuit.

Keyboard Matrix of the Lloyd's Accumatic 30 (Model EH-9036, Type 255G):

	µPD940
	K0	K1	K2	K3
SA	CE	C
SB	=	%
SC	+	−	×	÷
SD	7	8	9
SE	3	4	5	6
SF	.	0	1	2

Display: The Lloyd's Accumatic 30 makes use of an 9-digit Futaba 9-CT-08 low-voltage Vacuum Fluorescent Display (VFD) connected directly to the respective 9 Digit Outputs D1 to D9 and 8 Segment Outputs SA to SG and SDP of the µPD940 and biased to approximately -28 Volts.

Display Layout:

Futaba 9-CT-08

The Segment drivers A-G and DP (Decimal Point) are connected to the Futaba 9-CT-08 display in the pictured way.

Display Fonts:

Type	Calculator	Number Fonts	Decimal Separator	Thousands Separator	Entry Overflow	Calculating Overflow	Minus
µPD940	Lloyd's Accumatic 30			n.a.

Keyboard Scanning: The µPD940 Series of single-chip calculator circuits utilizes six of its eight segment outputs to scan the keyboard after each display scanning cycle. Only the necessary digit-driver outputs are activated, when displaying a "0." only D1 would be enabled. The D10 to D12 Digit Times are used for keyboard scanning with the segment-driver outputs, while the display is blanked. The provided recording shows the moment the [=] key located in the keyboard scan matrix of segment output SB and keyboard input K0 was registered while displaying '1.'.

Display scanning: Display scanning is performed in D1 → D9 direction at a rate of about 1,040 Hz:

• State Time = 1 Clock = 0.020 ms @ CK=50 kHz
• Digit Time = 4 States = 0.080 ms @ CK=50 kHz
• Scan Time = 12 Digit Times (D1 to D9 with D10 to D12 a dead cycle) = 0.960 ms @ CK=50 kHz

µPD941

Device-under-Test:

• Package Markings Top: µPD941C H5X486
• Package Markings Bottom:
• Donor Calculator: MBO de Luxe I, December 1975

Keyboard: The MBO de Luxe I makes use of a keyboard assembly with 20 snap action switches and a sliding power switch soldered on a single-sided phenolic PCB. All switches are arranged in a 6*4 matrix with the rows connected to the SA-SF Outputs (Segment Scan) and the columns connected to the K0 to K3 Inputs (Keyboard Scan) of the µPD941 single-chip calculator circuit.

Keyboard Matrix of the MBO de Luxe I:

	µPD941
	K0	K1	K2	K3
SA	CE	C
SB	=	%		+/−
SC	+	−	×	÷
SD	7	8	9
SE	3	4	5	6
SF	.	0	1	2

Display: The MBO de Luxe I makes use of an 9-digit Itron DP95A4 low-voltage Vacuum Fluorescent Display (VFD) connected directly to the respective 9 Digit Outputs D1 to D9 and 8 Segment Outputs SA to SG and SDP of the µPD941 and biased to approximately -28 Volts.

Display Layout:

Itron DP95A4

The Segment drivers A-G and DP (Decimal Point) are connected to the Itron DP95A4 display in the pictured way.

Display Fonts:

Type	Calculator	Number Fonts	Decimal Separator	Thousands Separator	Entry Overflow	Calculating Overflow	Minus
µPD941	MBO de Luxe I			n.a.

• State Time = 1 Clock = 0.020 ms @ CK=50 kHz
• Digit Time = 4 States = 0.080 ms @ CK=50 kHz
• Scan Time = 12 Digit Times (D1 to D9 with D10 to D12 a dead cycle) = 0.960 ms @ CK=50 kHz

µPD943

Device-under-Test:

• Package Markings Top: µPD943C R5X096
• Package Markings Bottom:
• Donor Calculator: Royal 90K (Model UA120), November 1975

Keyboard: The Royal 90K (Model UA120) makes use of a keyboard assembly with a sliding power switch and 19 spring-supported plastic keys pushing small fingers on stamped sheet-metal pieces against contacts etched on a single-sided phenolic PCB. All switches are arranged in a 5*4 matrix with the rows connected to the SB-SF Outputs (Segment Scan) and the columns connected to the K0 to K3 Inputs (Keyboard Scan) of the µPD943 single-chip calculator circuit.

Keyboard Matrix of the Royal 90K (Model UA120):

	µPD941
	K0	K1	K2	K3
SA
SB	=	%	CI	C
SC	+	−	×	÷
SD	7	8	9
SE	3	4	5	6
SF	.	0	1	2

Display: The Royal 90K (Model UA120) makes use of an 9-digit Futaba 9-ST-10 low-voltage Vacuum Fluorescent Display (VFD) connected directly to the respective 9 Digit Outputs D1 to D9 and 8 Segment Outputs SA to SG and SDP of the µPD943 and biased to approximately -28 Volts.

Display Layout:

Futaba 9-ST-10

The Segment drivers A-G and DP (Decimal Point) are connected to the Futaba 9-ST-10 display in the pictured way.

Display Fonts:

Type	Calculator	Number Fonts	Decimal Separator	Thousands Separator	Entry Overflow	Calculating Overflow	Minus
µPD943	Royal 90K (UA120)			n.a.

• State Time = 1 Clock = 0.020 ms @ CK=50 kHz
• Digit Time = 4 States = 0.080 ms @ CK=50 kHz
• Scan Time = 12 Digit Times (D1 to D9 with D10 to D12 a dead cycle) = 0.960 ms @ CK=50 kHz

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