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Characterization of Single-chip Calculator Circuits - TMS0100 Family

The DCM-50A Platform supports the Characterization of TMS0100 Devices including TMS1802 and TMS1875 in its left-most TMS0100 Textool Test Socket with the voltages VSS set to 7.2V and VGG set to -7.2V, accordingly.

TMS1875NC

Device-under-Test:

Package Markings Top: TMS1875NC, 7227
Package Markings Bottom: 11983
Donor Calculator: Heathkit IC-2008, March 1972

Keyboard: The Heathkit IC-2008 makes use of a keyboard assembled with individual long-stroke push-button switches arranged in an 11*2 matrix with the rows connected to the D1-D11 Outputs (Display Scan) and the columns connected to the KN (Keyboard Scan Numerical) and KO (Keyboard Scan Operational) Inputs of the TMS1875NC single-chip calculator circuit. The thumb-wheel switch to select the position of the decimal point is connected between the D1-D7 and D10 Output and KP (Keyboard Scan Decimal Point) Input while the latching push-button switch for the Constant Mode is connected between the D10 Output and KQ (Keyboard Scan Constant) Input.

Keyboard Matrix of the Heathkit IC-2008:

 

TMS1875

  KN KO KP KQ
D1 1 + [F-DP1]  
D2 2 × [F-DP2]  
D3 3 ÷ [F-DP3]  
D4 4 [F-DP4]  
D5 5   [F-DP5]  
D6 6   [F-DP6]  
D7 7 +/− [F-DP7]  
D8 8 =    
D9 9 .    
D10 0 CE [F-DP0] [C-K]
D11   C    

Display: The Heathkit IC-2008 makes use of a 9-digit display assembly with three 3-digit Sperry SP-753 planar neon gas discharge "Panaplex II" display modules. The nine discrete high-voltage drivers for the Anodes of the display assembly are connected to the D1-D8 and D11 Outputs (Display Scan) of the TMS1875NC and the 8 discrete high-voltage drivers for the Cathodes to its SA-SG and SP Outputs (Segments) with SH not connected. An additional flip-flop with its clock input connected to the Digit Driver output D11 of the TMS1875NC used for the left-most digit and its two Q and /Q outputs connected to the eight discrete high-voltage drivers. This circuitry changes the pre-programmed scanning order of the TMS1875NC from D11→D10→D9D1 to D11→D10→D8...D2 / D11→D9→D7D1 (with D10 and D9 actually not used for the display of an 8-digit calculator), an implementation of the "Interlaced Scan Multiplex Operation" recommended for multiplex operation of SP-700 series displays. The advantage of this approach is that the blanking time normally required within a display envelope to avoid "ghosting" is accomplished while other display envelopes are addressed. The left-most 3-digit Sperry SP-753 display module of the IC-2008 calculator would see a D11→D8 / D11→D7 scanning order, the middle display module a D6→D4 / D5 scanning order, and the right-most display module a D2 / D3→D1 scanning order, fulfilling the 150 us blanking time requirement of the SP-700 Series. The voltage swing for the Anodes and Cathodes of the evaluated Heathkit IC-2008 calculator manufactured in March 1972 was measured with about 80/120 Volts to 220 Volts.

Display Layout:

3*SP-753

The Output Decoder PLA of the TMS1875NC is programmed for 7-Segment displays with the following Output Assignments:

TMS1875 Pin 16 17 18 19 20 21 22 23 24
TMS1875 Port SA SB SC SD SE SF SG (SH) SP
Segment A B C D E F G   DP
The Segment drivers A-G and DP (Decimal Point) are connected to the Sperry SP-753 display assembly in the pictured way. Segment H is always active and not used. 

Display Fonts:

Type Calculator Number Fonts Decimal
Separator
Entry
Overflow
Calculating
Overflow
Minus Segment H
TMS1875NC Heathkit
IC-2008
    active

Scanning: Display and keyboard scanning is performed in D11 → D1 direction at a rate of about 584 Hz with the Digits blanked at State S1 and State S13 but no Segment blanking:

State Time = 3 Clocks = 0.012 ms @ CK=250 kHz
Digit Time = 13 States (1 Instruction Cycle) = 0.156 ms @ CK=250 kHz
Scan Time = 11 Digit Times (D1 to D11) = 1.712 ms @ CK=250 kHz

TMS0101NC

Device-under-Test:

Package Markings Top: TMS0101NC, A7215
Package Markings Bottom: 30038
Donor Calculator: Heathkit IC-2008A, May 1972

Keyboard: The Heathkit IC-2008A makes use of a keyboard assembled with individual long-stroke push-button switches arranged in an 11*2 matrix with the rows connected to the D1-D11 Outputs (Display Scan) and the columns connected to the KN (Keyboard Scan Numerical) and KO (Keyboard Scan Operational) Inputs of the TMS0101NC single-chip calculator circuit. The thumb-wheel switch to select the position of the decimal point is connected between the D1-D7 and D10 Output and KP (Keyboard Scan Decimal Point) Input while the latching push-button switch for the Constant Mode is connected between the D10 Output and KQ (Keyboard Scan Constant) Input.

Keyboard Matrix of the Heathkit IC-2008A:

 

TMS0101

  KN KO KP KQ
D1 1 + [F-DP1]  
D2 2 × [F-DP2]  
D3 3 ÷ [F-DP3]  
D4 4 [F-DP4]  
D5 5   [F-DP5]  
D6 6   [F-DP6]  
D7 7 +/− [F-DP7]  
D8 8 =    
D9 9 .    
D10 0 CE [F-DP0] [C-K]
D11   C    

Display: The Heathkit IC-2008A makes use of a 9-digit display assembly with three 3-digit Sperry SP-753 planar neon gas discharge "Panaplex II" display modules. The nine discrete high-voltage drivers for the Anodes of the display assembly are connected to the D1-D8 and D11 Outputs (Display Scan) of the TMS0101NC and the 8 discrete high-voltage drivers for the Cathodes to its SA-SG and SP Outputs (Segments) with SH not connected. An additional flip-flop with its clock input connected to the Digit Driver output D11 of the TMS0101NC used for the left-most digit and its two Q and /Q outputs connected to the eight discrete high-voltage drivers. This circuitry changes the pre-programmed scanning order of the TMS0101NC from D11→D10→D9D1 to D11→D10→D8...D2 / D11→D9→D7D1 (with D10 and D9 actually not used for the display of an 8-digit calculator), an implementation of the "Interlaced Scan Multiplex Operation" recommended for multiplex operation of SP-700 series displays. The advantage of this approach is that the blanking time normally required within a display envelope to avoid "ghosting" is accomplished while other display envelopes are addressed. The left-most 3-digit Sperry SP-753 display module of the IC-2008A calculator would see a D11→D8 / D11→D7 scanning order, the middle display module a D6→D4 / D5 scanning order, and the right-most display module a D2 / D3→D1 scanning order, fulfilling the 150 us blanking time requirement of the SP-700 Series. The voltage swing for the Anodes and Cathodes of the evaluated Heathkit IC-2008A calculator manufactured in May 1972 was measured with about 80/120 Volts to 220 Volts.

Display Layout:

3*SP-753

The Output Decoder PLA of the TMS0101NC is programmed for 7-Segment displays with the following Output Assignments:

TMS0101 Pin 16 17 18 19 20 21 22 23 24
TMS0101 Port SA SB SC SD SE SF SG SH SP
Segment A B C D E F G   DP
The Segment drivers A-G and DP (Decimal Point) are connected to the Sperry SP-753 display assembly in the pictured way. Segment H is not used. 

Display Fonts:

Type Calculator Number Fonts Decimal
Separator
Entry
Overflow
Calculating
Overflow
Minus Segment H
TMS0101NC Heathkit
IC-2008A
    off

Scanning: Display and keyboard scanning is performed in D11 → D1 direction at a rate of about 584 Hz with the Digits blanked at State S1 and State S13 but no Segment blanking:

State Time = 3 Clocks = 0.012 ms @ CK=250 kHz
Digit Time = 13 States (1 Instruction Cycle) = 0.156 ms @ CK=250 kHz
Scan Time = 11 Digit Times (D1 to D11) = 1.712 ms @ CK=250 kHz

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

Joerg Woerner, March 18, 2023. No reprints without written permission.