Texas Instruments TI-55

chip top marked TMC1503NL DD 8035 30329 SINGAPORE
die labeled T1500D 1503D (c) 11-76

12 7-segment LEDs (leftmost only has segments DP and G, rightmost doesn't have DP)
40 pushbuttons

                        keypad layout
-------------------------------------------------------
          Pin 16  Pin 17   Pin 18  Pin 19   Pin 20
Pin 26     2nd     sin      cos     tan      CLR
Pin 27     INV      %       lnx     e^x    x root y
Pin 24    x<->y    x^2     sqrt     1/x      y^x
Pin 28     S+      EE        (       )        /
Pin 25     STO      7        8       9        *
Pin 23     RCL      4        5       6        -
Pin 22     SUM      1        2       3        +
Pin  2     CE       0        .      +/-       =

Pin 1  - power switch to battery pack black
Pin 2  - segment DP, keypad row 1 (bottom), digit 1 (rightmost)
Pin 3  - digit 2
Pin 4  - digit 3
Pin 5  - digit 4 
Pin 6  - digit 5
Pin 7  - digit 6
Pin 8  - digit 7
Pin 9  - digit 8
Pin 10 - battery pack red
Pin 11 - digit 9
Pin 12 - digit 10
Pin 13 - digit 11
Pin 14 - 0.01uF cap to pin 1
Pin 15 - 220K resistor to pin 10
Pin 16 - keypad column 1 (leftmost)
Pin 17 - keypad column 2
Pin 18 - keypad column 3
Pin 19 - keypad column 4
Pin 20 - keypad column 5 (rightmost)
Pin 21 - N/C
Pin 22 - segment D, keypad row 2, digit 12 (leftmost)
Pin 23 - segment A, keypad row 3
Pin 24 - segment B, keypad row 6
Pin 25 - segment C, keypad row 5
Pin 26 - segment E, keypad row 8 (top)
Pin 27 - segment F, keypad row 7
Pin 28 - segment G, keypad row 5