Wiz-A-Tron chip top marked TMC0907NL ZA0379 BSP 7723 chip bottom marked DP0907BS SINGAPORE die labeled 0970F-07B 9 7-segment LEDs (1,2,4,5,7,8,9 normal, 3 has special segments to create +, -, X, /, 6 only has segments A and G for =) 16 pushbuttons - 0-9, Clear, =, +, -, X, / keypad layout -------------------------------------- Pin 5 Pin 6 Pin 7 Pin 8 Pin 13 7 8 9 / Pin 15 4 5 6 X Pin 16 1 2 3 - Pin 17 CLR 0 = + Pin 1 - Digit 3 Pin 2 - Digit 2 Pin 3 - Digit 1 Pin 4 - 9V battery negative Pin 5 - keypad column 0 Pin 6 - keypad column 1 Pin 7 - keypad column 2 Pin 8 - keypad column 3 Pin 9 - N/C Pin 10 - N/C Pin 11 - Segment G Pin 12 - Segment F Pin 13 - Segment E Pin 14 - N/C Pin 15 - Segment D Pin 16 - Segment C Pin 17 - Segment B Pin 18 - Segment A Pin 19 - N/C Pin 20 - 9v battery positive (via on/off switch) Pin 21 - Digit 9 Pin 22 - N/C Pin 23 - N/C Pin 24 - Digit 8 Pin 25 - Digit 7 Pin 26 - Digit 6 Pin 27 - Digit 5 Pin 28 - Digit 4 Output O PLA 01111110 0 00110000 1 01101101 2 01111001 3 00110011 4 01011011 5 01011111 6 01110000 7 01111111 8 01111011 9 00100110 + 00000010 - 00110101 X 01001010 / 00000101 r 00000000