National Semiconductor Quiz Kid Racer educational calculator (MM5799) die bonded to PCB die marked MM4799 DUZ 20 buttons: 0-9, +, -, x, /, Slow, Fast, Amateur, Pro, Complex, Tables 8 7-segment LEDs, 3rd from right is just =, 6th can display +-x/ 1 green "right" LED MM5799 Pinout 1 K1 keypad col 1 (left) 2 K2 keypad col 2 3 K3 keypad col 3 4 K4 keypad col 4 5 INB N/C 6 SYNC N/C 7 OSC N/C 8 F3 N/C (competition cable data in) 9 F2 N/C (competition cable detect) 10 F1 N/C 11 PO N/C 12 Sp LED decimal point (not used) (competition cable data out) 13 Sg LED segment G 14 Sf LED segment F 15 Vss batt + 16 Se LED segment E 17 Sd LED segment D 18 Sc LED segment C 19 Sb LED segment B 20 Sa LED segment A 21 Vdd Batt - 22 BLK N/C 23 SO N/C 24 SI N/C (competition cable master/slave) 25 D04 DS8874 data 26 D03 N/C 27 D02 N/C 28 D01 DS8874 clock The program outputs 1111-0110 on D port which clocks a 1 bit through the DS8874 shift register to strobe the digits and keypad rows button matrix K1 K2 K3 K4 out 4 AMATEUR PRO COMPLEX TABLES out 5 7 8 9 / out 6 4 5 6 x out 7 1 2 3 - out 8 SLOW FAST 0 + Patent shows test buttons on output 3. LEDs Green "Right" LED connected to DS8874 output 9 out 8 out 7 out 6 out 5 out 4 out 3 out 2 out 1 - - - - - - | | | | \|/ | | | | - | | | | - - - - - - - | | | | /|\ | | | | - | | | | - - - - - - A A A A A A F B F B FAB F B F B A F B F B G G E G G G G E C E C CDG E C E C G E C E C D D D D D D Output PLA: (no 8) 7F - blank 40 - 0 79 - 1 and / 24 - 2 30 - 3 19 - 4 and X 12 - 5 02 - 6 78 - 7 10 - 9 06 - E 23 - o 06 - E 66 - + 6F - - 01 02 08 04 The unit I have does not have the competition cable connector, but I think it is wired as follows: Cable Detect is F2 Master/Slave is SI Data in is F3 Data out is segment DP F1 is also used as output in the code