TI Little Professor (1978)

Chip labeled 
TMC1993NL
DCW 7845
SINGAPORE

die labeled
1990C-c3C

19 buttons: 0-9, On, Off, Set, Level, Go, +, -, *, /
9 7-segment LEDs ##+##=###

digit 4 is just =

           \./
digit 7 is --- for +, - x, ÷
           /.\
           
   /       \ /   .
 ---  ---       ---
 /         / \   .
 
 pinout
1  digit 5
2  digit 6
3  digit 7
4  digit 8
5  digit 9
6  row 1
7  N/C
8  col 1
9  row 2
10 col 2
11 row 3
12 col 3
13 row 4
14 col 4
15 row 5
16 9v batt -
17 9v batt +
18 seg B
19 seg A
20 seg G
21 seg F
22 seg E
23 seg D
24 seg C
25 digit 4 = (no matter which digit selected)
26 digit 1
27 digit 2
28 digit 3


Key Matrix

OFF         SET   LEVEL
 7     8     9      /
 4     5     6      *
 1     2     3      -
ON     0    GO      +