Sinclair Cambridge Programmable calculator (MM5799)

chip marked
/751
MM5799NBP/N

die marked MM4799 NBP

19 buttons: 0-9, +, -, x, /, =, EE ^v C/CE, RUN
9 7-segment LEDs
DS8874 LED driver

MM5799 Pinout
1  K1     keypad
2  K2     keypad
3  K3     keypad
4  K4     keypad
5  INB    N/C
6  SYNC   N/C 
7  OSC    N/C
8  F3     N/C
9  F2     K3
10 F1     N/C
11 PO     N/C
12 Sp     LED decimal point and DS8874 low batt
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 - via switch
22 BLK    N/C
23 SO     N/C
24 SI     N/C
25 D04    DS8874 data
26 D03    N/C
27 D02    N/C
28 D01    DS8874 clock



button matrix
           K1             K2              K3             K4
out 3      0              6               =              ^v
out 4      1              7               -             C/CE
out 5      2              8               /              RUN
out 6      3              9               +              --
out 7      4              EE              x              --
out 8      5              --              --             --