Mostek MK50312 - 8-digit calculator, 9 function (+, -, x, /, %, $, SQRT, X^2, 1/X), seven memory functions
              _____ _____
             |     U     |              Keyboard Matrix: 
 (+9V) Vss --| 1      28 |-- f               KN    K0    KS   Note: KS = KN && K0 
         g --| 2      27 |-- b          D0         CM
         d --| 3      26 |-- a          D1   1     %
         e --| 4      25 |-- c          D2   2     sum   =
        dp --| 5      24 |-- ISET       D3   3     M-=   M-
        D0 --| 6      23 |-- Vdd (Gnd)  D4   4     SQRT  X^2
       N/C --| 7      22 |-- KN         D5   5     1/X   .
       N/C --| 8      21 |-- D1         D6   6     $     /
        K0 --| 9      20 |-- D2         D7   7     M+=   M+
       N/C --| 10     19 |-- D3         D8   8     XM    x
       D11 --| 11     18 |-- D4         D9   9     MS    -
       D10 --| 12     17 |-- D5        D10   0     MR    +
        D9 --| 13     16 |-- D6        D11         C/CE
        D8 --| 14     15 |-- D7
             |___________|             Note: D0, D10, D11 are for keyboard matrix only

Taken from data for MK50311 chip which has the same pinout, I have assumed same functions, might be wrong … The TRQ F-85 calculator, that uses this chip, has a switch with two positions 'N' and '∑', I'm not sure how this is connected. I think it may switch a line between the 'KS' column and the 'KO' column, so if that line is connected to the “=” key it would switch its function from “=” to “sum” going by the table above. (The wiring of the TRQ F-85 board confirms the keyboard digit→row associations) ¹⁾

• Corvus 615
• Corvus 615
• Corvus 804
• F-84, Electrónica Querol (TRQ) F84. ²⁾
• F-85, Electrónica Querol (TRQ) F85. ³⁾