The main memory is controlled by the familiar WR and MA wires.

The ALU does the main work of the computer: adding, taking the 2's complement, doing the Boolean logical operations, and other things. Each of these functions is distinguished by a mini-opcode whose binary number is put onto the three wires F0, F1 and F2. Here are the operations that the CSC-1 ALU performs:

  F2  F1  F0
--------------------------------------------------------------------
  0   0   0     identity A     pass through A's value unchanged
  0   0   1     identity TMP   pass through TMP's value unchanged
  0   1   0     A and TMP      bitwise Boolean AND of A and TMP
  0   1   1     A or TMP       bitwise Boolean OR of A and TMP
  1   0   0     not A          bitwise Boolean NOT of A (TMP ignored)
  1   0   1     A + TMP        arithmetic addition of A and TMP
  1   1   0     A - TMP        arithmetic subtraction of A and TMP
  1   1   1     unused