2.1.2.5 Address transfer operators

In these instructions, ‘M’ (the address of the instruction after indexing) is used as a number instead of as the address of a memory cell. Consequently, ‘M’ can have any valid word value (i.e., it’s not limited to the 0-3999 range of a memory address).

ENTA

Enter ‘M’ in [rA]. OPCODE = 48, MOD = 2. rA <- M.

ENTX

Enter ‘M’ in [rX]. OPCODE = 55, MOD = 2. rX <- M.

ENTi

Enter ‘M’ in [rIi]. OPCODE = 48 + i, MOD = 2. rIi <- M.

ENNA

Enter ‘-M’ in [rA]. OPCODE = 48, MOD = 3. rA <- -M.

ENNX

Enter ‘-M’ in [rX]. OPCODE = 55, MOD = 3. rX <- -M.

ENNi

Enter ‘-M’ in [rIi]. OPCODE = 48 + i, MOD = 3. rIi <- -M.

INCA

Increase [rA] by ‘M’. OPCODE = 48, MOD = 0. rA <- rA + M.

INCX

Increase [rX] by ‘M’. OPCODE = 55, MOD = 0. rX <- rX + M.

INCi

Increase [rIi] by ‘M’. OPCODE = 48 + i, MOD = 0. rIi <- rIi + M.

DECA

Decrease [rA] by ‘M’. OPCODE = 48, MOD = 1. rA <- rA - M.

DECX

Decrease [rX] by ‘M’. OPCODE = 55, MOD = 1. rX <- rX - M.

DECi

Decrease [rIi] by ‘M’. OPCODE = 48 + i, MaOD = 0. rIi <- rIi - M.

In the above instructions, the subfield ‘ADDRESS’ acts as an immediate (indexed) operand, and allow us to set directly the contents of the MIX registers without an indirection to the memory cells (in a real CPU this would mean that they are faster that the previously discussed instructions, whose operands are fetched from memory). So, if you want to store in ‘rA’ the value -2000 (- 00 00 00 31 16), you can use the binary instruction + 31 16 00 03 48, or, symbolically,

ENNA 2000

Used in conjunction with the store operations (‘STA’, ‘STX’, etc.), these instructions also allow you to set memory cells contents to concrete values.

Note that in these address transfer operators, the ‘MOD’ field is not a subfield specificator, but serves to define (together with ‘OPCODE’) the concrete operation to be performed.