Assembly¶

Assembly code provides a way to specify instructions for the computer to perform in a more human readable from than machine code

Assembly operations and arguments to specify their behaviour can be saved in an assembly file and passed to an assembler to convert them to machine code that the computer can then execute.

These are the operations and other assembly constructs that can be used to create a valid assembly file.

Arithmetic Operations¶

ADD¶

The ADD operation adds the value held in the specified module (or a constant) to the accumulator. The ALU flags generated by this operation are stored.

The possible usages are:

ADD A

ADD B

ADD C

ADD CONST

ADDC¶

The ADDC operation adds the value held in the specified module (or a constant) to the accumulator. If the carry flag is high, an additional 1 is added. The ALU flags generated by this operation are stored.

The possible usages are:

ADDC A

ADDC B

ADDC C

ADDC CONST

SUB¶

The SUB operation subtracts the value held in the specified module (or a constant) from the accumulator. The ALU flags generated by this operation are stored.

The possible usages are:

SUB A

SUB B

SUB C

SUB CONST

SUBB¶

The SUBB operation subtracts the value held in the specified module (or a constant) from the accumulator. If the borrow flag is high an additional 1 is subtracted. The ALU flags generated by this operation are stored.

The possible usages are:

SUBB A

SUBB B

SUBB C

SUBB CONST

LSHIFT¶

The LSHIFT operation moves all the bits in the specified module one place to the left (toward the most significant bit) in place. A zero is added in the rightmost (least significant bit) place. The ALU flags generated by this operation are stored.

The possible usages are:

LSHIFT ACC

LSHIFT A

LSHIFT B

LSHIFT C

LSHIFTC¶

The LSHIFTC operation moves all the bits in the specified module one place to the left (toward the most significant bit) in place. If the carry flag is high, a 1 is added in the rightmost (least significant bit) place. If the flag is low, the rightmost place is left as 0. The ALU flags generated by this operation are stored.

The possible usages are:

LSHIFT ACC

LSHIFT A

LSHIFT B

LSHIFT C

INCR¶

The INCR operation adds one to the given argument (in place). The ALU flags generated by this operation are stored.

The possible usages are:

INCR ACC

INCR A

INCR B

INCR C

DECR¶

The DECR operation subracts one from the given argument (in place). The ALU flags generated by this operation are stored.

The possible usages are:

DECR ACC

DECR A

DECR B

DECR C

Data Operations¶

COPY¶

The COPY operation copies the value from a source module to a destination module. This overwrites the current value of the destination register. It requires a single machine code byte in program memory.

It is used by specifying the source module as the first argument and the destination module as the second.

The possible usages are:

COPY ACC A

COPY ACC B

COPY ACC C

COPY ACC SP

COPY A ACC

COPY A B

COPY A C

COPY A SP

COPY B ACC

COPY B A

COPY B C

COPY B SP

COPY C ACC

COPY C A

COPY C B

COPY C SP

COPY PC ACC

COPY PC A

COPY PC B

COPY PC C

COPY PC SP

COPY SP ACC

COPY SP A

COPY SP B

COPY SP C

LOAD¶

The LOAD operation loads a value from data memory into a module.

It is used by specifying the position in memory as the first argument and the destination module as the second. The position in memory can be a module or a constant and is encased in square parentheses.

The possible usages are:

LOAD [ACC] ACC

LOAD [ACC] A

LOAD [ACC] B

LOAD [ACC] C

LOAD [A] ACC

LOAD [A] A

LOAD [A] B

LOAD [A] C

LOAD [B] ACC

LOAD [B] A

LOAD [B] B

LOAD [B] C

LOAD [C] ACC

LOAD [C] A

LOAD [C] B

LOAD [C] C

LOAD [PC] ACC

LOAD [PC] A

LOAD [PC] B

LOAD [PC] C

LOAD [SP] ACC

LOAD [SP] A

LOAD [SP] B

LOAD [SP] C

LOAD [CONST] ACC

LOAD [CONST] A

LOAD [CONST] B

LOAD [CONST] C

STORE¶

The STORE operation stores a value from a module in memory.

It is used by specifying the module as the first argument and the location in memory as the second. The location in memory can be a module or a constant and is encased in square parentheses.

The possible usages are:

STORE ACC [ACC]

STORE ACC [A]

STORE ACC [B]

STORE ACC [C]

STORE ACC [PC]

STORE ACC [SP]

STORE ACC [CONST]

STORE A [ACC]

STORE A [A]

STORE A [B]

STORE A [C]

STORE A [PC]

STORE A [SP]

STORE A [CONST]

STORE B [ACC]

STORE B [A]

STORE B [B]

STORE B [C]

STORE B [PC]

STORE B [SP]

STORE B [CONST]

STORE C [ACC]

STORE C [A]

STORE C [B]

STORE C [C]

STORE C [PC]

STORE C [SP]

STORE C [CONST]

STORE PC [ACC]

STORE PC [A]

STORE PC [B]

STORE PC [C]

STORE PC [PC]

STORE PC [SP]

STORE PC [CONST]

PROGLOAD¶

The PROGLOAD operation loads a value from program memory into the ACC module.

It is used by specifying the position in program memory as the single argument. The position in memory can be a module or a constant and is encased in square parentheses.

The possible usages are:

PROGLOAD [ACC]

PROGLOAD [A]

PROGLOAD [B]

PROGLOAD [C]

PROGLOAD [PC]

PROGLOAD [SP]

PROGLOAD [CONST]

PROGSTORE¶

The PROGSTORE operation stores the value in the ACC module into program memory.

It is used by specifying the position in program memory as the single argument. The position in memory can be a module or a constant and is encased in square parentheses.

The possible usages are:

PROGSTORE [ACC]

PROGSTORE [A]

PROGSTORE [B]

PROGSTORE [C]

PROGSTORE [PC]

PROGSTORE [SP]

PROGSTORE [CONST]

PUSH¶

The PUSH operation takes a value in a module and add it to the top of the stack.

The stack grows downwards in memory, starting at address 255. The SP module is used to keep track of the top of the stack. The value in SP points at the current top of the stack. SP should be initialised to 0 so that the first push will put the value at address 255. The push first decrements SP, then stores the value in memory at the new value of SP.

The flags generated while decrementing SP are not stored.

The push operation is used by specifying the module to push onto the stack as the first and only argument.

The possible usages are:

PUSH ACC

PUSH A

PUSH B

PUSH C

PUSH PC

POP¶

The POP operation takes the value from the top of the stack and copies it to a module.

The value currently at top of the stack is pointed to by SP. A pop will first copy the value at the top of the stack into a module, then increment SP (the stack grows downwards in memory from address 255).

The flags generated while incrementing SP are not stored.

The pop is used by specifying the module to pop the value off the stack into as the first and only argument.

The possible usages are:

POP ACC

POP A

POP B

POP C

SET¶

The SET operation will set a module in the computer to a given constant value.

It is used by specifying a module as the first argument, then the value to set it to as a constant.

It requires two machine code bytes in program memory. Consider the SET_ZERO operation if the constant is zero.

The possible usages are:

SET ACC CONST

SET A CONST

SET B CONST

SET C CONST

SET SP CONST

SET_ZERO¶

The SET_ZERO operation will set a module in the computer to zero.

The ALU flags generated by this operation are not stored.

It is used by specifying a module as the first and only argument.

The possible usages are:

SET_ZERO ACC

SET_ZERO A

SET_ZERO B

SET_ZERO C

Program Control Operations¶

NOOP¶

The NOOP does nothing - no module transfers occur on the bus for one instruction cycle.

The possible usages are:

NOOP

JUMP¶

The JUMP operation will set the program counter to a value.

The possible usages are:

JUMP ACC

JUMP A

JUMP B

JUMP C

JUMP SP

JUMP CONST

JUMP [ACC]

JUMP [A]

JUMP [B]

JUMP [C]

JUMP [SP]

JUMP [PC]

JUMP [CONST]

JUMP_IF_LT_ACC¶

The JUMP_IF_LT_ACC operation will set the program counter (jump) to the value of a given constant (second argument) if the value of the first argument (module or constant) is less than the accumulator.