Echelon Neuron - Manual (Page 135)

SUB (Subtract)
The SUB instruction subtracts two numbers. The SUB instruction uses the
direct addressing mode, in two forms, subtract NEXT from TOS, and subtract
TOS from NEXT:
• The SUB NEXT,TOS instruction retrieves both TOS and NEXT from the
data stack and subtracts NEXT from TOS. TOS and NEXT are
consumed, and the result is placed in TOS. The operation modifies the
Carry flag as result of the unsigned subtraction: if the value of TOS
exceeds the value of NEXT (indicating that the result would be negative),
the SUB instruction sets the Carry flag; otherwise the instruction clears
the Carry flag.
• The SUB TOS,NEXT instruction retrieves both TOS and NEXT from the
data stack and subtracts TOS from NEXT. TOS and NEXT are
consumed, and the result is placed in TOS. The operation modifies the
Carry flag as result of the unsigned subtraction: if the value of NEXT
exceeds the value of TOS (indicating that the result would be negative),
the SUB instruction sets the Carry flag; otherwise the instruction clears
the Carry flag.
The SUB instruction applies to Series 3100, 5000, and 6000 devices.
Syntax:
The SUB instruction requires two operands:
SUB NEXT,TOS
SUB TOS,NEXT
Table 56 describes the attributes of the SUB instruction.
Table 56. SUB Instruction
Instruction Hexadecimal
Opcode
Instruction
Size (Bytes)
CPU Cycles
Required
Affect on
Carry Flag
SUB NEXT,TOS 57 1 4 Modified
SUB TOS,NEXT 55 1 4 Modified
Example:
The following example performs the operation 3-2 and the operation 2-3.
pushs #3 ; (3, -, -)
pushs #2 ; (2, 3, -)
sub next,tos ; (1, -, -)
pushs #3 ; (3, 1, -)
pushs #2 ; (2, 3, 1)
sub tos,next
; (255, 1, -)
Neuron Assembly Language Reference 125