ARG Is used for passing parameters to machine code subroutines.
Where D is a Dummy Variable
N is the number to be passed
ARG loads the Z80 E and C registers. They are loaded with the higher and lower byte portions of a 16 bit representation of the ARG argument.
For example if V in the example above was 4100 then;
16x256+4 = 4100
This function is useful when making CP/M system calls to set the C register before a call to location 5. See Machine Code Calls.