The Modcomp II was a 16-bit minicomputer circa 1970. As well as in FORTRAN IV, the Modcomp family could be programmed in assembly language, with syntax like this excerpt from Kermit for Modcomp:
HZS,POSIT * STM,2 $+5 NO - ATTACHED FILE LDI,2 POSUFT ASSIGN TO THE ATTACHED FILE REX,#A * DFC $$ * POSIT LDI,2 POSUFT POSITION THE FILE
I am unsure of the meaning of the symbols
$$ in this excerpt. I think that
$ most likely means "address of the instruction being assembled"; I will present my reasoning below. However, other than that
$$ is 16-bits (one word) long, I have no idea what it means.
Q: What are the meanings of the symbols
$$ in Modcomp assembly language, especially as used for the Modcomp II minicomputer?
Why I think that
$ probably means "Address of current instruction":
STM,2 $+5 NO - ATTACHED FILE
STM instruction stores a register into a memory location that will be an argument to a system call.
LDI,2 POSUFT ASSIGN TO THE ATTACHED FILE
LDI instruction loads a constant into a register.
This one word instruction performs a system call.
DFC $$ *
This "define constant(s)" assembler directive reserves (and possibly initializes--I don't know) one word that I presume is used as an argument to the system call.
In order for the
STM instruction to store a register into the word reserved by the DFC,
$ would have to mean "the address of the beginning of the
STM instruction, so that
$+5 would refer to the address of the DFC itself.