Control Data 3100 Reference Manual page 154

Symbol Assignments
The pseudo instructions, EQU; EQU, C; ENTRY; and EXT define symbols as equal to
other symbols or values, or identify symbols used to communicate with subprograms.
Linkage between symbols in separate subprograms is provided by the monitor system.
These pseudo instructions may appear anywhere between an IDENT and an END
pseudo instruction.
EOU
m -
assigns the result of the expression in the address field to the symbol in the
location field. The result is a 15-bit address.
The following forms are allowed:
symbol EQU symbol
symbol EQU constant (octal or decimal)
symbol EQU expression (address arithmetic)
Example:
OUT EQU JUMP+2
If JUMP is assembled to address 00100, OUT will be assigned the value 00102.
Numerical constants must follow the rules for symbolic instructions. Address arithmetic
is permitted. A location field symbol may be equated to a decimal or octal constant.
EOU,
em-is similar to EQU, except that the result is a 17-bit address.
ENTRY m -
defines location symbols which are referenced in other subprograms. These
symbols, called entry points, must be placed in the address field of an ENTRY pseudo
instruction. Any number oflocations may be declared as entry points in the same ENTRY
instruction. If two or more names appear in the address field, they must be separated
by commas. No spaces (blanks) can appear within a string of symbols. The address field
of the ENTRY pseudo instruction may be extended to column 72 and the location field
must be blank. Only word-location symbols (15-bits) may be used.
Example:
ENTRY SYM1,SYM2,SYM3
SYM1, SYM2, SYM3 can now be referenced by other subprograms.
EXT m -
Symbols used by a subprogram which are defined in another subprogram are
declared as external symbols by placing them in the address field of an EXT pseudo
instruction. Only word-location symbols (15-bit) may be used. For example, to use the
external symbols SYM1, SYM2, SYM3 in subprogram A, the following pseudo instruc-
tion would be written in subprogram A:
EXT SYM1,SYM2,SYM3
These symbols must be declared as ENTRY points in some other subprogram or sub-
programs which are loaded for execution with subprogram A. The address field may be
extended to column 72; symbols are separated by commas. No spaces (blanks) can appear
in a string of symbols. The location field of an EXT must be blank.
Address arithmetic cannot be performed on external symbols.
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