Chapter
4.
Assembler
Directives
END-OF-TAPE
INDICATION
The EOT directive allows you to specify the physical end
of
paper tape to simplify assembly
of
multiple-tape source
programs.
EOT
Directive
Label
Opcode
Operand
optional:
EOT
When EOT
is
recognized by the assembler, the message 'NEXT TAPE'
is
sent to the console and the assembler pauses.
After the
next
tape
is
loaded, a 'space bar' character received at the console signals continuation
of
the assembly.
Data
in
the operand field
caU5.es
an
error.
LOCATION COUNTER CONTROL AND RELOCATION
All
the directives discussed
in
the remainder
of
this chapter relate directly to program relocation except for the
ASEG
and ORG directives. These directives are described first for the convenience
of
readers who do
not
use the
relocation feature.
Location Counter Control (Non-Re·locatable Mode)
When you elect not to
use
the relocation feature,
an
assembler default generate, an ASEG directive for you. The
ASEG directive
specifies
that
the program
is
to
be
assembled
in
the non-relocatable mode dnd cstablishe, a
location
counter
for the assembly.
The location
counter
performs the same function for the assembler
as
the program counter performs during
execution.
It tells the as',emblel- the next memory location availdble for in'>truction or data assembly.
Initially, the location countel-
i:;
set to Lero. The location counter can
be
altered
by
the ORG (origin) directive.
ORG
Directive
The ORG directive sets the location
counter
to the value specified
by
the operand expre'>sion.
Label
Opcode
Operand
optional:
ORG expression
The location
counter
is
',et to the value
of
the operand expre,sion. Assembly-time evaluation
of
ORG expressions
always yields a modulo 64K address. Thus, the expression always
yield, an address
in
the range 0 through
65,535. Any symbol
in
the expression must
be
previously defined. The next machine instruction or data item
is
assembled
at
the specified address.
4-11
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