Download Print this page

Program Linking Codes (Entry And Extrh) - RCA Spectra 70 Training Manual

System
Hide thumbs

Advertisement

Table of Contents
ADDRESS (EXPRESSION) CONSTANT
An address may be stored as a two-byte constant.
There must be a separate statement line for each
constant of this type. The constant is enclosed in
parenthesis and preceded by an A as in the follow-
ing example s.
1.
2.
3.
Explanation
OPERATION
OPERAND
DC
A(*-6)
DC
ACSTRT)
DC
A(256)
1.
stores the current value of the Location Counter
- 6 as a constant (RELOCATABLE).
2.
Stores the value of STRT as a constant (RE-
LOCATABLE).
3.
Stores the binary equivalent of 256 as a con-
stant (NOT RELOCATABLE).
DEFINING REPETITIVE CONSTANTS
Constants in character and hexadecimal form may be
defined in repetitive fashion.
gC'cv'
gX'cv'
In the format above, g represents the actual number
of constants to be generated, and 'cv' represents
the constant value.
The statements,
NAME
CONI
CON2
OPERATION
OPERAND
DC
DC
3C'ABC'
2X'3F4'
generate ABCABCABC and 03F403F4.
The g factor may not be properly incorporated in an
address constant statement.
The implied length of CONI and CON2, in the above
example, is three and two.
19
DEFINING EXPLICIT CONSTANT LENGTHS
The define constant format may be expanded to in-
clude specific references to length.
gCLn'cv'
gXLn'cv'
ALn'cv'
L may not exceed 256 10
n
=
number of bytes
n may not exceed (16)10
The explicit length takes precedence if it does not
correspond to the physical length of the 'cv' value.
NAME
OPERATION
OPERAND
GENERATED
DC
DC
DC
2C L3
t
ABC
t
ABCABC
2XL5 '3F6'
00000003F600000003F6
2CL2
t
lAB'
lAlA
In the third example above, the B, rightmost char-
acter of the constant lAB, was truncated because a
length of two was specified. In like manner, the
constant defined on the second line was padded-out
to a length of fi ve .
If an explicit length is not included when defining an
ExpressionConstant, a lengthof 4 bytes is assumed,
and the generated constant is aligned on an even word
boundary.
When a length other than four (4) is specified, the
constant is not aligned and is not relocatable. If the
value of the expression exceeds the assigned num-
ber of bytes, the high-order bits of the value are
truncated.
Absolute expressions may have negative values which
are generated in 2's complement form.
Example:
NAME
OPERATION
OPERAND
CONI
DC
All (-2)
CON2
DC
ALI (-5)
PROGRAM LINKING CODES
Generated
Binary Constant
11111110
11111011
The two codes, ENTRY and EXTRN, provide com-
munication between two programs that have been
assembled independently. The ENTRY code speci-
fies the location(s) addressed by another program.
The EXTRN code defines a symbol in another pro-
gram.
ENTRY CODE
A separate ENTRY verb must appear for each entry
point in the program (see START code for exception).
ENTRY appears in the OPERATION field and a sym-
bol must be used in the OPERAND field. The NAME
field is not used on this line.

Advertisement

Table of Contents
loading

  Also See for RCA Spectra 70

  Related Manuals for RCA Spectra 70

  Related Content for RCA Spectra 70

This manual is also suitable for:

Spectra 70/25