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Memory Addressing Using the General Assembly Program
The previous discussion has centered on describing the memory addressing features built into
the DATANET-30.
This section will describe the memory addressing features built into the
General Assembly Program.
The General Assembly Program instruction mnemonics and pseudo-operations provide a tech-
nique for program preparation.
This is particularly true· with respect to memory addressing,
since the General Assembly Program does a great deal of the generation and validity checking
of addresses.
The General Assembly Program will interpret an asterisk (*) in the operand field on input data
to mean the address of that instruction.
Location
Instruction
05000
LDA *+ 10
In this example, *
=
05000 and the relative address *+10 will be 05010.
The * serves as a flag to the General Assembly Program and causes the performance of a
special calculation to generate the desired address.
The assembly program is also flagged by the character X in the "X" column. This indicates
that indirect addressing is desired on that instruction. The assembly program generates the
desired address according to the standard rules and then adds a 1-bit in I (12). One other
special requirement must be flagged to the assembly program by the programmer. When it
is desired to use channel table addressing, a symbolic operand must be used and the symbol
must start with the character
$
(dollar sign). The assembly program, upon finding this con-
dition, will assign addressing mode 3 (channel table addressing) by making I (10-11)
=
11.
It
then checks the location of the symbol, verifies that it is less than 8192 and that it is a multiple
of 16 (that the low order
4
bits are all zero), divides the location by 16 and inserts the remaining
9 significant bits in the instruction.
[ID£1J&~~1Jc:J ~@------------
A-18
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