Creating Proms For Memory Addresses Not In Hardware Configuration; Programming Examples - Texas Instruments 990 Operation Manual

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945255-9701
7 .6.3 CREATING PROMs FOR MEMORY ADDRESSES NOT IN HARDWARE CONFIGU-
RATION. By specifying a load point for the linking loader different from the default, PROMs
may be generated to be used in memory addresses for which memory is not configured in the
current system or cannot be loaded with the linking loader.
An example is to generate a PROM to be used at location FE00
16 .
Since the ROM for the
programmer panel and loader is at location FE00
16 ,
object code cannot be loaded there. The
linking loader provides the capability to load programs with a specified load point and load bias.
This allows the user to load programs at a location in memory different from the location at
which they will execute, FE00
16
in this case.
The load point and load bias specified by the user are used in determining how the code is
relocated and the memory address where the code will actually be loaded. Code assembled with
an absolute origin (AORG) directive is loaded at the absolute address determined by the directive
plus the load point.
MEMLOC
=
ABS ADDR + LDPT
In this example, if the object code to be programmed into PROM is assembled with an absolute
origin of FE00
16
but the user wants to load it at location 200
16 ,
he should enter a load point
of 400
16 ,
The load bias entered is not used since the object code is absolute.
Code assembled with a relocatable origin (RORG) directive is loaded at the relocatable address
determined by the directive plus the load bias plus the load point.
MEMLOC
=
REL ADDR + LDBI + LDPT
In this example, if the object code to be programmed into PROM is assembled with a relocatable
origin of 0, and the user wants it to be executable at location FEOOi6 but wants to load it at
location 200
16 ,
he should enter a load point of 400
16
and a load bias of FE00
16 •
200
16
=
0 + FE00
16
+ 400
16
Note however, that object code loaded with a load point other than the default 0 is not
executable.
7.7 PROGRAMMING EXAMPLES
The following paragraphs present examples of command sequences used to program PROMs with
the PROM programmer and examples of command sequences for using the additional PROM
programmer capabilities. Additional programming examples are presented in Section XI.
7.7.1 EXAMPLE 1. Generate a 256
X
16 memory with PROMs by programming a 256 word
block of memory, located at 7 AO
16,
into four 256 x 4 PROM devices. Refer to figure 7-2.
7-25
Digital Systems Division