The Microcontroller Idea Book - Jan Axelson's Lakeview Research

Chapter 13
Most 8051-family cross-assemblers create files in Intel Hex format, which is convenient for
EPROM programming and uploading to RAM. During the assembly process, if the assembler
encounters a program line that is incomplete or not understandable, it will display an
error message describing the problem. The assembler will also create a listing file that shows
each line of your source file alongside the addresses and machine codes of the object file
and any error messages generated.
Memory for Program Storage
On your BASIC-52 system, you’ll need room in external memory for storing your assembly-language
routines. Remember that the 8052 has separate control signals for accessing
code and data memory. For uploading into RAM and testing, you must use combined
code/data memory, since you need data memory’s WR signal to write the routine into
memory, and code memory’s PSEN to enable the 8052 to execute the routine.
You can upload routines into any unused combined code/data memory from 2000h to FFFFh.
Code memory from 0 to 1FFFh is not available, because the 8052-BASIC chip uses these
locations for the BASIC-52 interpreter. If you have a 32K RAM addressed at 0 in combined
code/data memory, you can use the area above 1FFFh for storing and testing assembly-language
routines. For combined data/code memory in Figure 3-1’s circuit, move the connection
at pin 22 of U7 from pin 17 of U2 (READ) to pin 3 of U3A (RDANY). With this setup,
however, if you upload your programs into ordinary RAM, you’ll lose them when you power
down.
For more permanent storage, there are several options. You can use a 32K NV RAM, such
as Dallas Semiconductor’s DS1235, or a Dallas 1213C SmartSocket and 62256 SRAM, in
place of ordinary RAM at 0. Although you don’t need battery backup for data memory from
0 to 1FFFh, it does no harm. Again, you must connect RDANY, not READ, to pin 22 of the
NVRAM.
To prevent overwriting your assembly-language routines in RAM when you reboot, set
MTOP to 1FFFh, or another value that is lower than the beginning of your routines, and
execute BASIC-52’s PROG3 command, as described in Chapter 3. (You must have NV
memory at 8000h to save MTOP.)
If you use a 32K NV RAM from 0 to 7FFFh, you should be aware that BASIC-52 reserves
two areas of code memory for optional additions and enhancements. One area, from 2001h
to 2091h, stores information that tells BASIC-52 about custom reset routines, keywords and
other language extensions. Another area, from from 4003h to 41FFh, stores information
about user-defined assembly-language interrupt routines.
If you won’t be using these abilities, you can use these areas of memory for other purposes.
However, if at all possible, it’s a good idea to avoid writing to locations 2001h, 2002h, and
220 The Microcontroller Idea Book