The Microcontroller Idea Book - Jan Axelson's Lakeview Research

Chapter 14
For experienced assembly-language programmers, another reason for placing BASIC-52 in
external memory is so that you can modify the source file for BASIC-52. You then can
reassemble your modified source file and use the new version in your projects. In this way,
you can add functions or make other changes to BASIC-52 itself. To do this, you must have
a copy of BASIC-52’s source code, which has been available on Intel’s and Philips’ BBS’s,
plus Intel’s ASM51 or a compatible 8051-family assembler.
Iota Systems is one vendor that has customized BASIC-52 in this way, with an expanded
BASIC-52 PLUS that runs from external EPROM on Iota’s 8052-BASIC boards. BASIC-52
PLUS includes commands for uploading and downloading Intel Hex files, as well as other
enhancements and bug fixes.
Copying BASIC-52
To copy BASIC-52 from ROM to NVRAM, you can use the same circuits shown in Figures
3-1 and 4-3. Use a DS1225 8K NV RAM at U8. Listing 14-1 is a program that copies the
8052-BASIC’s ROM from 0 to 1FFFh in internal code memory to U8 at 8000-9FFFh in
external data or code/data memory. Boot up your system, enter or upload Listing 14-1 and
run it. Then power down and remove the NV RAM at U8, which now contains a copy of
BASIC-52.
If you prefer, you can use a 28(C)64 8K EEPROM instead of NV RAM at U8. Because the
write-cycle time of EEPROMs is often 2 to 10 milliseconds, you may have to slow Listing
Listing 14-1. Copies the BASIC-52 interpreter program from ROM to
NVRAM.
10 PRINT “copying BASIC-52 from ROM to RAM at 8000h...”
20 FOR I=0 TO 1FFFH
30 XBY(I+8000H)=CBY(I)
40 NEXT I
50 PRINT “verifying...”
60 X=0
70 FOR I=0 TO 1FFFH
80 IF XBY(I+8000H)CBY(I) THEN GOSUB 120
90 NEXT I
100 IF X=0 THEN PRINT “Copy successful”
110 END
120 PH0. “Error at location ”,I
130 X=1
140 RETURN
240 The Microcontroller Idea Book