ZX Computings - OpenLibra

the new address (in decimal)
followed by NEWLINE. I spent
many happy minutes stepping
through Clive's ROM after
entering "N" NEWLINE, 0
NEWLINE, followed by a succession
of NEWLINEs. If you
have the patience you could list
and disassemble the ROM
(please send me a copy). Any
area of RAM or ROM can be examined
in this way. If you have
the program operating correctly
the first ten bytes of ROM
should read:
Address
0
1
3
4
5
6
7
8
9
10
Decimal Content
211
253
255
127
195
203
3
42
22
64
The next step was to try some
machine code that actually did
something, so I decided to produce
a short tone for my add on
sound box. (Use any amplifier
of 2 mV sensitivity plugged into
mic. socket of your computer.)
Producing a Bleep
So GOTO 10 followed by
NEWLINE produced 16514
38. The 38 was simply the first
letter A of my REM statement.
The following code was then
written in:
Address Decimal Byte
16514 14
16515 255
16516 6
16517 112
16518 211
16519 255
16520 16
16521 254
16522 6
16523 112
16524 237
16525 64
16526 16
16527 254
16528 13
16529 32
16530 241
16531 201
With some trepidation, I set the
address to 16514 and pressed
"R" NEWLINE. My sound box
bleeped happily and I heaved a
sigh of relief. (Use appendix A
of the Sinclair Manual, if you
want to convert the code to hex
and unravel the bleep program.)
It didn't Crash
I accidentally displayed the
REM statement with the code in
it and to my amazement it
didn't crash. Where it encountered
a naughty code,
clever old Clive's ROM simply
told it to display a question
mark.
Machine code
In Summary
This will definitely be my
favourite method of entering
machine code since:
1. It's immobile and absolute
addressing can be used.
2. It's crash proof even if REM
is displayed.
3. It can be saved.
Using the experimental program
also allows you to step
through and examine the ROM
and incidentally, run parts of
the ROM, to find out start addresses
of useful subroutines.
Use the program and have a
dabble with machine code
yourself.
ZX COMPUTING SUMMER 1982 116