Difference between revisions of "Programming:Unlocking a protected basic file"

Revision as of 01:40, 16 April 2010

You can protect a basic program by saving it with

save"filename",p

You can still run" a protected basic file, but can't load" and list it.

That is, after LOADing, the program is automatically deleted when returning to the BASIC prompt. Same applies when stopping a RUNning program via ESC key.

CPC464 Workaround

There is a way to unlock these basic files. This only works on a CPC 464 (real machine or emulator). The used addresses are 464-only (AC01h..AC02h=BASIC RAM, C064h..C090h=BASIC ROM).

Type this:

poke &ac02,&90
poke &ac03,&c0
poke &ac01,&c3

then load" the protected basic file. Done.

Now you can list this program.

CPC664/6128 Workaround

Below installs a resident Fast Ticker handler at BE00h. It resets the "protected file flag" once every 300Hz.

10 FOR i=&BE00 TO &BE0F: READ a$: POKE i,VAL("&"+a$): NEXT
20 CALL &BE00: NEW
30 DATA 21,10,be,11,0b,be,06,81,c3,e0,bc,af,32,2c,ae,c9

In the 664/6128/Plus, that flag is at AE2Ch. For the 464, it would need to be changed to AE45h, or, use the simplier POKE AC0Xh method on CPC464.