Programming:Unlocking a protected basic file

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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.

Emulators

JavaCPC has an "Ignore ,P protection" feature under Configuration ➞ System Settings.

Other Tools

  • Speedcop (part of the Draysoft Doubler package) allows to remove protection from cassette files
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