SBYTES device_file,start,length or
SBYTES device_file,start[,length[,data[,extra[,type]]] (Minerva v1.80+) or
SBYTES [device_]file,start,length(Toolkit II) or
SBYTES #channel,start,length(SMS only)
|Location||QL ROM, Toolkit II|
It can sometimes be useful to save part of the QL’s memory to a file so that it can be loaded back into the computer at a later date. The area of memory saved may for example, contain a program, some machine code or some data.
The command SBYTES allows you to save length number of bytes from the QL’s memory, starting from the specified start address. The area of memory is saved to the specified file which must include the name of the device to be used, unless Toolkit II is present, in which case the default data device is supported. The Toolkit II variant will also provide you with the option of overwriting the file if it already exists.
To save the currently displayed screen on a standard QL, use the command:
Or under SMS, you can save any size screen using:
SBYTES flp1_Example_scr, SCR_BASE, SCR_LLEN * SCR_YLIM
The start of a program which was protected by a password could be written along the lines of this:
100 a=ALCHP(100) 110 IF FTEST(flp1_pass)=0 120 LBYTES flp1_pass,a 130 END IF 140 pass$='' 150 PAPER#0,0:CLS#0:INK#0,7 160 PRINT #0,'Enter Password :'; 170 FOR letter=1 TO 4 180 pass$=pass$&INKEY$(-1) 190 PRINT#0,'*'; 200 END FOR letter 210 PRINT #0 220 IF PEEK(a)=0 230 offset=RND(1 TO 50) 240 POKE a,offset 250 FOR i=1 TO 4 260 POKE a+i,CODE(pass$(i))+i+offset 270 END FOR i 280 FOR i=5 TO 100:POKE a+i,RND(100) 290 SBYTES flp1_pass,a,100 300 ELSE 310 offset=PEEK(a) 320 FOR i=1 TO 4 330 IF CODE(pass$(i))<>PEEK(a+i)-i-offset 340 PRINT 'Access Denied':RECHP a:STOP 350 END IF 360 END FOR i 370 END IF 380 PRINT 'Access Granted' 390 RECHP a
On Minerva ROMs (pre v1.80), if SBYTES was aborted for some reason whilst writing to a file, the file would be deleted. On later versions of Minerva and all other QL ROMs, the incomplete file is kept and on Toolkit II, the error ‘Medium Full’ is reported.
On Minerva ROMs (pre v1.83) SBYTES set the wrong file type.
The Minerva variant is unfortunately overwritten by the Toolkit II version of this command.
On Minerva v1.80 (or later) the commands SBYTES and SEXEC have practically become interchangeable, as both support exactly the same parameters. All of the parameters except for the start address and device_file where the data is to be stored, are optional and will default to 0 if not specified.
These additional parameters have the following uses:
- Extra This sets the value which is normally returned with FXTRA (which would normally have to be altered with SetHEAD).
- Type This allows you to set two file attributes:
- the file type - this is normally 0 for data, or 1 for executable programs. This is calculated by PRINT type && 255.
- the file access key - it is generally used by Toolkits such as QL-System to store various file attributes (such as whether a file is read-only). This is calculated by PRINT type DIV 256.
The only problem with using this extended version of SBYTES instead of using SEXEC is that you must remember to specify a file type of 1 if the file is later to be EXECuted (as this defaults to 0 in the case of SBYTES!).
For example, both of these are the same:
SBYTES ram1_test_exe, code_start, 20000, 500, 0, 1 SEXEC ram1_test_exe, code_start, 20000, 500
The fourth variant of the command allows you to save the bytes to an existing channel which is already OPEN to a file, thus allowing you to work more efficiently. You can use the following to error trap the saving routine:
100 REPeat loop 110 ch=FOP_NEW (ram1_test_bin) 120 IF ch<0 130 REPORT ch 140 PRINT "Press <y> to retry, <n> to stop" 150 REPeat kLoop 160 key$=INKEY$(-1) 170 IF key$ INSTR 'yn':EXIT kLoop 180 END REPeat kLoop 190 IF key$=='y':NEXT loop 200 STOP 210 END IF 220 SBYTES #ch,131072,32768 230 EXIT loop 240 END REPeat loop 250 CLOSE #ch