95. Auto screen-off
    ~~~~~~~~~~~~~~~
Further to the previous tip, Adrian Botham has written a machine-code routine
which turns the screen display off if no key has been pressed within the
previous minute. As soon as a key is pressed, the screen display magically
reappears with its contents preserved. This helps to lengthen the useful life
of the cathode ray tube by preventing 'phosphor burns'. The code occupies 88
bytes, and I have used the cassette/RS423 input buffer area at &A00. If this
interferes with any of your other software, then you can try putting it
somewhere else.

After running the program, you can load other programs in, switch to Wordwise
etc., and as long as you don't press <Break>, then the 'auto screen-off' will
operate.

Any of you who want to figure out how it works should read chapter 12 of the
Advanced User Guide for the BBC Micro, and also chapter 9.5 and 9.6.

The only spaces in the listing are absolutely essential, and note that the
underline character is used in some variable names, and should not be
confused with the minus sign, which looks very similar in mode 7. (The
underline character is on the same key as the Pound sign.) After typing in
the listing, save the program before attempting to RUN it.

 100 osword=&FFF1:osbyte=&FFF4:evntv=&220
 110 clock_pars=&A00:code%=clock_pars+5
 120 FORpass%=0TO1:P%=code%
 130 [OPTpass%*2
 140 PHP:CMP#2:BEQkey_pressed
 150 CMP#5:BEQminute_up:PLP:RTS
 160 .key_pressed PHA:TXA:PHA:TYA:PHA
 170 LDA#0:STA&FE00:LDA&FE01:BEQturn_screen_on
 180 .set_time LDX#clock_pars MOD256:LDY#clock_pars DIV256
 190 LDA#4:JSRosword:JMPexit
 200 .turn_screen_on LDA#132:JSRosbyte
 210 CPY#&41:BPLfour_seven
 220 .zero_three LDA#127:STA&FE01:JMPset_time
 230 .four_seven LDA#63:STA&FE01:JMPset_time
 240 .minute_up PHA:TXA:PHA:TYA:PHA
 250 LDA#0:STA&FE00:STA&FE01
 260 .exit PLA:TAY:PLA:TAX:PLA:PLP:RTS
 270 ]NEXT
 280 ?evntv=code%MOD256: evntv?1=code%DIV256
 290 !clock_pars=&FFFFE890:clock_pars?4=&FF
 300 *FX14,2
 310 *FX14,5
 320 CALLcode%