REM ***********************************************************************
REM
REM Parallel Port and Games Port access using STANDARD BASIC only.
REM
REM (C)1996 B.Walker, (G0LCU).
REM
REM This is ready for ~ACE Basic Compiler~, (C) David Benn.
REM
REM ***********************************************************************

REM Open a standard window. This IS needed for ACE Basic Compiler.
  WINDOW 1,"Port Access, (C)1996 B.Walker, G0LCU.",(0,11)-(640,200),6

REM Set up any string variables.
  LET a$="(C)2001 B.Walker, G0LCU."
REM Set up any numerical variables.
  LET n=0
  LET byteval=0

REM ~CIAA~ address for register ~pra~.
  LET pra=12574721
REM ~CIAA~ address for register ~prb~.
  LET prb=12574977
REM ~CIAA~ address for direction of port ~pra~, (1=OUTPUT).
  LET ddra=12575233
REM ~CIAA~ address for direction of port ~prb~, (1=OUTPUT).
  LET ddrb=12575489

REM Store single byte values of these addresses for future use.
  LET valpra=PEEK(pra)
  LET valprb=PEEK(prb)
  LET valddra=PEEK(ddra)
  LET valddrb=PEEK(ddrb)
REM Bit 0 of port ~ddra~ DO NOT CHANGE...
REM Bit 1 of port ~ddra~ switches the ~LED~ ON or OFF, (1=ON).
REM Bits 2 to 5 inclusive of port ~ddra~ DO NOT CHANGE...
REM Bits 6 and 7 of port ~ddra~ alter PIN 6 of the mouse/games ports, (1=OUTPUT).
REM Port ~ddrb~ controls the parallel port, all bits, (1=OUTPUT).
  LET newvalpra=valpra
  IF newvalpra>=128 THEN LET newvalpra=newvalpra-128
  LET newvalddra=valddra
  IF newvalddra>=128 THEN LET newvalddra=newvalddra-128

REM Initial copyright line.
  CLS
  COLOR 1,0
  LOCATE 1,28
  PRINT a$
  GOTO start1:

REM Simple setup screen.
start:
  CLS
start1:
  LOCATE 4,10
  PRINT "Press ~w~ or ~W~ for writing data bytes to the parallel port."
  LOCATE 6,10
  PRINT "Press ~r~ or ~R~ for reading data bytes from the parallel port."
  LOCATE 8,10
  PRINT "Press ~g~ to read from PIN 6 of the games port only."
  LOCATE 10,10
  PRINT "Press ~G~ to write to PIN 6 of the games port only."
  LOCATE 12,10
  PRINT "Press ~l~ to turn the power light UP or ON."
  LOCATE 14,10
  PRINT "Press ~L~ to turn the power light DOWN or OFF."
  LOCATE 16,10
  PRINT "Press ~q~ or ~Q~ to quit."
  
REM This is the main loop.
mainloop:
  LET a$=INKEY$
  IF a$="w" OR a$="W" THEN GOTO parallelwrite:
  IF a$="r" OR a$="R" THEN GOTO parallelread:
  IF a$="G" THEN GOTO gamesportwrite:
  IF a$="g" THEN GOTO gamesportread:
  IF a$="l" THEN GOSUB lightup:
  IF a$="L" THEN GOSUB lightdown:
  IF a$="q" OR a$="Q" THEN GOTO getout:
  GOTO mainloop:

REM Write byte values to the parallel port.
parallelwrite:
  CLS
  LET n=0
REM Set all bits to outputs.
  POKE ddrb,255
loop1:
  POKE prb,n
  LET byteval=PEEK(prb)
  LOCATE 10,19
  PRINT "Decimal value at the parallel port is";byteval;CHR$(8);".   "
  LOCATE 12,26
  PRINT "Press ~SPACE BAR~ to exit."
  LET a$=INKEY$
  IF a$=" " THEN GOTO start:
  LET n=n+1
  IF n>255 THEN LET n=0
  GOTO loop1:

REM Read byte values from the parallel port.
parallelread:
  CLS
REM Set all bits to inputs.
  POKE ddrb,0
loop2:
  LET byteval=PEEK(prb)
  LOCATE 10,19
  PRINT "Decimal value at the parallel port is";byteval;CHR$(8);".   "
  LOCATE 12,26
  PRINT "Press ~SPACE BAR~ to exit."
  LET a$=INKEY$
  IF a$=" " THEN GOTO start:
  GOTO loop2:

REM Write ~1~s and ~0~s to PIN 6 of the games port.
gamesportwrite:
  CLS
REM Force bit 7 of ~pra~ as an output.
  POKE ddra,(newvalddra+128)
REM Set bit 7 of ~pra~ to a value ~1~.
loop3:
  POKE pra,(newvalpra+128)
  LET n=PEEK(pra)
  LOCATE 8,19
  PRINT "Value should be greater than ~127~:-";n;CHR$(8);".   "
REM Set bit 7 of ~pra~ to a value ~0~.
  POKE pra,newvalpra
  LET n=PEEK(pra)
  LOCATE 10,21
  PRINT "Value should be less than ~128~:-";n;CHR$(8);".   "
  LOCATE 12,26
  PRINT "Press ~SPACE BAR~ to exit."
  LET a$=INKEY$
  IF a$=" " THEN GOTO start:
  GOTO loop3:

REM Read the state of PIN 6 of the games port.
gamesportread:
  CLS
  POKE pra,valpra
  POKE ddra,valddra
loop4:
  LET n=PEEK(pra)
  LOCATE 10,9
  PRINT "Less than ~128~ when PIN 6 of the games port pulled LOW:-";n;CHR$(8);".   "
  LOCATE 12,26
  PRINT "Press ~SPACE BAR~ to exit."
  LET a$=INKEY$
  IF a$=" " THEN GOTO start:
  GOTO loop4:

REM Turn the POWER light UP or ON.
lightup:
  POKE ddra,valddra
  POKE pra,252
  RETURN

REM Turn the POWER light DOWN or OFF.
lightdown:
  POKE ddra,valddra
  POKE pra,254
  RETURN

REM Exit routine.
REM Reset all of the ports back to their original state.
getout:
  POKE pra,valpra
  POKE prb,valprb
  POKE ddra,valddra
  POKE ddrb,valddrb
  WINDOW CLOSE 1
  END