-----Oorspronkelijk bericht-----
Van: Manuel Bilderbeek <[EMAIL PROTECTED]>
Nieuwsgroepen: comp.sys.msx
CC: [EMAIL PROTECTED] <[EMAIL PROTECTED]>; [EMAIL PROTECTED] <[EMAIL PROTECTED]>;
[EMAIL PROTECTED] <[EMAIL PROTECTED]>
Datum: donderdag 9 juli 1998 19:26
Onderwerp: IMPORTANT FOR CODERS: please read this!
:Hi MSX coders!
:
:The Sony 900 series is a great, but a bit strange machine! This is
:probably the only MSX machine that doesn't like wrong bits in PSG
:register 7... I base this statement on the fact that some programs
:don't work correctly on this machine. E.g.: The Shrines of Enigma
:(joystick control doesn't work), The Futuredisk (Mouse/Joystick doesn't
:work after a sound-effect, already contacted the author), the old
:version of Bomberman (Antal, the author helped me to find the problem,
:and found it! Thanks!), ... and maybe more.
:
:So, what is the problem? It's the direction-bits of PSG register 7! I
:quote from The MSX RED book:
:
:PSG REGISTER 7:
: This register enables or disables the Tone Generator and
:Noise Generator for each of the three channels: 0=Enable
:1=Disable. It also controls the direction of interface ports A
:and B, to which the joysticks and cassette are attached:
:0=Input, 1=Output. Register 7 must always contain 10xxxxxx or
:possible damage could result to the PSG, there are active
:devices connected to its I/O pins. The BASIC "SOUND" statement
:will force these bits to the correct value for Register 7 but
:there is no protection at the machine code level.
:--------------
:
:So, be careful that the left 2 bits are always "10"!!! This was the
:mistake Antal made in Bomberman. And probably it's the mistake Jan van
:Valburg made in The Shrines of Enigma! And the same goes for Jeroen
:Smael of The Futuredisk.
:
:Appearantly, this only gives trouble in case of the Sony 900 series...
:So, I beg you coders: take care when writing to PSG register 7!!
:
:With thanks to Antal van Kalleveen of Paragon Productions...
:
:Antal also told me that this bug is in a routine published in the Dutch
:Magazine MCCM 71, in "Noorder Baken". So watch out, if you use this
:routine!
Ehmm... elk overzicht van de PSG-registers vermeldt dit. Alleen eh... ik
dacht dat het 00 was... even opzoeken...
Ik heb ontdekt dat toch best wel veel 'oude' boeken het er niet over hebben.
Echter, in MiLC staat her er vast wel overal bij, het staat me in ieder
geval bij dat ik op een gegeven moment even de PSG ging uitzoeken en dat ik
toen werd doodgegooid met waarschuwingen. Ik denk overigens dat het je MSX
echt niet kapot kan maken hoor, zou wel stom zijn, twee van zulke domme
bitjes die je makkelijk verkeerd kan zetten...
Anyway, mijn 'superboek' zegt dat bit 6 Poort A in/uit en bit 7 poort B
in/uit is.
1=uitvoer staat er ook bij. Lijkt me dus dan dat ze allebij op 0 moeten.
Trouwens, je hoeft hier echt niet aan te zitten wanneer je output wilt doen
met de joystick (output/trigger1/trigger2-pinnen).
~Grauw
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