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From: neil@cs.hw.ac.uk (Neil Forsyth)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: Forcing the scan rate to 50Hz  [Sure wish they wouldn't!]
Message-ID: <2613@odin.cs.hw.ac.uk>
Date: 25 Mar 91 08:55:18 GMT
References: <95276@tut.cis.ohio-state.edu> <A0b2gh2g@mwowm.mantis.co.uk> <1991Mar20.052658.9162@wam.umd.edu>
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Reply-To: neil@cs.hw.ac.uk (Neil Forsyth)
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Organization: Computer Science, Heriot-Watt U., Scotland
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In article <1991Mar20.052658.9162@wam.umd.edu> dmb@wam.umd.edu
(David M. Baggett) writes:
]The only real reason game writers alter the scan rate is so the game 
]play timing won't change.  Games run 16.3% faster on U.S. ST's because
]the scan rate is 60Hz here.  This means Joust, e.g., is more difficult
]in the U.S.  than it is in the UK, something I always make clear when
]comparing high scores with my British competitors.  :-)

Don't listen to him folks! He's just a sore loser! :-) x 10E6

]An example of a problem caused by the scan rate difference is the
]treasure room in Guantlet II.  U.S. players will notice that the timer
]only counts down to about 4 or so, then the level ends.  This is
]because the countdown code stupidly relies on the scan rate being only
]50 frames per second (it counts a second by waiting for 50 vblanks to
]elapse).  On U.S. machines 50 vblanks occur in 5/6ths of a second, so
]the timer counts down too quickly, and you only get 16.6 seconds in
]the treasure room instead of the normal 20.  (Or is it 25?)

Leaderboard conversely assumes a 60Hz frame rate. I'm not sure how this
affects the game but it really screws up the demo when in 50Hz. The guy
plays bad and doesn't sink the put.

Proper timing should be done using Timer A in the MFP or by latching on to
the system timer (Timer C) which is 200Hz everywhere (a configuration I
believe that should not be changed).

]Dave Baggett
]dmb%wam.umd.edu@uunet.uu.net

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!                                                                            !
! Neil Forsyth                      JANET:  neil@uk.ac.hw.cs                 !
! Dept. of Computer Science         ARPA:   neil@cs.hw.ac.uk                 !
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! Edinburgh, Scotland, UK           "That was never treasure chests!"        !
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