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From: reeder@reed.UUCP (Doug Reeder)
Newsgroups: comp.sys.apple2
Subject: Re: Display Softswitches
Message-ID: <15593@reed.UUCP>
Date: 23 Oct 90 04:01:16 GMT
References: <2142@unsvax.NEVADA.EDU>
Reply-To: reeder@reed.UUCP (Doug Reeder)
Organization: Tether Propulsion Division, Institute of Knowledge, Jinx
Lines: 19

In article <2142@unsvax.NEVADA.EDU> alfter@uns-helios.uucp (SCOTT ALFTER) writes:
_Switch    Description                           Address
_--------- ------------------------------------- -------
_VBL       read vertical blanking                C019
_
_Also, VBL doesn't indicate the setting of a switch, but indicates when the
_video circuitry isn't tracing the picture.  For smoother graphics, only change
_the screen contents when the high bit of VBL is clear.

    Note, however, that this won't work on a IIc, because Vertical Blanking
is available only as an interrupt.  (And what fun it is to have a source of
regular interrupts!)


-- 
Doug Reeder                                   USENET: ...!tektronix!reed!reeder
from ARPA: tektronix!reed!reeder@berkeley.EDU BITNET: reeder@reed.BITNET
7th: Each swallow works hard to be perfect pilot-provider-builder-trainer-
teacher-lover-mate,no half-true hate!   - Dr.Brommer's 18-in-1 Pure Castile Soap