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From: gwyn@BRL.ARPA.UUCP
Newsgroups: comp.sys.apple
Subject: Re:  Changing IIgs Modem port Baud Rate from Basic
Message-ID: <8705280257.aa09776@VGR.BRL.ARPA>
Date: Thu, 28-May-87 02:57:53 EDT
Article-I.D.: VGR.8705280257.aa09776
Posted: Thu May 28 02:57:53 1987
Date-Received: Sat, 30-May-87 01:14:18 EDT
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According to the 8530 SCC info I posted recently, you need to do
something like the following (note: BASIC syntax may be wrong; I
don't use BASIC much).

10000 REM subroutine to alter baud rate of modem port
10001 REM invoke with BR = desired baud rate then GOSUB 10000
10002 REM
10010 REM I assume a 16x clock is being used; could be 1x, 32x, 64x
10011 CX = 16 : REM clock divisor (see above note)
10012 XT = 3.6864 : REM Apple IIGS crystal oscillator frequency, in MHz
10020 TC = INT( (XT / CX) / (2 * BR) * 1000000 - 2 + 0.5 ) : REM time constant
10021 HB = INT( TC / 256 + 0.5 ) : REM high byte of TC
10022 LB = INT( TC - HB * 256 + 0.5 ) : REM low byte of TC
10030 RA = -16328 : REM modem port register adress ($C038)
10031 DA = -16326 : REM modem port data address ($C03A)
10040 POKE RA, 12 : REM prepare to write register 12
10041 POKE RA, LB : REM set low byte of time constant
10045 POKE RA, 13 : REM prepare to write register 13
10046 POKE RA, HB : REM set high byte of time constant
10050 RETURN