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From: jchoi@ics.uci.edu (John Choi)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Need help programming SCC
Message-ID: <27A8D317.5428@ics.uci.edu>
Date: 1 Feb 91 02:31:50 GMT
References: <1991Jan29.205455.26919@sol.UVic.CA>
Reply-To: jchoi@ics.uci.edu (John Choi)
Distribution: na
Organization: UC Irvine Department of ICS
Lines: 63

In article <1991Jan29.205455.26919@sol.UVic.CA> marykuca@sol.uvic.ca (Brent Marykuca) writes:
>
>We are trying to set up a fairly high-resolution timing device based
>on the Time Manager's ability to run a task every millisecond.  Our
>task simply increments a global counter and it seems to give reasonable
>accuracy.  Our difficulty lies in trying to find an input device that
....
>to wire up some sort of device to the serial port which will cause an
>interrupt when one of two buttons is pressed, and then have our interrupt
>handler read the clock for us.
>
>So, what I'm looking for is somebody who has done some low-level serial
>port interrupt handler stuff with the SCC, or any tips at all about how
>to approach this project.  Can anybody help?
>

   I have a similar set-up now using just the normal serial buffer functions
in the Serial Driver Manager.  I have a square pulse generated from a TTL
chip go directly to pin 5 of the modem port with pin 4 as ground.

The program sets up the modem port for regular serial communication at
some arbitrary baud rate.  When the data comes into the port it is stored
in a data buffer.  I clear the data buffer after each 'character' transmission
and store the time away.  My problem is that I can't seem to get Time Manager
to work correctly.  When I set up a loop to increment a global variable
every 5 or 10 counts, each incremented vaule seems to correspond to 1.05 msec
over a range of minutes.  Do you just recalibrate to match real time or
is there a real solution?  I'm using THINK C 4.02 on a Mac II.
    If you don't have this problem, could you send me some of your timing
routines.  Thanks.

Here is the Serial Port stuff - not really complete.

timeSignals()
{
  long     len, config;
  short    inPort;
  char     inBuf[10];
  int      onLine = 1;

  OSErr    anErr;
  EventRecord   anEvent;

  anErr = RAMSDOpen(sPortA);
  inPort = -6;                                  /* Modem port = -6 */
  config = baud9600+data8+stop10+noParity;
  anErr = SerSetBuf(inPort, &inBuf, 10);
  anErr = SerReset(inPort, config);

  while(onLine) {
    anErr = SerGetBuf(inPort, &len);
    if(len){
       anErr = FSRead(inPort, &len, &inBuff);
       timeNow = TickCount();
       if(len > 1) DoErrText("Transfer Buffer Overflow");
    }

    if(GetNextEvent(mDownMask,&anEvent)) onLine = 0;
  }

  RAMSDClose(sPortA);
  return;
}