modem DTR signal on Mac II different than Mac IIci????????

modem DTR signal on Mac II different than Mac IIci????????

Post by Phil Hu » Thu, 18 Mar 1993 19:43:45


I have a Telebit Worldblazer modem here at work...It was connected to a
Mac IIci.  When it was connected this way, CTS and MR lights were always on
and the DTR light would come on when my comm s/w made a call.  This worked

Here's the problem....
I moved the entire setup...modem/cable and software verbatim to an old Mac
II we have and now the modem lights CTS, MR and DTR are always on!  Without
and changes to software or hardware (except computer change)!!!!!

This makes it hard for the comm software to reset the modem, since it cannot
drop DTR....

Is DTR handled differently on a II vs a IIci?


Phil Hunt                          "Wherever you go, there you are!"
Howtek, Inc.                              


1. Changing DTR on a Mac II serial port

I want to use the DTR line on the modem port of a Mac II to send
a timed pulse to some lab equipment.  I am totally unfamiliar
with low-level programming on the Mac so I need help bad! My assumption is
that I can write to the control register on the Z8530 by writing a control
byte to address sccWBase+aCtl.  Is that correct?  Next question: What
is the numeric value of sccWBase and aCtl on the Mac II?  Am I correct
in thinking that the serial driver is of no help here?  Finally,
I can't be the first one to want to do this, is there a book or FAQ or
something pointing the way?  Thanks for any help that you can offer!

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