Re: Apple //c plus serial pinouts?

[dempson@actrix.gen.nz (David Empson)]

In article <CpLvyy.A6n@crash.cts.com>,
Randy Shackelford <shack@crash.cts.com> wrote:
> In article <CpL6nw.JqD@actrix.gen.nz>,
> David Empson <dempson@actrix.gen.nz> wrote:
> 
> >2. The IIc+ doesn't have the "general purpose input" on pin 7.  Nor
> >does the Mac Plus, but the IIgs and later Macs do have this pin.
> 
> Pluses, LC's, and Classics are all missing the GPI signal the way I
> hear.

Thanks for the update.  The only hardware info I have on Macs is
Inside Mac Volume 4, which covers the Plus.  Someone told me that it
was on the SE and all later Macs, but it seems there are exceptions.

Pin 7 is definitely unused on the Plus.  (Earlier Macs use a DB-9
serial port, with a totally different pinout including power supply
signals.)

> What does this signal even do?

It goes to the Carrier Detect input of the SCC chip.  It basically
gives you a second incoming flow control line.  The IIgs refers to it
as "DCD" in the control panel, and lets you enable "DCD Handshaking",
which has nothing to do with the normal function of the DCD signal
from a modem.  It appears to be intended to use this input as a CTS
signal (in fact, there is a standard DB-25 to Mini-Din-8 adaptor
available from Apple which has the RTS and CTS pins connected together
and going to the General Purpose Input on the IIgs).
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand