Re: //c adventures...

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

Dave Althoff <dalloff@freenet.columbus.oh.us> wrote:

> Well, I just successfully connected my Psion 3a and my //c and got them
> talking to each other at 19,200 baud.  A couple of things I encountered--
> 
> 1)  For the pinouts, I consulted Nathan's FAQ.  I should note that based
> on the DIN-5 connector I have, he has the pin numbers misidentified.  But
> he does have the correct signal associated with the correct position on
> the connector, so ignore any numbers that happen to appear on the
> connector frame.

I haven't checked the FAQ, but Nathan probably has a copy of one of my
messages (or equivalent) which documents the DIN-5 pin numbers of the
IIc serial ports as:

5       1
 4     2
    3

This is not the standard numbering of the DIN-5, but it is how it is
labelled in the Apple IIc Technical Reference.

> I am aware that some //c's have trouble communicating at certain speeds
> through the modem port.

It isn't specific to the modem port, just to the type of device
connected to either port.  The same clock source drives both ports with
a slightly out of spec clock speed.  The end result is that the IIc
transmit baud rates are about 3% slower than the quoted values.  If the
receiving device isn't too fussy, this doesn't cause problems.  Printers
and dumb modems (300 bps) generally fall into this category.

Smart modems, on the other hand, are much fussier about character
timing, e.g. using it to auto-detect the baud rate of the host.  Some
modems are fussier than others.

There may also be problems in the receive direction, because the IIc
sees the standard baud rate as being slightly too fast.  This may cause
character corruption in continuous receive data.

Officially, the problem prevents any 1200 bps or faster modem from
working properly with the original IIc motherboard.  Unofficially, it
doesn't always cause problems - it depends on the device.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand