Re: IIc+ (was HELP!)

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

In article <C080295112224.5747@tap.fnet.org>,  <Cygnus@tap.fnet.org> wrote:
> Beautiful machine.

By the way, it would have helped if you said _which_ machine you had.
I managed to work it out by reading ahead, but the first paragraph
was a little confusing until then...

> But a few things are driving me nuts... First off, it switched from
> the din-5 serial connectors to the mini din-8s. So I figure GREAT! I
> can run reliably at 14.4, right?

What does that have to do with the type of connector?

The IIc+ serial ports are identical in design to those of the IIc,
apart from the connector.  They have the same serial chip (6551) and
flow control lines, so the IIc+ suffers from exactly the same problems
as the IIc regarding hardware handshaking (in short, it doesn't work).

The IIc+ serial signals are electrically the same as the IIc (+/-12V,
RS-232) not the IIgs or Mac (+/-5V, RS-422 or RS-423).  The "TxD+",
"GPI" and "RxD+" pins (6, 7 and 8) are not connected inside the IIc+.

The detailed description of the flow control problems with the
IIc/IIc+ when using hardware handshaking:

Outgoing flow control: this is supposed to be turned off if the
computer wants the modem to stop sending data to the computer.  In the
case of the IIc/IIc+ it also prevents the computer from sending to the
modem.  This just slows down data transfer, and isn't fatal.

Incoming flow control: this is supposed to be turned off if the modem
wants the computer to stop sending data to the modem.  In the case of
the IIc/IIc+ it also prevents the computer from RECEIVING any data
sent by the modem - anything the modem sends will disappear into the
ether.  The only way to minimise this problem is for the comms
software to turn off the outgoing flow control line as quickly as
possible, which will correctly stop data flow in both directions.

Every time this happens, the computer will lose some data, requiring a
retransmission if a file transfer is in progress (it could wipe out a
block acknowledgement when uploading, for example).

This will only be a real problem when a reasonably large amount of data
is being sent both ways at the same time.  Most of the time, data is
either being sent or being received.  Unfortunately, speed buffering in
the modem will tend to increase the proportion of time in which the
modem's outgoing flow control line is off.

To avoid potential problems, the IIc and IIc+ should be run at 9600
without error correction, data compression or hardware handshaking.

> Problem number 2: I'm looking to turn this thing into a notebook. Apple
> switched from the brick-on-a-rope power supply to an internal. Meaning the
> jack in the back requires 120v ac. Meaning I have to jury-rig a battery pack,
> battery pack connector, and power supply selector switch (for selecting
> between the battery and the ac). Does the //c+ have basically the same
> internal power supply wiring and power requirements as the older //c's?

The internal connector is completely different, as is the internal
power supply.  The IIc has a 44-pin connector with lots of ground
signals, a couple of -12V signals, five +12FIN, four +5V, three +12V
and something called "FFF" which goes to the switch on the back panel.

The IIc+ has a 7-pin connector with three grounds, two +5V, one +12V
and one -12V.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand