Re: //c serial cable

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

<daimyo@powersurfr.com> wrote:

> I'm having no end of difficulty making my own //c serial cable.  I've
> received several conflicting accounts of the DIN 5 and DB9 pinouts.
> The one i'm using is:
> 
> 9 pins(WHILE LOOKING AT THE PIN SIDE! NOT THE SIDE THAT YOU INSERT THE
> WIRES IN!)
> 
> 1 2 3 4 5
>  6 7 8 9

If this is supposed to be the official pin numbers of a D-9 connector,
looking into the female plug, then it is backwards (they should be 5 4 3
2 1 on the top line, 9 8 7 6 on the bottom).  Note that the pins are
numbered on all D female and male plugs and sockets, so it is not
necessary to show the layout.

Functionally, the PC pins are:

1 DCD
2 RxD (data in)
3 TxD (data out)
4 DTR
5 Ground
6 DSR
7 RTS
8 CTS
9 RI (ring indicator)

> 5 pins(The same! While looking at the side that goes in the apple not
> the side that the wires come out of!)
> 1   5
>  2  4
>   3

This is the correct numbering for the IIc serial plug.

> Connect the wires like this
> 9pin                  5pin
> 1                     3       
> Nothing               1   
> 4                     2   
> 3                     4   
> 9                     5

No way is this correct.  Pin 1 on the PC is the DCD signal and pin 3 on
the IIc is ground.  It looks like the PC pins have been numbered
backwards.

Try this combination:

D-9        DIN-5
 ?          1         (Flow control from IIc)
 2          2         (Data from IIc)
 5          3         (Ground)
 3          4         (Data to IIc)
 4          5         (Flow control to IIc)

Pin 1 from the IIc probably doesn't need to go anywhere.  You might like
to connect it to any of pins 1 (DCD), 6 (DSR) or 8 (CTS) on the PC,
depending on what the software on the PC requires.  You could leave it
unconnected.

Pin 5 from the IIc can go to either pin 4 (DTR) or pin 7 (RTS) on the
PC, depending on what the software wants to do.  It must be connected to
an active flow control signal on the PC, or the IIc won't receive
anything.

As far as the IIc is concerned, the flow control signals are nominally
DTR (pin 1) and DSR (pin 5), but they are actually connected to the RTS
and DCD pins on the 6551 serial chip.  This means that deactivating the
output flow control signal (RTS) will prevent the IIc transmitting, and
deactivating the input flow control signal (DCD) will prevent the IIc
receiving.

> I've searched the web for this information and the DIN5 wiring pinout
> is not included in RS232C information

Not surprising, since the DIN-5 connector is nonstandard for RS-232
connections.  This connector and pinout is unique to the serial ports of
the Apple IIc.  It is documented in the IIc technical reference manual.

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