Re: Apple IIGS Serial Input

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

Smohn Jith <Smohn@smohn.com> wrote:

> On 4/4/2013 7:00 PM, David Empson wrote:
> > Smohn Jith <Smohn@smohn.com> wrote:
> >
> >> I have a device that has 3 wire RS232 serial.  TxD, RXD, and Ground.
> >> I'm trying to get it to work with my IIGS.  I succeeded in this 10 or
> >> more years ago and I forgot what I did.  I have the 3 wires hooked up
> >> correctly, but I vaguely remember having to ground the handshake pins or
> >> the General purpose input pin or something.  I've tried a bunch of
> >> combinations without luck.  Any ideas?
> >
> > The IIgs serial port uses RS-422 for its transmit and receive lines.
> > RS-422 has a balanced pair of signals: TxD+ and TxD-, and RxD+ and RxD-.
> >
> > If you are hooking up an RS-232 device, you use the TxD- and RxD- pair
> > on the IIgs. You can ignore TxD+, but you must connect RxD+ to ground,
> > otherwise the receive signal doesn't work properly (it is comparing the
> > voltages on RxD+ and RxD-, so uses the ground on RxD- as a reference).
> >
> > <http://apple2.info/wiki/index.php?title=Pinouts#Mini_DIN-8_Serial_Port_
> > .28GS.2C_IIc_Plus.2C_Macintosh.29>
> >
> I've done that and still no dice.  Is there a pin a need to ground or
> power to make the RTS/CTS work, or actually not work as there will be no
> handshaking?

That would typically be a software setting, telling it disable
handshaking. Unlike the 6551 (used on the Super Serial Card and in the
Apple IIc), the Z8530 (used in the IIgs) can be told to ignore the flow
control signals.

Handshake Out (pin 1) can be ignored if there is nowhere to connect it
on the other device.

Handshake In (pin 2) might need to be active if the software can't
ignore flow control. A possibility here would be to loop pin 1 to pin 2.

The General Purpose Input (pin 7) is often used for DCD with a dial-up
modem, used to detect loss of connection, but otherwise isn't important.

Are you sure you have the signals the right way round? The names of the
signals on pins 1-8 (as shown in the diagram from my link above) refer
to the signals from the point of view of the IIgs. The details of the
pinout at the printer end in the diagram refer to the signals from the
printer's point of view, e.g. the printer receives data on pin 3.

If you were connecting to a modem, the logic is reversed for the names
of the transmit/receive pins: a modem's "TxD" pin refers to the pin on
which the modem receives data from the computer/terminal to transmit to
the telephone line.

> I'm using Proterm 3.0 with a Null Modem driver.

I've never used Proterm but I expect it can be set to ignore flow
control.

-- 
David Empson
dempson@actrix.gen.nz