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Re: Apple IIGS Serial Input

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? 

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