Re: IIGS Serial ports

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

Frank Carney <frankc@cyberhighway.net> wrote:

> So what you are saying is that the EIA422 is compatible enough to allow
> a EIA232 device to connect to it?

Provided the RS-422 device has been implemented with this capability in
mind.

In the case of the IIgs and Mac, the main rules for connecting an RS-232
device are:

1. The signal ground on the IIgs (pin 4) must go to the signal ground on
the RS-232 device (e.g. pin 7 on a DB-25, or pin 5 on a DE-9).

2. The TxD- output from the IIgs (pin 3) goes to the data input of the
RS-232 device.

3. The TxD+ output from the IIgs (pin 6) is not connected.

4. The RxD- input to the IIgs (pin 5) goes to the data output of the
RS-232 device.

5. The RxD+ input to the IIgs (pin 8) must be connected to signal
ground.  (This is required to correctly bias the RS-422 receiver to deal
with the positive/negative swing of the RS-232 transmitter.)

The flow control lines are single-ended, so they can be connected
directly to the appropriate pins on the RS-232 device.

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