mat6013@DMZRZU71.BITNET (09/28/87)
I have not yet purchased the Apple IIgs hardware manual but want to connect an
acoustic coupler or modem with RS-232C interface to the internal modem port of
Apple IIgs as soon as possible. I'm not sure about the right wiring and the
meaning and difference of TxD+/TxD- and RxD+/RxD- on the 8-pin mini-DIN
outlet. So,
- how would a minimal connection (ground, TxD, RxD) look like,
- how a full featured (DSR, DTR, DCD);
- what's an appropriate configuration for the port to select in the control
panel (especially for handshaking) ?
Please respond directly thru email - immediate help would be greatly
appreciated.
Matthias Kapffer
<MAT6013@DMZRZU71.BITNET>NEY7@HBUNOS.BITNET (09/29/87)
For Matthias Kapffer's questions:
The wiring for a GS-serial-port and a modem,is as follows:
GS serial port Modem
1....>>...........DTR..............20
2.................DSR......<<.......6
3....>>...........TxD...............2
4.................GND...............7
5.................RxD......<<.......3
7.................DCD......<<.......8
1.The arrows mark the direction of the signal (i.e,DTR is output from the
modem into the computer etc,).
2.The numbers for on the GS port column assume the following numbering on the
connector:
+++# #+++
+ #__# +
+ 8 7 6 +
+ +
+ 5 4 3 +
+ +
+ 2 1 +
### ###
+# #+
++++
3.The numbers on the modem column assume the standart DB-25 RS232 connector.
As to 'minimal connection',I don't think there are many modems that would
compromise on DTR.Anyhow,lack of DSR and DCD is usualy more tolerable.
TxD+/TxD- and RxD+/RxD- is part of the glorious RS 422 concept,and more
accurately,of a method called 'differencial signal'.In this method,for each
of the Receive and Transmit signals,one wire carries the signal just as it
would on RS 232,and a second wire carries the first's inverse polarity.(Thus
the couples xD+/xD-).Now,the receiving device compares the xD+ to it's
inversed partner.If xD+ is higher than xD-,the receiving device reads 'high',
if it's lower,the device reads 'low'.What you get is a speed considerably
higher than on RS 232,and a connection much more emmune to noises.
You'll have to work out the appropriate Control-Panel configuration according
to the modem and software you use.
Yoram Ney
Hebrew University,Jerusalem
Bitnet:NEY7@HBUNOS