Re: Data Conversion Question - Apple II ---> Centris 650

[valthoff@magnus.acs.ohio-state.edu (Victoria M Althoff)]

A null modem cable is just a serial cable connected between the serial ports on
two computers.  Each serial port has several important lines.  These are 
defined by the RS-232 standard as follows for a DB-25 connector, such as you 
find on an Apple ][ Super Serial Card:

Pin   Signal
1     Protective Ground
2     Transmitted Data
3     Received Data
7     Signal Ground
In addition, there are less-critical handshaking lines:
4     Request to Send
5     Clear to Send

The terminal jumper on the SSC swaps the positions of certain lines, notably 
the transmit and receive lines.  All a null modem cable does is connect the 
transmit data of one computer to the receive data of the other, and vice-versa.
 The ground (signal) is wired straight through, and the handshaking lines can 
usually be tied together (i.e. jumper pins 4 and 5 on the SSC) since they are 
not used by most data protocols.

In terms of software, you need a basic terminal program running on both 
machines.  Ideally, both should offer a good high-speed data transfer protocol,
say, ZMODEM.  Set the baud rates of both machines as high as you dare (9600 
baud should do it), and use the terminal program to transfer the data.  If 
you're using a smart program like ProTERM, you may have to work with it a bit 
to get it to force terminal mode without a modem.  Other than that, it's really
quite simple.  If you have a ][e equipped with an Imagewriter II, just connect 
the printer end of your printer cable to the serial port on your Macintosh.  
Then try running your terminal program.  If you can't type between the 
computers, power down and reverse the jumper block on the ][e's SSC, changing 
the setting from 'PRINTER' to "MODEM".  As noted, that will swap the data lines
for you.  Obviously, you should tell your ][e terminal program to use the 
printer slot as your modem.

Good luck!
--Dave Althoff, Jr.