On Wed, 5 Sep 2001, Cameron Kaiser wrote:
> Macs never really were RS-232, though, but RS-422. I don't know if that
> makes much difference to your circuit design or not.
According to http://www.public.usit.net/marty104/pubs/Mac-ISDN-FAQ.html:
The ISDN modem connects to your Macintosh with an RS-232 to DIN 8
hardware handshaking cable. If you are using a 14.4 Kbps or faster
modem now, you likely already have one of these cables. The Mac
Connection sells them (part # 01093) for $14.95.
I think one can build the cable much cheaper than this. From the Linux
Serial HOWTO v2.08 (June 2000), chapter 18.2: [...] "The Mac used a small
round "mini-DIN-8" connector. It also provided conventional EIA-232 but
at only at 5 volts (which is still legal EIA-232). To make it work like
at EIA-232 one must use a special cable which (signal) grounds RxD+ (one
side of a balanced pair) and use RxD- as the receive pin. While TxD- is
used as the transmit pin, for some reason TxD+ should not be grounded."
By the way, last night I implemented a pulse width measurement mode in the
device. Since I used C-Kermit on Linux to drive it, I haven't analyzed
any data yet. It looked like there was a short pause in the pulse stream
between the tape header and the actual data when I executed a plain SAVE
command with no program in memory. I also noticed that an idle mode in
the device is definitely needed, since the cassette write signal is
connected to a keyboard line in the VIC-20.
Marko
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