Re: swiftlink, disk image transfer

From: Marko Mäkelä (
Date: 2001-09-06 08:12:11

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

   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.


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