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Talking to an autistic Macintosh Classic


Veteran Member
Apr 24, 2009
Canberra, Australia
In the VC Forum thread "AppleTalk from Mac Classic to Ethernet on iMac G3" I got a range of advice on how to get data off a Macintosh Classic with very limited software and hardware options.

The Classic had System 7.0 installed, which did not include PC Exchange for read-write of PC floppies. Nor did this installation have any AppleTalk link active.

The options for communication were:

1. 8-pin min-DIN serial port
2. DB25 SCSI port
3. Floppy "Superdrive" ("Super" here means it can read 1.4MB floppies as well as older Apple 400/800K floppies)

My first aim was to get a communications link into the Classic. We're all networked, right?

The Classic has only obsolete networking capabilities. Even modem communications require an external modem. That was the baseline.

I had an old K56Flex modem left over from dial-up days, so needed an adapter from the Classic's 8-pin miniDIN to the modems D25 serial port. These adapters can be bought online, but to save time I made my own. Pinouts are available online, at Apple's support site and other Apple forums.

When I make an adapter for an unusual plug or socket, I like to make it configurable. The mini-DIN is a nuisance to solder, but fortunately only five of the eight lines are needed (others are bridged at the plug). At the D25 end, I solder terminal pins onto the solder cups of the D25 male plug, then crimp matrix sockets onto the wires. This way, the configuration can be changed easily by replugging the wires for testing or different uses - eg for null modem if required.

Here are pictures of my adapter.

View attachment 5238 View attachment 5239

For straight modem communication from a Classic, I could use ClarisWorks by opening a new "communications" file. The modem setting has to be "Serial Tool", not AppleModem. Hardware handshaking will work on DTR/CTS setting. Since there will be no dialling, the modem setup initialisation string is ATX3&C0, which you enter in the window after opening the session. You initialise the modem at the other end with ATX3&C0 (it might work without the &C0, but no harm using it both ends. Either end then initiates the session with ATD, and the other responds with ATA. The modems then negotiate connection speed and handshaking.

I tried this with three different modems and machines at the other end.

A Compaq Armada 1700 with internal modem managed only 21kbps connection.

A P4 PC with USB modem managed 31kbps.

My iMac with internal modem managed 33kbps connection.

File transfers can only be done using basic XMODEM. The Classic with System 7.0/ClarisWorks can't do better than that.

Actual data throughput is accurate but very slow - 3.5kbps. That means more than an hour per floppy disk image.

After more reading I realised that I should be able to make direct serial-to-serial connections without modem. I had a USB-to-serial adapter (U232-P9) that I had used years ago on another old laptop. Driver for MacOSX was available online, so I installed it. ZTERM ($20 shareware) can handle it and ZTERM's website shows how to make sure ZTERM can find the port. Then it is a matter of changing ZTERM's "Modem Settings" off the built-in modem and selecting the new port from ZTERM's dropdown list choice.

ZTERM calls this direct connection "Local". No AT commands needed. File transfers with XMODEM can be selected with a couple of keystrokes.

For direct serial sessions from ClarisWorks, no changes are needed from the modem file except that the connection opens immediately without any AT commands. File transfer works exactly as before, but faster.

Direct serial between ClarisWorks and Zterm got throughput of 5.8kbps. That's almost double the speed using modem, but still about 30 minutes per megabyte.

IMPORTANT: There is no need to reconfigure the adapter for direct serial - it DOES NOT need null modem wiring.

So the serial port is a safe fallback and OK for short content file transfers, but a pain for large-scale transfers such as system upgrades. The Classic can take System 7.5.3, which comes as 20 floppy-image files (including the 7.5 "Network Access" file that you need to boot into the floppy images - 7.0 can't upgrade itself to 7.5.3!)

System 7.0 also has no PC Exchange or AppleExchange for floppy conversions, so I had to manage the floppy conversions on a PC.

I downloaded several freeware/shareware products to evaluate and would only recommend TransMac (Shareware with 15-day trial). With TransMac on a PC I could copy each floppy image in turn onto a Mac-formatted diskette, transfer it to the Classic, read it, eject it, and put it back in the PC drive for the next file.

The Classic did not like the same diskette re-appearing with different content. Several times it had to be re-started. The process also only worked consistently with diskettes formatted on the Classic. Diskettes formatted by TransMac on the PC were not so reliable. Probably there is a small difference in alignment, and/or alignment tolerance, between the floppy drives on the different machines - but maybe some other formatting issue.

Installing the System upgrade confirmed another reason to get a SCSI external drive. The Classic HDD is only 40Mb, which is not big enough to do a full system install of 7.5.3 without first wiping the whole HDD. I wanted to keep some applications which have no source disks anymore, so did not want to wipe the disk. That meant I could only make a minimal install of the upgraded system, omitting all kinds of items including AppleTalk.

With a SCSI external drive (ZIP or HDD), the 20Mb+ of install files can be kept off the internal HDD, so there will be room for a full system install.

Clearly a ZIP would be most useful, but only if you have a) a second, networkable machine with a SCSI port or b) a second ZIP drive with parallel or USB interface. I'm keeping my eye out for something within budget, but might be satisfied now with a SCSI HDD for backup and install.

It's not as though there are going to be further software upgrades for the Mac Classic, and there's no way I will be generating significant content on it. I just want it cleaned up, sitting politely on the shelf, and giving me that little Mac smile whenever I turn it on.