How I convinced my 1987 Canon Cat to talk to my 2017 MacBook Pro

2 min readNov 21, 2017

Canon Cat is a wonderful machine that means a lot me. I recently managed to get it to talk to my modern MacBook Pro. It took some time to figure it out, so I thought I’d share. It might also be useful info for connecting other older computers to newer ones via a serial port.

My Cat has a broken floppy drive — which is a common affliction — and my first attempts to connect it using a USB modem and phone cable failed. Here’s how to do the right way:

Ingredients

MacBook Pro running Mac OS 10.13.1 High Sierra.
One (1) Canon Cat.
A USB to serial converter. I bought Cable Matters USB to RS-232 DB9 Male Serial Cable. I understood this one was good since it was based on a Prolific PL 2303 chipset; there might be other options.
A female DB9 to male DB25 adapter.

Setup on a Mac

A (paid) driver from mac-usb-serial.com. The original (free) drivers for some reason didn’t work for me. Note that you have to enable a third-party KEXT using the Security & Privacy panel. (It should be relatively obvious what to do during installation.)

Setup on the Cat

Press [Use Front]+[Setup] a few times to go to Serial Port Connection.
Make sure it says Connect to: SEND Command (and not alternate printer).
Switch Communications mode to Full Duplex.
Switch Line terminator to CR/LF.
Leave other options as 9600/8 bits/no parity/1 stop bit.

Starting a conversation

Connect the USB to my computer, and the other side to the Cat through the adapter.
Power up both machines.
On the Mac, open Terminal and type cat /dev/tty.Repleo-PL2303-00006114. Note that the last digits might be different, usually you can just type all the way to Repleo and press [Tab] to autocomplete.
Press [Ctrl]+[C] to abort. I am not sure why these last two steps are necessary, but without them the communication only works one way.
Type screen -L /dev/tty.Repleo-PL2303-00006114.

You’re done!!!

What you type on your MacBook will appear on Cat’s screen immediately. To send more stuff, just copy and paste into the Terminal window.
You can select text using leaping, and press [Use Front]+[Send] to send it back to the Mac.
The -L option makes sure that the output is saved in a screenlog.0 file.

This experiment was made as part of writing a book about keyboards.