Using Kermit to Serial Transfer Files

I recently restored my Compaq Portable II. If you haven’t read Open (Link) about the forming of Compaq I would suggest it, I highly enjoyed it. In doing so I thought I would transfer some files to the 286 via serial, instead of taking the Compact Flash card it ran on out of the adapter, and then copying new software.

I started my journey thinking I would use the old Microsoft Interlnk software that came with MS-DOS 6.22, and then perhaps a virtual machine on laptop to serve the files. The laptop I had on hand was a Macbook Pro, I thought I could do a MS-DOS vm, then hook the USB serial adapter up to the vm allowing MS-DOS to see it as COM1. This turned into a giant headache, VMware and Virtualbox (I tried both) kept giving me errors. They really didn’t like the USB serial adapter (who does), after a few hours of playing with it I made a silly decision of: the easier way would be write a new InterLnk server in Java and let my modern OS talk to DOS directly.

I spent some time configure two Vmware Fusion vms’ to have virtual serial lines go to named pipes. Then I had socat interconnect the two pipes and log the traffic, (I put the command below if anyone is interested). On one hand, I found it interesting researching debugging serial communications using virtual machines. On the other hand, after more time than I care to admit, I didn’t see a clear pattern to the serial data, along with was getting the data going between the systems but not in a super clear format, Wireshark has spoiled me. I finally decided it was time to try another plan. A quick detour to try to decompile the app made me more confused than ever, and we were back searching for a new method of connection.

socat -v -x GOPEN:/Users/Dan/DOS/pipe GOPEN:/Users/Dan/DOS/pipe2

After researching different methods of serial file transfer, such as xmodem, ymodem, and Kermit; I thought I would give Kermit a try. I have used xmodem for dead Cisco devices, and thought Kermit would be easiest to server from my Mac. It allows things like packets in the protocol, which makes it be able to speed up and slow down transfers as the transfer goes on.

To configure the server on the laptop I used Homebrew, installing with:

brew install c-kermit

Then I loaded the app via the Compact Flash card for the Portable. I got Kermit for DOS off of . Version 4 for DOS works mostly the same as version 9 from Homebrew. The app lets you change directory to a folder you want to operate out of, set your connection settings, which I have below. Then you hit the command “receive” or just “r” on one side to receive. The other side then pushes whichever file you want.


set port com1           # Or COM2 or whatever the port is

set carrier-watch off   # Assume there is no carrier signal

set speed 57600         # Or whatever the speed has to be



set port /dev/tty.usbserial

set carrier-watch off   # Assume there is no carrier signal

set speed 57600          # Or whatever the speed has to be


I selected 57600 because I was not sure if the Compaq could handle the next jump to 115200. This page has a lot of info about setting up the program, there are a lot of dials and knobs that can be moved.

You can bring up a serial connection between the two and just type messages, but in the end I remembered how slow serial links were. I ended up powering off the system, pulling the Compact Flash card and then loading most files that way. Sort of felt like cheating, but when transferring the Windows 3.0 install files were going to be a 15 minute plus affair, I want to the good ol’ USB 3.0 Compact Flash Reader.


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