IBM 3270 compatible terminal connected to Hercules IBM mainframe emulator.

Mattis Lind mattislind at
Sun Aug 30 01:23:41 CDT 2020

I have been working on a project for some time to connect a IBM3270
compatible Alfaskop terminal with its IBM 3274 compatible cluster
controller to the Hercules mainframe emulator.

Yesterday I eventually succeeded. I was able to login to TSO on my Hercules
system that ran MVS 3.8j.

Here are a couple quick video clips:

To achieve this I created a small piece of hardware I called SyncDongle,
essentially it's just a few level converters, connectors and a STM32F103
blue pill.

On the hardware I run a small piece of firmware, BSCBridge. It bridges
between the sync serial BSC used by the Alfaskop cluster controller and the
BSC variant that the 2703 emulation inside Hercules is using.

More information here:
and here

There are good chances that the SyncDongle/BSCBridge combo could work with
a 3274 or 3174 controller as well but I haven't tested since I don't have
one. But no guarantees given, though. If someone has a spare 3174-51R,
-61R, -81R or -91R I would be very interested in it.

Actually there is a good chance that it could work with general BSC use.
Maybe for NJE between Hercules and a real IBM machine? Or 2780/3780 RJE
terminals? Or other third party 3270 terminals using BSC.

The BSCBridge firmware only supports non transparent mode at this point, it
works fine with Alfaskop since it does not support anything else. Maybe a
showstopper for 3174 with 3279 terminals? SHouldn't be that difficult to
add transparent mode if needed.


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