Keyboard inverters/converters for terminals

Rico Pajarola rp at
Thu May 21 20:42:03 CDT 2020

On Thu, May 21, 2020 at 10:20 AM Eric Smith via cctalk <
cctalk at> wrote:

> IMNSHO, there's a special place in hell reserved for those who have
> designed equipment to (ab)use modular connectors other than for telephone
> lines and 10BASEx Ethernet, and I really think a better connector should
> have been chosen for 10BASEx.
The whole concept of "if the plug fits, it will at least not blow up" is
kind of a late invention.

And I'm amazed when this actually holds true in situations where I wouldn't
quite expect that to be the case (e.g. all those electrically not quite
compatible PCI/PCI-X/PCIe variants that have coded notches to prevent you
from frying your computer/card. Except that you can stick a PCI card
backwards into a PCIe slot)

DEC using MMJ may get a pass because they at least attempted to prevent
> connecting the wrong stuff together.

Any ideas why it took so much longer for keyboard interfaces to converge
than most other peripherals? Display interfaces, HDDs/floppies/tapes etc.,
serial ports, and even mice converged on only a few variants more or less
the moment they became commonplace.

I'd really like some first hand insight into why anyone would want to
invent a new interface/protocol from scratch every time they
start developing a new machine (I'm mostly talking about the "simple async
serial protocol sending up/down events" kind). Luckily there are only 12
different ways to wire a 4P4C, but there exist way more incompatible
keyboards using that connector. Is it really easier to develop an
incompatible serial keyboard interface from scratch than to re-use one that
already exists?

[actually, I kinda know, because of course it's easier to do a one-off and
not care about documentation, licensing, extensibility, or
forwards/backwards compatibility]

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