Keyboard inverters/converters for terminals

Eric Smith spacewar at
Thu May 21 12:20:17 CDT 2020

On Thu, May 21, 2020 at 9:37 AM Electronics Plus via cctalk <
cctalk at> wrote:

> Type in keyboard
> The first result allows a terminal keyboard to be used on a PS/2 port.
> The second result allows a PS/2 keyboard to be used on a terminal.

>From the limited information available (almost none), it appears that they
are selling passive adapters that work with ADDS 4000 terminals that use
PS/2 protocol on a modular jack.

As has been noted earlier in this thread, there are a huge number of
computers that use modular plugs and jacks for keyboard interfaces, and
there is NO standard for their electrical or protocol characteristics.
Plugging in the wrong combination can result in damage to either or both
devices. Even using the wrong modular cable can do that, because common
4P4C modular cables are wired with a flip (1 to 4, 2 to 3, etc), while
modular cables for computers are sometimes (e.g. Macintosh 128/512/Plus)
wired straight through (1 to 1, 2 to 2, etc.)

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.

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

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