imported>Kbrose: rm, Ethernet uses 8-pin connectors, not 6P6C

2025-03-19T03:39:20Z

rm, Ethernet uses 8-pin connectors, not 6P6C

New page

{{Short description|Serial port connector type}}
{{refimprove|date=October 2020}}
{{Infobox connector
|name=Modified Modular Jack
|type=[[RS-423]] serial
|image=RJ DEC Type.jpg
|logo=
|caption=MMJ socket and plug
|designer=[[Digital Equipment Corporation]]
|design_date=
|manufacturer=
|production_date=
|superseded=
|superseded_by=
|superseded_by_date=
|external=
|hotplug=
|length=
|width=
|height=
|electrical=
|ground=
|maximum_voltage=
|maximum_current=
|audio_signal=
|video_signal=
|data_signal=
|data_bit_width=
|data_bandwidth=
|data_devices=
|data_style=
|cable=
|physical_connector=
|num_pins=
|pinout_col1_name=
|pinout_col2_name=
|pinout_image=[[File:MMJ-socket pinout.svg|150px]]
|pinout_caption=
|pin1=DTR
|pin1_name=Data terminal ready
|pin2=Tx+
|pin2_name=Transmit data
|pin3=Tx-
|pin3_name=Transmit data ground
|pin4=Rx-
|pin4_name=Receive data ground
|pin5=Rx+
|pin5_name=Receive data
|pin6=DSR
|pin6_name=Data set ready
|pinout_notes=
}}
The '''Modified Modular Jack''' ('''MMJ''') is a small form-factor [[serial port]] connector developed by [[Digital Equipment Corporation]] (DEC). It uses a modified version of the 6P6C [[modular connector]] with the latch displaced off-center so that standard modular connectors for telephone jacks cannot accidentally be plugged in. MMJ connections are used on Digital [[minicomputer]]s, such as the [[PDP-11]], [[VAX]] and [[DEC Alpha|Alpha]] systems, and to connect terminals, printers, and serial [[console server]]s.<ref>Andrew Oliviero, Bill Woodward ''Cabling: The Complete Guide to Copper and Fiber-Optic Networking'',
John Wiley & Sons, 2009, {{isbn|978-1-118-80734-7}}, page 295 </ref>

The MMJ connector has six conductors. As defined by DEC, the six pins are Tx and Rx for the data transmission, their return paths, and DSR and DTR for handshaking. The transmit and receive signals are differential: each signal is the voltage difference between the line and its associated ground, as opposed to a voltage on a single connector relative to a common reference. The electrical signaling is defined by the EIA [[RS-422]] standard. The system can interoperate with RS-232 signaling by shorting the lower voltage sides of each signal to the RS-232 signal ground line. In this case, RS-232 limits apply to data rate and cable length.

When connecting two DTE devices such as a computer and a printer, the Digital BC16E [[crossover cable]] is used.

The DEC VT320 and TI/HP-928 were terminals offering an MMJ option. Using RS-422 signaling over 6-conductor RJ12, cables could be up to 1000 meters.<ref>{{cite web |title=HP:Terminal Cable Handbook|url=http://www.bitsavers.org/pdf/hp/terminal/5957-9918_terminalCableHbk.pdf|website=Bitsavers.org |access-date=2024-05-21}}</ref>{{fv|date=June 2024}}

Thrustmaster is using the MMJ connector for connecting its line of rudder pedals and racing pedals to either USB via a proprietary Thrustmaster Adapter, or directly to a joystick or racing wheel.{{cn|date=August 2019}}

The [[Lego Mindstorms]] NXT and EV3 set used connectors similar to MMJ for motors and sensors. This was to prevent the connection of standard telephone cords. The MMJ connector used by LEGO is also taller than those used with data terminals.<ref>{{cite web |title=Mindstorms EV3 Hardware Development Kit |url=https://education.lego.com/en-us/product-resources/mindstorms-ev3/downloads/developer-kits/ |website=lego.com |publisher=LEGO |access-date=2024-05-21}}</ref>

[[CEA-909]] uses the MMJ connector for control signals to a smart antenna, which can either physically or electrically rotate for maximum signal strength.

==See also==
* [[Serial console]]

==References==
<references/>

== External links ==
*[http://www.lammertbies.nl/comm/cable/dec-mmj.html Wiring schemes for Modified Modular Jack cables and converters]
*[https://tldp.org/HOWTO/Text-Terminal-HOWTO-12.html#rj_conn Linux Documentation Project: Connectors and Adapter Types]
[[Category:Networking hardware]]

Modified Modular Jack - Revision history

imported>Kbrose: rm, Ethernet uses 8-pin connectors, not 6P6C