Standard 1983 MIDI 5-Pin DIN Pinout

This article details the standard pinout configuration of the 180-degree five-pin DIN connector defined in the original 1983 Musical Instrument Digital Interface (MIDI 1.0) specification. It breaks down the functional assignments of each pin, explains the electrical architecture of the 5 mA current loop system, and highlights the hardware differences between MIDI In, MIDI Out, and MIDI Thru ports.

The Connector and Physical Arrangement

The original 1983 MIDI specification utilizes a standard 180-degree 5-pin DIN connector (DIN 41524). Viewed from the mating face of a standard female panel-mount socket, the pins are arranged in a semicircle numbered sequentially in a non-linear DIN convention:

  • Pin 1: 45 degrees (lower left)
  • Pin 4: 90 degrees (upper left)
  • Pin 2: 135 degrees (top center)
  • Pin 5: 180 degrees (upper right)
  • Pin 3: 225 degrees (lower right)

Pinout Configuration

The 1983 MIDI standard deliberately utilizes only three of the five available pins for signal transmission, leaving two pins unconnected to prevent cross-compatibility issues with other audio DIN standards.

  • Pin 1 — Not Connected: Unassigned and left floating.
  • Pin 2 — Shield / Ground: Connected to the cable shield. In a MIDI Out or MIDI Thru port, Pin 2 is connected directly to the transmitting device's chassis/circuit ground. In a MIDI In port, Pin 2 is left unconnected to eliminate ground loops between networked equipment.
  • Pin 3 — Not Connected: Unassigned and left floating.
  • Pin 4 — Current Source (+5V / Data +): Supplies positive reference voltage. On MIDI Out, it is connected to a +5V rail through a 220-ohm current-limiting resistor. On MIDI In, it connects directly to the anode of the receiver's optocoupler LED.
  • Pin 5 — Current Sink (Data / Data -): Carries the inverted digital data stream. On MIDI Out, it connects through a 220-ohm resistor to the output of an open-collector inverter/buffer. On MIDI In, it connects directly to the cathode of the receiver's optocoupler LED.

Electrical Characteristics and Operation

The 1983 MIDI standard operates as a unidirectional, 5 mA current loop interface running at an asynchronous baud rate of 31.25 kbaud (±1%).

  • Logic "0" (Space / Active State): The transmitter pulls Pin 5 low, completing the electrical circuit from Pin 4 (+5V) through the external cable and into the receiver. Current flows through the optocoupler's LED on the MIDI In side, lighting the LED and pulling the receiving system's logic line low.
  • Logic "1" (Mark / Idle State): The transmitter leaves Pin 5 high (open/floating), preventing current from flowing. The optocoupler LED turns off, and a pull-up resistor on the receiver pulls the system's logic line high.

Optoisolation Design

A critical requirement of the 1983 specification is galvanic isolation at every MIDI In port using an optoisolator (such as the Sharp PC900 or HP 6N138). Because MIDI In relies entirely on the closed current loop across Pin 4 and Pin 5, no electrical connection exists between the grounds of the transmitter and receiver. This electrical decoupling prevents hum, audio interference, and destructive ground potential differences across connected musical hardware.