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IEEE1284 Explained

The IEEE 1284 standard, called "Signalling Method for a Bi-directional Parallel peripheral Interface for Personal Computers", is used for bi-directional parallel printer bus support. It defines two interface levels; a physical and electrical interface.

The level 1 interface is for devices that need a reverse mode capabilities but do not operate at high speeds. The level II interface is for both bi-directional and high speed communications.

The 1284 standard also defines connectors for use in the parallel interface. The 25 pin DB25 connector is defined as the type "A" connector. The Telco 36, a 36 conductor, 0.085" centerline Champ connector with bale locks, is defined as the type "B"connector. The Type "C" connector is a 36 contact, 0.05" centerline mini connector with clip latches.

Additionally, the IEEE 1284 standard specifies;

  • All signals are twisted pair with a signal line twisted to its ground return
  • Each signal and ground return must have a characteristic impedance of 62 ±6 ohms over the frequency band of 4 to 16 MHz
  • The wire to wire crosstalk shall be no greater than 10%
  • The cable will have shielding with a minimum of 85% optical braid coverage over foil
  • The cable shield shall attach to the connector back shell using a 360° concentric method. A pigtail connection is not acceptable
  • Complaint cable assemblies shall be marked: "IEEE std. 1284-1994 Compliant".

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