IEEE 1284 Connectors
The 1284 standard goes beyond describing new data transfer modes
and actually defines the mechanical interface and the electrical
properties of a compliant parallel port. Many of the problems associated
with parallel port-attached devices arise from the fact that there
has been no standard for the electrical interface for the parallel
port. The DB25 female connector has become standard for the PC or
host connector, but there have been many different implementations
of the drivers, resistors, capacitors, etc, for electrical the interface.
The
1284 committee felt that it was paramount to define what these properties
should be in order to meet the following objectives:
- Ensure
electrical and mechanical compatibility among all 1284 compliant
devices.
- Ensure
that 1284 interfaces would operate with existing parallel port
peripherals and adapters.
- Ensure
operation and data integrity at the highest data rates
- Extend
operation to 10M (30')
To
meet these objectives, the standard defines the connectors, electrical
interface, and cable requirements.
1284
Connectors
The
standard identifies three types of connectors for a 1284 interface.
- 1284
Type A
- 25
pin DB25
- 1284
Type B
- 36
Conductor, .085 centerline Champ connector with bale locks
- 1284
Type C
- 36
conductor, .050 centerline mini connector with clip latches
Figure
1 shows what these connectors look like.
Figure
1 -- 1284 Interface I/O Connectors
The
type C connector is the one recommended for new designs. This connector
offers a smaller footprint than the previous connectors, has a simple-to-use
clip latch for cable retention, and provides for the easiest cable
assembly with the optimal electrical properties. In addition, a
cable assembly built with this connector provides for two more signals.
These signals are Peripheral Logic High and Host Logic High. These
signals may be used to determine if the device at the other end
of the cable is powered on. This enables some degree of intelligent
power management for 1284 interfaces.
