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Appendix C Functional Description C-21
Power is supplied to the diskette drive from a separate connector pigtailed from the
power supply. The diskette drive operates from the 5-Vdc supply and draws a
maximum power of 1.1 watts operating and 44 milliwatts in standby mode. The
diskette drive is connected to the SCSI backplane with a 34-pin ribbon cable.
Maximum cable length is 1.5 meters. From the SCSI backplane, it is cabled to the
motherboard with the SCSI connections.
C.1.10.3 Parallel Port
The parallel port is supported by an IEEE 1284-compatible parallel port controller
that is located on the SuperIO component. The parallel port controller is a
PC-industry-standard controller that achieves a 2-megabits per second (Mbps) data
transfer rate. The parallel port controller interface supports the ECP protocol as well
as the following:
■ Centronics – Provides a widely accepted parallel port interface.
■ Compatibility – Provides an asynchronous, byte-wide forward (host to
peripheral) channel with data and status lines used according to their original
definitions.
■ Nibble mode – Provides an asynchronous, reverse (peripheral-to-host) channel,
under control of the host. Data bytes are transmitted as two sequential, four-bit
nibbles using four peripheral-to-host status lines.
Parallel Port Cables
The parallel port cable is IEEE1284 compliant and consists of 18 pairs of signal wires
that are double shielded with braid and foil. The maximum length of the parallel
port cable is 2 meters.
Electrical Characteristics
Drivers operate at a nominal 5-Vdc transistor-transistor logic (TTL) levels. The
maximum open circuit voltage is 5.5 Vdc and the minimum is -0.5 Vdc. A logic
high-level signal is at least 2.4 Vdc at a source current of 0.32 mA and a logic
low-level signal is no more than 0.4 Vdc at a sink current of 14 mA.
Receivers also operate at nominal 5-Vdc TTL levels and can withstand peak voltage
transients between -2 Vdc and 7 Vdc without damage or improper operation. The
high-level threshold is less than or equal to 2.0 Vdc and the low-level threshold is at
least 0.8 Vdc. Sink current is less than or equal to 0.32 mA at 2.0 Vdc and source
current is less than or equal to 12 mA at 0.8 Vdc.