UPGRADING REPAIRING PCs

Port Type IRQ Usage DMA Usage Designed For Notes
ECP Yes DMA 3 High-speed Many systems offer
(Table 7.2) (Standard) printers, an EPP/ECP port
DMA 1 scanners setting for best
(Optional; results with all types
default on of parallel port
some Packard-
Bell models)
devices
Some older parallel printers don’t recommend either mode and
might print erratically if EPP or ECP modes are enabled. and ECP
ports
Prerequisites for EPP and ECP Modes
To use these advanced modes, you must
• Enable the appropriate mode on the parallel port (see previous
section)
• Use a parallel cable rated for IEEE-1284 uses
Parallel Port Connectors 191
The IEEE-1284–compatible printer cable transports all signal lines
to the printer, is heavily shielded, and produces very reliable printing
with old and new printers alike in any parallel port mode. IEEE-
1284 cables can also be purchased in a straight-through version for
use with printer-sharing devices.
Parallel Port Configurations
Table 7.2 lists the standard parallel port settings. While add-on
multi-I/O or parallel port cards can offer additional settings, other
settings will work only if software can be configured to use them.
Table 7.2 Parallel Interface I/O Port Addresses and Interrupts
Standard LPTx Alternate LPTx I/O Ports IRQ
LPT1 — 3BC-3BFh IRQ 7
LPT1 LPT2 378-37Ah IRQ 7 (LPT1)
IRQ 5 (LPT2)
LPT2 LPT3 278h-27Ah IRQ 5
Testing Parallel Ports
The most reliable way to test printer ports is to use a parallel port
testing program along with the appropriate loopback plug. This
method isolates the port and allows the system to capture output
back as input. Parallel port testing programs are included in major
diagnostic programs, such as Norton Utilities, CheckIt, AMIDiag,
QA+ family, MicroScope 2000, and many others.