better known as the IEEE 1284 standard. IEEE 1284 incorporates the two pre-existing par-
allel port standards that were already in use with a new protocol to create an all-encom-
passing parallel port model and protocol standard.
The IEEE 1284 standards are as follows: Standard Parallel Port (SPP) This standard defines a simplex parallel port
that allows data to travel in one direction only—from the computer to the
printer. This standard is included to support very old legacy printers.
Enhanced Parallel Port (EPP) This standard defines a half-duplex parallel
port that allows data to flow in two directions, but only in one direction at a
time. This allows the printer to communicate with the PC or a network adapter
to signal that it is out of paper, its cover is open, and so on.
Enhanced Capabilities Port (ECP) If a PC lists that it has an IEEE 1284–
compliant parallel port, it typically means that it has an ECP port. The ECP
standard allows bidirectional, simultaneous communications between the
printer or parallel device to the PC or network. The IEEE 1284 standard also
defines a special cable that is required by the ECP standard. The EPP standard
is technically bidirectional, but remember that it is only a half-duplex standard. So,
when shopping for a printer cable, be sure you get an ECP cable to work with
your ECP parallel port.Configuring and Troubleshooting a Parallel Port
In a majority of cases, problems with a parallel port are in the device attached to it. A par-
allelportisvirtuallyfeaturelessanditeitherworks(anditusuallydoes)oritdoesn’t.Any
problem that is specific to the parallel port is either in the connector or port (bent pins or
blocked holes), the cable (wrong type—SPP, EPP, or ECP), or the device itself.
There is always an outside chance that a system resource conflict may exist, but this
problem is caused by new devices being added to the PC. ECP devices, including some
printers, use IRQs and DMA channels (see Chapter 13). Most printers don’t use the sys-
tem resource allocations made to a parallel port. However, when a problem shows up
that you have isolated to the parallel port, check for system resource conflicts, especially
if a new piece of hardware has just been added to the PC.
The following table lists the default system resource assignments for parallel ports
used on most PCs:Port IRQ I/O Address DMA Channel
LPT1 IRQ 7 378h DMA 3 (ECP Capabilities)
LPT2 IRQ 5 278h n/a(^492) PC Hardware: A Beginner’s Guide