"Interfacing the IBM PC parallel printer port" - читать интересную книгу автора (Stewart Z.)

One last electrical note: if you use any sort of bidirectional parallel port
for inputs, be sure to tristate it whenever it is connected to external
devices which will drive it. When I'm running it this way, I put a small
routine in my autoexec.bat which tristates the port in question on every
bootup. Or use inline resistors to at least limit the current to a safe
value.

Steven M. Scharf notes that some higher end parallel
port chips "lock" the direction control bit C5 to keep certain naive software
from accidentally changing the port direction. In particular, he says that
"PTR bit 7" of the National Semiconductor SuperI/O chip must be 1 before you
can change the direction control bit. I don't have documentation on this
chip, so I'm not sure what register PTR is; for now, consider this just a
warning. He says that other chips may lock the direction control
differently.

12. Enhanced Ports

There are at least two specs for further enhanced parallel ports, the EPP
(Enhanced Parallel Port) and the ECP (Enhanced Capability Port), with the
latter being more ambitious. I would appreciate any specs that can be
forwarded to me (or references) on either of these.


Steven M. Scharf gave this table:

Different Parallel Ports on NSC Parts
--------------------------------------------------------
PC87311 Bidirectional Parallel Port (16450 UARTS)
PC87312 Bidirectional Parallel Port (16550 UARTS)
PC87322 Enhanced Parallel Port (EPP) (16550 UARTS)*
PC87332 Enhanced Capabilities Port (ECP) also EPP 1.7 and 1.9 (16550 UARTS)*

*Floppy controller signals can be redirected out the parallel port pins
via an internal multiplexor. This feature is used in some sub-notebooks
with external floppy drives

13. Copy Protection Dongles

(From info provided by Steven M. Scharf )

Copy protection dongles typically watch the data lines for patterns of
data without any -strobe signal (pin 1, controlled by C0-). That is, the
copy protection software writes various patterns to the data lines without
every pulsing the -strobe line. Without a pulse on -strobe, any printer
also attached to the port should ignore this data. Not all dongles work
on all ports; this strobeless method is a bit more temperamental than
regular printer output.

Steven M. Scharf: "I heard one dongle manufacturer complain to me about

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