From: Groepaz (groepaz_at_gmx.net)
Date: 2003-10-20 19:15:14
On Monday 20 October 2003 11:44, Baltissen, GJPAA (Ruud) wrote:
> Hallo Groepaz,
>
> > almost every (SPP-) parallelport "behaves like" a 8255.
>
> This point of view is new for me. What computer(s) used a 8255 for their
> LPT-port?
> IBM did not. And most clones based their designs on the ones of IBM.
honestly, i neither know nor do i care. (although i believe there's an
8255 on the lpt card of my xt)
what i know is that all pc-docs i have (admittedly not much) refer to it,
and that programming it like these docs say always worked for me - across
all and every pc i tried so far.
what chip do you think ARE they using then btw? :) i cant even find a
reference to anything but 8255 in my docs (which are from 286' times, so
EPP isnt in them) [i've tried finding a reference on the net too, and
cant find *any* parallelport docs that mention the chips used at all :=P]
from help-pc:
:ports:port addresses:hardware ports
^PORTS Common I/O Port Addresses
[...]
% 060-067 8255 Programmable Peripheral Interface (PC,XT, PCjr)
060 8255 Port A keyboard input/output buffer (output PCjr)
061 8255 Port B output
062 8255 Port C input
063 8255 Command/Mode control register
[...]
% 380-38F Secondary Binary Synchronous Data Link Control (SDLC) adapter
380 On board 8255 port A, internal/external sense
381 On board 8255 port B, external modem interface
382 On board 8255 port C, internal control and gating
383 On board 8255 mode register
[...]
% 3A0-3AF Primary Binary Synchronous Data Link Control (SDLC) adapter
3A0 On board 8255 port A, internal/external sense
3A1 On board 8255 port B, external modem interface
3A2 On board 8255 port C, internal control and gating
3A3 On board 8255 mode register
[...]
:parallel port:printer port
^Parallel Printer Port
% Port 3BC printer data output (readable)
³7³6³5³4³3³2³1³0³ ports 278, 378, 3BC
³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ data bit 0, hardware pin 2
³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ data bit 1, hardware pin 3
³ ³ ³ ³ ³ ÀÄÄÄÄÄÄ data bit 2, hardware pin 4
³ ³ ³ ³ ÀÄÄÄÄÄÄÄ data bit 3, hardware pin 5
³ ³ ³ ÀÄÄÄÄÄÄÄÄ data bit 4, hardware pin 6
³ ³ ÀÄÄÄÄÄÄÄÄÄ data bit 5, hardware pin 7
³ ÀÄÄÄÄÄÄÄÄÄÄ data bit 6, hardware pin 8
ÀÄÄÄÄÄÄÄÄÄÄÄ data bit 7, hardware pin 9
% Port 3BD printer status register (Parallel Printer Port)
³7³6³5³4³3³2³1³0³ ports 279, 379, 3BD
³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = time-out
³ ³ ³ ³ ³ ÀÄÁÄÄÄÄÄ unused
³ ³ ³ ³ ÀÄÄÄÄÄÄÄÄ 1 = error, pin 15
³ ³ ³ ÀÄÄÄÄÄÄÄÄÄ 1 = on-line, pin 13
³ ³ ÀÄÄÄÄÄÄÄÄÄÄ 1 = out of paper, pin 12
³ ÀÄÄÄÄÄÄÄÄÄÄÄ 0 = Acknowledge, pin 10
ÀÄÄÄÄÄÄÄÄÄÄÄÄ 0 = busy, pin 11
% Port 3BE printer control register (Parallel Printer Port)
³7³6³5³4³3³2³1³0³ ports 27A, 37A, 3BE
³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = output data to printer, (pin 1)
³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 1 = auto line feed, (pin 14)
³ ³ ³ ³ ³ ÀÄÄÄÄÄÄ 0 = initialize printer, (pin 16)
³ ³ ³ ³ ÀÄÄÄÄÄÄÄ 1 = printer reads output, (pin 17)
³ ³ ³ ÀÄÄÄÄÄÄÄÄ 0 = IRQ disable,1=IRQ enable for ACK
ÀÄÁÄÁÄÄÄÄÄÄÄÄÄ unused
(please notice "data", "status", "control" refer to the *printer* here, not
to the i/o chip)
quite a bunch of 8255's in there, not only for printer port eh? :=)
> Using a 8255 has an advantage: it saves space, certainly in a
> laptop/dragable.
maybe in ancient designs :=P i pretty much doubt there are 8255's on any modern
boards - however even modern lpt ports (in SPP mode!) can be programmed as if
it was one.
> The disadvantage: it cannot be used as a bi-directional
> port using 'normal' software like Star Commander.
sure can - guess what the "SPP" setting is good for. (also, 4bit bi-directional
transfer isnt a problem at all - check the original PC-64 cable, or one of these
custom crossassembler cables)
> The used 8255-port is
> bi-directional but changing its direction means writing to the command
> register, one the IBM bi-directional LPT-port doesn't know.
guess why i wrote SPP port - they arent "bi-directional" like EPP is.
gpz
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